Bike slower when up to temperature, faster when cold.

[racefactory]

Hey guys,

It's not a problem as such, but I have noticed that when my NC30 is up to temperature (85 onwards) it is slower at the low rpms. It just does not have that punch and the front end doesn't quite feel so light under full power. Sounds slightly different too, maybe a tad more 'boggy'. I'm not sure about the difference over 10K rpm though, think it's fine then.

This is not to say that I full throttle it whilst completely cold but once it is at 70 degrees (gettting warm) it definately has more punch and power at the lower rpm ranges. It's no problem as such, but it's enough so that when its in the 70's... it really makes me smile under full power, not so much when up to temp.

This bike has had ER10EH plugs instead of ER9EH plugs. Last owner said it's better for high speeds/high revs. That's all I can think of mechanically.

It is the 92 model so bigger jetting from the 89 model.

Any idea what I can do?

Sounds like jetting/carb thing... but I won't say any more. Air filter? Shit I don't know...

[CookMySock]

This engine is EFI ? If it is, then will will be richened right up when its cold, and leaned out as safe as possible towards stoich when its warm, for cleanliness and economy. So yeah you are probably right - maybe its a little lean.

IF this this the problem, you can put a variable resistor on the water jacket temperature sensor and 'fool' the computer into thinking it's colder than it really is, and it will keep it slightly richer for you. Of course you could fuck the engine completely playing with this stuff too, so YMMