Spark plugs?

[B0000M]

i went to spectrum a couple of weeks ago, to grab a spark plug.

ive always run BR9EV's in my CR, and my bike occaisonally gets a bit of detonation.

i asked the guy there for a 9, he seemed surprised, and asked if i ever get detonation, i said yea sometimes, he said i should be running a 8.

i havnt done any riding since, but i thought id confirm my suspicions online and i was right in that a 8 range ngk plug is a hotter plug than a 9 range.


from what ive just read, it would appear that running a hotter plug is going to make my problem worse.

do we have any experts here?

scott411?
reckless?

[CookMySock]

Champion use lower numbers for colder plugs, while NGK and Denso use higher numbers for colder heat ranges. (<a href="http://www.carcraft.com/howto/116_0703_spark_plug_guide/heat_range.html">references</a>)

So you have to figure out whether the larger number will allow the plug to run at a higher temperature or lower temperature. But yeah, a hotter plug will be more prone to detonation for sure.. but which way is hotter or colder depends on the manufacturer.

Steve

[Reckless]

I've always associated detonation more to ignition timing rather than plug temp. Although I would have guessed the hotter it is in there the more likelyhood of detonation. Now if I remember rightly your Cr should run a BR8 as standard so if you say its detonating sometimes on a colder BR9 its worth getting the dail guage out and having a check on the timing I reckon.

Here's a bit of a read for you to save me typing it.

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.

you might find setting the timing to standard or a fraction of retard might be a good thing, make it smoother and give you a bit of over rev.
You might also find you can try the Br8 and its better. I could run either in my Cr and it didn't seem to matter much although with the 8 it seemed a bit perkier (could have been my imagination though LOL!!).

If your last piston change showed any detonation marking around the piston top I'd definatly have a bit of a squiz at the rotor & timing.

To save me a whole lot of typing I did a google I'm sure you understand this but it was good for me to have a bit of a refresh of what I read here (http://www.enginelogics.com/detonation.html)

Anyway to my untrained unskilled knowledge level, detonation = timing advance?? Possibly only a fraction out in your case?

You notice I said "you might" alot as well LOL!!! Hope this helps!

PS Your compressin is standard isn't it as High compression can cause detonation as well! Mind you to solve this I'd retard the timing a tad or lower the compression so same thing in the end.

[scott411]

yeah, what reckless, said, i would think a hotter plug would make it worse, but i am not a expert at this things,

most 250 2t's run a NGK 8 range plug, so i would stick with that

[CookMySock]

detonation = timing advance??Depends what caused it.

"Detonation" or "pre-ignition" is a widely bounced-around term, which doesn't mean much unless it is presented alongside some analysis. Detonation is the sudden and explosive burn that is associated with high combustion chamber temperatures. How that high temperature is arrived at is what needs to be examined.

If the ignition timing is too far advanced, the engine will "ping" occasionally, but usually won't enter full-blown detonation until it has been worked hard for some time, and combustion chamber temperatures have risen to such a point that the fuel/air cannot be admitted on an intake stroke without it either igniting during the inlet stroke, or igniting suddenly and uncontrollably during the compression stroke. Either way, there will be a large loss of power, and this is fully-developed detonation. Suffice to say, piston, ring, and bore damage have already occurred.

If for the above reason, or any reason, such as too-hot a plug, the spark plug electrode rises to such a high temperature, the same problem will occur. The result is identical.

If the mixture is run too lean, combustion chamber temperatures will rise also. Same result!

So there is a big difference between a little ping while goosing the throttle, and full-blown detonation - the former often but not always being tell-tale of the latter.

Steve

[B0000M]

well this is the odd thing. - its always had a 9 in it, and ive only replaced plugs when i do top end rebuilds. - eg i dont foul up plugs, they wear out.

the guy at spectrum seemed adamint that the 8 was the way to go and said it was a colder plug, but NGK's online plug code guide thing disagrees. its pretty fair to assume NGK know what theyre talking about when it comes to spark plugs.

NGK suggests going to a colder plug if detonation is occuring, but i dont think i should need to go 2 plugs colder than the factory spec of BR8.

what i think ill do at this stage is get another 9 in there. and try to figure out how to adjust the timing.

the other point worthy of note is my bike only sounds like it detonates for the first few hours after a top end rebuild. obviously due to the compression.

as i havnt owned it since new, i can only presume nothing has been altered to give it more compression. but in its current state my leg-o-meter tells me its got shitloads.


anyone know how to adjust the timing on a CR to save me having to figure it out for myself?

i presume there must be something i can turn slightly in behind the flywheel (dam shouldve looked when i had the flywheel off with the cases apart!)

[Reckless]

oh and B000m a little trick we used with the dial gauge is to get an old plug smash the porcelain and centre out braze a little bracket on whats left (ie only the steel bit and thread) to Attach the dial gauge straight to.
Then screw the the new plug bracket thingy you made into the head and mount the dial gauge to it. Nice and solid and you don't have to shag about with the magnetic stand etc. I used mine heaps of times so good to have around.

I just looked and the bracket isn't in my Dial gauge box to take a pic of for you but if you don't understand the above let me know and i"ll mock something up for you. Checking the timing is only a quick job so should be easy for you to suss out.

[Reckless]

I agree with what DB says and its all in the articles I put links to in my post.

B00m if your bike doesn't overheat easy on those big sandy hill climbs etc I think its resonably safe to assume its not got altered compression. Bearing in mind I''ve ridden with you in the past and know your running 40:1 and everything seems pretty standard with your bike.
BTW my CR never fouled a BR8 or the colder BR9 at anytime either.

The only other thing I can think of is your running really lean causing it to run hot and detonate how does your plug look after a good blast, not white or light grey/white???

Timing is easy I'll explain after you have replied.

[Danger]

I think if Boom had bothered to take any notice of my past posts on the CR250 he will have already seen that I recommend an 8 series plug and retarding the timing slightly on this bike, but how many times can you repeat yourself before it gets through? :argh:

To retard the timing loosen off the stator and turn it a penny width or an 1/8" in the direction of the motor rotation, takes about 5mins.

[camchain]

Stop starting interesting threads, I'm not getting any work done.:argh:

[chop]

Honda recomend and sell the cr250 with a 9. bit odd but i wonder if this was to try and cure detonation in the first place

[Assasin]

I think if Boom had bothered to take any notice of my past posts on the CR250 he will have already seen that I recommend an 8 series plug and retarding the timing slightly on this bike, but how many times can you repeat yourself before it gets through? :argh:

To retard the timing loosen off the stator and turn it a penny width or an 1/8" in the direction of the motor rotation, takes about 5mins.

Why do you come across as such a knob? the guy was only asking a question surprised no one has knocked you out at a trail ride the way you talk to people. Internet or not you have to remember we all bump into one another eventually.

The way you talk you would swear you are KB king u are not.

Ban me I dont care it had to be said.

[B0000M]

dangee - yea ill have a play with the timing later on. the reason ive never done anything is it only makes the noise rarely

reckless - plug colour sits at a 1970s trend brown colour.

chop - quite likely

ill also go back to a 9. no sence in running it hotter than it needs to be

[Reckless]

Stop starting interesting threads, I'm not getting any work done.:argh:

Tell me about it between being sore from Wires track and KB my weeks been shite!!!!

[Danger]

Why do you come across as such a knob? the guy was only asking a question surprised no one has knocked you out at a trail ride the way you talk to people. Internet or not you have to remember we all bump into one another eventually.

The way you talk you would swear you are KB king u are not.

Ban me I dont care it had to be said.

Dude settle down, I come across as dry but I'm sure Booom can take it, we know each other and I know he has followed previous threads where I have offered advice on this bike. Our first post to each other was giving each other shit about riding sand whoops but when we meet on the trails its a handshake and a gidday. And Booom himself is quite dry without unnecessary pleasantries in my dealings with him but its all good, we understand each other. I'm the same with Cheese when he keeps asking about his jetting on his bike, but Cheese and I get on fine as well. Don't take me or life so seriously.

[CookMySock]

I''ve ridden with you in the past and know your running 40:1 and everything seems pretty standard with your bike.That's why it's running lean and getting hot. Take it back up to 50:1. Better still, go to Amsoil 100:1.

Steve

[Reckless]

dangee - yea ill have a play with the timing later on.

reckless - plug colour sits at a 1970s trend brown colour.

chop - quite likely

ill also go back to a 9. no sence in running it hotter than it needs to be

Doesn't sound to lean then and I think you can read a plug and jet reasonably well.
You can try knocking the timing back a tad Dangers way to see how it feels.
You can't to any damage retarding it like that but mark it so you can put it back to where it was! I wouldn't want you to accidently advance it anymore than it is now!

If you want to know where your start point or factory point is you will need a dial gauge. (If you weren't far away I'd do it for you).
Mount the gauge, find TDC turn the rotor "back" from TDC to what your book says. My Ktm is 1.6mm BTDC or 17° ("Before" Top dead centre). The plug fires before the piston gets to TDC to give the gases time to explode. The mark on the stator should line up with the rotor. You will need to be able to see the gauge and the marks at the same time as due to the magnetic pull of the magnets you will need to hold onto the rotor at all times.
Its really simple and quick then you will know where factory is and you can ride it and make judgement calls from there as to what plug you want to run etc.
Re chop Comment: Better check your Manual to see if its a BR8 or 9 that's standard for that model year.

[B0000M]

Re chop Comment: Better check your Manual to see if its a BR8 or 9 that's standard for that model year.

done that, it says to use an 8.

but if it runs a 9 happily, id rather use that. cold = good in my book

[Reckless]

That's why it's running lean and getting hot. Take it back up to 50:1. Better still, go to Amsoil 100:1.

Steve

Agree with your previous comments here DB but not changing the fuel mix to fix this. Every study, track test (with computer download and analysis) and dyno test I did more oil = more horsepower. That's the rule we always went by. 20 years karting always around 25:1 and I read here that the 2smoke road race boys are running the same. So if it was lean I'd be changing the jetting not the fuel mix. But a copper brown plug doesn't sound to bad as long as its not leaning out in a particular area.

Personally I'd have a gander at the timing, I simply couldn't help myself if I where B0000M LOL!!!

Just my 2c

PS B000M I/we can only give you Internet style advice mate take it or leave it!

[Reckless]

done that, it says to use an 8.

but if it runs a 9 happily, id rather use that. cold = good in my book

OK mate I think I've given you all the opinion and advice its safe to give over the net without being there up to you what you do with it from here!

Cheers

[B0000M]

OK mate I think I've given you all the opinion and advice its safe to give over the net without being there up to you what you do with it from here!

Cheers

thanks for the advise, its more or less brought me back to what i was thinking to myself, except now i feel better about it as other people seem to think its the way too.

[Reckless]

thanks for the advise, its more or less brought me back to what i was thinking to myself, except now i feel better about it as other people seem to think its the way too.

If it where me I'd checking it out. As Danger says you might have a much better riding bike at the end of a simple timing check and adjust! But up to you!
CYA

[CookMySock]

Every study, track test (with computer download and analysis) and dyno test I did more oil = more horsepower.I submit that is because it was running leaner. The more oil you have in the fuel, the less fuel you have in the fuel, so you get more oil = leaner. You would get the same result adding more oil and jetting richer, except you would then foul heavily.


if it was lean I'd be changing the jetting not the fuel mix.I agree.

With modern 2T oils there is no reason to run 25-40:1. That is old-school thinking. We did a whole season racing a B1 on 100:1 and it was mint until it did a water pump bearing and overheated and stopped. The result was a very slight piston score.

We have the same problem with another 2T engine. We run it at 100:1 and it fourstrokes heavily and won't rev. Too rich! But if we run it on 40:1 it runs bewdy, but fouls and is hard to start. So we left it on 100:1 and rejet it, and it's mint now.

But hey, I'd say you were more experienced than I. ;)

Steve

[B0000M]

If it where me I'd checking it out. As Danger says you might have a much better riding bike at the end of a simple timing check and adjust! But up to you!
CYA

thats exactly what im planning to do. tonight hopefully

[Reckless]

But hey, I'd say you were more experienced than I. ;)

Steve

NA mate I just talk to much LOL!!!
I think us karters and possibly the road race boys have discovered what all the literature I read said that: more oil = more ring seal = more compression = more horse power and as long as your not putting so much oil in that it inhibits the combustion you get more horsepower. 25:1 was the magic figure back in those days. Then of coarse you have to jet it to run well.
Dunno really but it made sense and showed on the lap times. Sorta gave a fatter more usable power. You know, the old 10% Faster out of the corners at 50K = 10% at the end of the straight at 150K theory. Seemed to give us alot more where we needed it and didn't slow the top end at all. Leen was thin sorta power and you have to be exactly in the zone to make the most of it. when your racing other karts (or bikes) they don't let you be there. We had Micron set ups on the kart which gave top speed and down loadable track analysis as well.
But I do agree modern oils will let you run much much leaner.

Just my humble opinion though, I'm officially qualified for nothing, just quite few years karting under my belt.

[Ride it till the red]

I think if Boom had bothered to take any notice of my past posts on the CR250 he will have already seen that I recommend an 8 series plug and retarding the timing slightly on this bike, but how many times can you repeat yourself before it gets through? :argh:

To retard the timing loosen off the stator and turn it a penny width or an 1/8" in the direction of the motor rotation, takes about 5mins.

That post was all the motivation I needed, whipped downstairs and you were right, approx 5 mins to return to my seat (with a coldie too).

Just to check I've done it right; bolt top and bottom to loosen, undo screw and take off bottom plate (keep in a box to use to return to standard setting). Rotate anticlockwise slightly now that bottom plate is gone with top plate having a slot in it and tighten at required point. Yeah?

Bike has an 8 in it currently but I have a 9 that I'll take with me on Sunday when testing but I'm hoping that 5 minutes will have fixed any possible problems?

My fingers are crossed. Spent hundred upon hundred on getting it ready so far this week so it better bloody go well!

[Reckless]

That post was all the motivation I needed, whipped downstairs and you were right, approx 5 mins to return to my seat (with a coldie too).

Just to check I've done it right; bolt top and bottom to loosen, undo screw and take off bottom plate (keep in a box to use to return to standard setting). Rotate anticlockwise slightly now that bottom plate is gone with top plate having a slot in it and tighten at required point. Yeah?

Bike has an 8 in it currently but I have a 9 that I'll take with me on Sunday when testing but I'm hoping that 5 minutes will have fixed any possible problems?

My fingers are crossed. Spent hundred upon hundred on getting it ready so far this week so it better bloody go well!

Danger is the man to comment specifically on the RM but I'm not suggesting in any of my previous posts this as a standard mod to improve/change performance! I personally wouldn't move anything without the dail gauge and factory specs. The thread only went this way because B000m was suggesting the specific symptoms his bike was experiencing. This is particular to him or someone having very similar issues. If your bike is going fine don't bugger around with the timing without knowledge and the correct dial gauge etc is my personal opinion!

Jeepers I don't want everyone here ripping off to the garage and moving their stators to god knows where??
If you advance them to much by mistake you can completely shag your engine!!

[Ride it till the red]

Danger is the man to comment specifically on the RM but I'm not suggesting in any of my previous posts this as a standard mod to improve/change performance! I personally wouldn't move anything without the dail gauge and factory specs. The thread only went this way because B000m was suggesting the specific symptoms his bike was experiencing. This is particular to him or someone having very similar issues. If your bike is going fine don't bugger around with the timing without knowledge and the correct dial gauge etc is my personal opinion!

Jeepers I don't want everyone here ripping off to the garage and moving their stators to god knows where??
If you advance them to much by mistake you can completely shag your engine!!


Sorry mate should have specified, as per another thread where Danger, Booom and others gave me a bit of advice I have recently picked up an 05 CR250.... Initial test ride showed signs of detonation but was on old gas. After fixing a few other things I'm hoping to get it out for a proper test on brand new gas this weekend but thought I'd retard the timing as per Danger's advice as it seems from what I've read to be helpful with these damn honda detonation problems. Just wanted to check I'd done it correctly.

As for the RM, it's a Suzuki so it goes bloody mint! Nuff said!

[Reckless]

Shit that scared me a bit!! Saw you rode an RM and thought you where having a go at that??
I'd still want to know where factory was before changing anything if it was me but each to their own!

BTW: The warning is there for anyone else reading through this thread!!

[Ride it till the red]

From what I can tell factory is when the bottom plate is in there. If it's there it's held solid but when taken off it reveals the slot and therefore opportunity to rotate.... Obviously a bit hard to explain over the net which is why I hoped Danger would pipe back up and tell me that my suspicions were correct just to ease my mind. With this being the case I have moved it 1/8th of an inch anticlockwise (direction of motor) from standard as reccomended by Danger and in other places and therefore slightly retarded the timing and hopefully eliminated detonation. I guess we'll have to wait and see!

Cheers for the warning mate, it usually takes me a fair bit of reading and rereading before I go and change something like that so it should be ok. :confused:

[Robert Taylor]

Leaner oil ratios = richer air fuel ratio because the specific gravity of the fuel / oil mix is lighter and therefore draws through the jets more readily.
Richer oil ratios= leaner air fuel ratio because the specific gravity of the mix is heavier.
I totally disagree that more oil always = more power and can back that up with about 10 national gearbox kart titles and much more national mx titles when I was tuning / porting 2 stroke engines through the late 80s to early part of this century. During this period we had a dyno and spent many hours on it.
Our favoured oil in latter years was Motul 8002t, we ran at 40:1 ratio in 125 and 250cc mx and 30:1 in gearbox karts. Only at 30:1 in karts to preclude engine seizure when dethrottling at the end of long straights. When you dethrottle after sustained high rpm the throttle slide is shut and its predominantly only receiving lube off the pilot jet and residual oil in the system, and as the revs slowly decrease the ignition timing actually advances.
There are many causes of detonation that I will not go into here, but suffice to say retarding the ignition is sometimes a cure, as Danger said.
What is often overlooked is how our fuels are rated at the pumps, its a RON rating ( research octane number) which is a higher figure than the more important rating of MON ( motor octane number ) To confuse things further the Yanks rate as an average i.e RON plus MON divided by 2. Reading Yankee MX comics is often very misleading and their jetting specs very rarely work here because the specific gravity of their fuels and burn speeds are different.
Many 2 strokes are very marginal on pump gas. For MX we always favoured 60% avgas ( to attain a decent anti knock property, 35% 96 and 5% acteone to compensate for the lazy burn speed of avgas.

[B0000M]

[QUOTE=Reckless;1129284746
I'd still want to know where factory was before changing anything if it was me [/QUOTE]

theres also markers to line up to see where factory is. so knowing where factory is isnt a problem.


lol at removing the little plate, i went to the trouble of slotting it to get the adjustment as per the service manual... but removing it wouldve been a lot easier lol. nevermind its done now, ive used my eyecrometer to retard it a bit and will hopefully get my shifter seal and another plug before the weekend and be able to test it sat, before racing sun.

[CookMySock]

Leaner oil ratios = richer air fuel ratio because the specific gravity of the fuel / oil mix is lighter and therefore draws through the jets more readily.
Richer oil ratios= leaner air fuel ratio because the specific gravity of the mix is heavier.Yep, thats exactly what we are getting.. and thats why adding more oil leans your engine out and makes it heat and eventually detonate. More oil = leaner and hotter burn = bad!

Take your mixture up to 50:1... at least.. Your engine is probably jetted for 50:1.

Two strokes are funny with ignition timing. It's not like a 4T engine.

Steve

[Robert Taylor]

Yep, thats exactly what we are getting.. and thats why adding more oil leans your engine out and makes it heat and eventually detonate. More oil = leaner and hotter burn = bad!

Take your mixture up to 50:1... at least.. Your engine is probably jetted for 50:1.

Two strokes are funny with ignition timing. It's not like a 4T engine.

Steve

No, 100% do not agree that tuning air fuel ratio by varying fuel / oil ratio is a prudent thing to do. Most of the modern 2 stroke synthetic racing oils ( that are any good ) I wouldnt run any leaner than 40:1 in a 125 / 250cc MX bike. 30:1 in a 85. But you can run 50:1 if you are trail riding. Run 50:1 in RM125s that have notoriously weak cranks and you will foreshorten their life dramatically. Spend a little more on a modern high quality oil that burns clean but still delivers excellent lubricity e.g Motul 800, Elf and to a lesser extent the top line Castrol TTS. If you really get a kick out of constant decoking of exhaust valves then buy a cheap dirty burning oil. Cheapness is costly!!!!
If the air fuel ratio is not correct change the jets, change the needle coding! Many oem 2 stroke needles are a coding or two too rich on their taper dimensions, starting from parallell section all the way through.
Many 2 strokes out of the crate are seemingly jetted for ice racing in Canada!!!
If you are lazy and dont like changing jetting to account for varying tracks, drag created by soil conditions, humidity, altitude, oxygen concentration etc then put up with it being rich and flat. There are no free lunches if you want crisp and maximum performance.

[Danger]

Ride it till the red and Booom, I don't recall removing anything when retarding the CR250 I did, but it was a few years ago so I'm having trouble picturing in my mind what was involved, as I recall only loosening the screws, rotating slightly in the direction of the rotor spin and retighten. You don't need to move the plate much. As you can see its a very easy mod to return back to where you started. And no problems doing it to your RM250, I did just that on one slippery slimy Riverhead ride and actually went a little further than an 1/8" and liked the results, but for all other riding an 1/8" is just the right amount to smooth out the power and cure any rattle I had that wasn't fixable with jetting.

Good to see you endorse my use in the 250 of Motul 800 at 50:1 for trailriding Robert. What I feel happens is that at higher oil concentrates for trailriding the exhaust just does not burn hot enough and the muffler packing becomes soaked very quickly, but like you for MX I would run 40:1.

[Danger]

If the air fuel ratio is not correct change the jets, change the needle coding! Many oem 2 stroke needles are a coding or two too rich on their taper dimensions, starting from parallell section all the way through.


This is a very good point and as I mentioned in another thread regarding the CR250 is exactly what I suspected was part of the problem with this bike. I recall recommending to my mate that we try a different needle after never being 100% happy with the results but, well it was his bike and he sold it for a 200EXC in the end and I don't recall the specifics of which needle we were going to try.

I also did the very same thing on my 200EXC, used a completely different needle and I swap between needles on my RM250 to suit the season after never being happy with the JD needles or the stock needle for my bike.

[Ktmboy]

Yes I total agree with the ratios from Robert. Learnt the hard way with the boy on his KX85. It was laziness really that keep me using 40:1 the same as my bike(one container you see) and I didn't realise he was on the pipe so much. Lack of lubrication killed it, not how lean it was.

Hes on about 30:1 with Silkolene and I'm using 40:1 with the same even with trail riding and our pipes are very clean.

I'm 100% sure it has a lot to do with the quality of the oil. Strange though we use 91 oct and have never fouled a plug.

[CookMySock]

No, 100% do not agree that tuning air fuel ratio by varying fuel / oil ratio is a prudent thing to do.Yeah, I didn't mean to suggest that fuel/oil ratio was a useful tuning tool. I meant to observe how they were inter-related, basically agreeing with your statement.

We adjust the jetting on a race-to-race basis, but it's easy as the main jet hangs out the bottom of the carb. (pocket bike)

Steve

[Robert Taylor]

Ride it till the red and Booom, I don't recall removing anything when retarding the CR250 I did, but it was a few years ago so I'm having trouble picturing in my mind what was involved, as I recall only loosening the screws, rotating slightly in the direction of the rotor spin and retighten. You don't need to move the plate much. As you can see its a very easy mod to return back to where you started. And no problems doing it to your RM250, I did just that on one slippery slimy Riverhead ride and actually went a little further than an 1/8" and liked the results, but for all other riding an 1/8" is just the right amount to smooth out the power and cure any rattle I had that wasn't fixable with jetting.

Good to see you endorse my use in the 250 of Motul 800 at 50:1 for trailriding Robert. What I feel happens is that at higher oil concentrates for trailriding the exhaust just does not burn hot enough and the muffler packing becomes soaked very quickly, but like you for MX I would run 40:1.

1mm of stator rotation at the marks approximates to 1 degree of timing advance or retardation. You will take out midrange hit and maybe a touch of peak but also extend over-rev, the charge burns later, elevates the pipe temp and changes the speed of sound of the wave energy happening in the pipe.

For trail-riding its also about the bike not as constantly being ''on the pipe'' and therefore scavenging efficiently to give a complete burn.

Motul 800 is a very hard oil to beat, worth the extra money alone in extended crankshaft hours.

If you dyno an RM250 you will often find that the powervalve opening curve is not smooth and in total sunchronisation, there is often a noticable step in the powerband. That may have got a little better on later models. Late model YZ250s are very smooth in that respect.

[Danger]

Good info thanks.
Run a Bills Pipe with a few extra pipe gasket washers, a reed spacer (just like Ricky) standard muffler (shorty didn't help over rev) and yes I noticed when I got the bike the lack of over rev, its much better now and very smooth through out the range, very YZ like and great for offroad use, perhaps a dyno would show different.

[cheese]

Hmm I'm about to run out of TTS, and I used to use Motul 800, but went for TTS because its more easily available. Currently running 40:1 with a 8exv (I think it is) plug. My jetting is standard and I want to have a play with it, but to be honnest its running pretty good, but I'm sure it could be fine tuned.

[Reckless]

Yeh Robert generally I agree with you and must qualify my "More oil = more Hp" comment. It was with reference to the 100:1 mixes being put forward as a ratio for fuel mix. I was implying that in my opinion you'd get more HP at 25, 30 or 40:1 than 100:1. But any sane person would realise there is a point where you get to much.
Interesting your where running 30:1 in the gearbox kart, we where at 25:1 so not to far off your premium mix. But our compression and timing could have been different as well. We always run motul and I still do. Some guys where 60-80:1 though. LOL you must have read my plug a million times when I was travelling everywhere with Geoff Downs but kept your ratios pretty close to your chests LOL!! Mind you not many people could beat the great Ian Bias and Rimmer in those days he was certainly king of the gearbox class for many years!

Interesting you say 50:1 for trail riding my manual specifies 60:1 in the Ktm200exc. But I'm running Motul at 40:1 and its not perfectly tuned for max performance. But I'm happy with the amount and way it delivers its power. Doesn't drip oil outa the exhaust or foul plugs and delivers as much smooth power as I can handle so at my level of riding thats good enough! The 200 probably revs out more like a 125 than a 300 anyway so i definatly agree as I have previously said, tuning is way better than varying the fuel mix to cure any issues so I'll stick with my 40:1 I reckon, seems a good happy medium for the odd occasion when I go to Harrisville or Ardmore.

Interesting thread! Who'd have though a simple Spark plug question would lead all the way here LOL!!!

[Danger]

Reckless we were talking 250's with relation to the 50:1 ratio for trail riding using Motul 800.

Personally I also use 40:1 on the 200 so I think your all good.

[camchain]

Feeling more & more comfortable about moving to Motul 800. Reckless using it plus pics of stripped down engines (on KTMtalk.com) looking super clean and good nick prompted me to trying it. Reckless, I knew where you were coming from re oil mix!

[vifferman]

I think us karters and possibly the road race boys have discovered what all the literature I read said that: more oil = more ring seal = more compression = more horse power and as long as your not putting so much oil in that it inhibits the combustion you get more horsepower.
There's another aspect to this (something I learned from a mate who used to race an RD350). Using more oil allows you to run slightly more advanced ignition and/or more compression, as the oil effectively increases the octane rating.

[xen]

Some good info here guys, thanks.

Re Motul 800, I've switched to it too and using at 50:1. Found it for $100 for 4L at http://www.usprocurements.co.nz/

[Sammikins]

Some good info here guys, thanks.

Re Motul 800, I've switched to it too and using at 50:1. Found it for $100 for 4L at http://www.usprocurements.co.nz/

Love US procurements, bought a few things off them! :Punk:

[honda_power]

i got 4l for $98 from boyds

[Robert Taylor]

There's another aspect to this (something I learned from a mate who used to race an RD350). Using more oil allows you to run slightly more advanced ignition and/or more compression, as the oil effectively increases the octane rating.

I wouldnt treat that as gospel.

[Robert Taylor]

Feeling more & more comfortable about moving to Motul 800. Reckless using it plus pics of stripped down engines (on KTMtalk.com) looking super clean and good nick prompted me to trying it. Reckless, I knew where you were coming from re oil mix!

We always used this oil in Hurleys Yamahas, even though we were runing other stickers. It doesnt matter how free the oil is, if it causes issues dont use it.

[flyingcr250]

i got 4l for $98 from boyds

i used to get 4L of tts from boys at a real sharp price. oops ive gone off topic again:Offtopic: ha ha sorry

[camchain]

We always used this oil in Hurleys Yamahas, even though we were runing other stickers. It doesnt matter how free the oil is, if it causes issues dont use it.

You've piqued my curiousity with that one.
Edit: Think I might have guessed. Reading between the lines yr post and some anecdotal stuff I've just been reading.

[tommorth]

Interesting stuff might change from tts haven't much of it left anyhow and if I change from 32:1 to 40:1 it'll probably work out cheaper.

Danger any chance of letting me know where your at with your jetting for your 200?
Be interested to compare mine is 42p 188m 1.5a/s cek on 2nd clip from bottom 32:1 runs good with this, a little spooge but not much needle could probably drop one but is more tractable as it is. Bikes stock bar carbon reeds and a reed spacer.

Any thoughts on whether the iridium plugs are worth the extra cost? They are often speced from factory but do they actually make a noticeable difference.

[camchain]

I had the impression iridium plugs were more prone to fowling due to fine electrode, but maybe opposite true if better spark? Used them in my $ stroke as recommended as part of stage 2 mods.

[Danger]

Interesting stuff might change from tts haven't much of it left anyhow and if I change from 32:1 to 40:1 it'll probably work out cheaper.

Danger any chance of letting me know where your at with your jetting for your 200?
Be interested to compare mine is 42p 188m 1.5a/s cek on 2nd clip from bottom 32:1 runs good with this, a little spooge but not much needle could probably drop one but is more tractable as it is. Bikes stock bar carbon reeds and a reed spacer.


Your clip position is known as CEK4.

I'm running very similar at this time of year CEK3, 188, 42, AS 1 7/8 aprox, Motul 800 40:1 BP Ultimate.

When I run 32:1 I run CEK4 in winter so looks like your bang on with just AS tuning for the day.

This assumes you have a pre '07. They changed the carb to a smaller 36mm after that from memory and optimum jets will change.

These settings get too rich once temps get up to 18 degrees or beyond.
Then I switch to summer settings of CEK2, 185, 40, AS 1 1/2 aprox.

[tommorth]

thanks interesting to see that our jetting is very similar . Bike is a 2000 so still has bigger 38mm carb has had airstryker put on at some point, think fitted from 02 not sure.

I was running a 40 pilot cek3 and 185 main in summer. good to know that I won't be far off when i change ratios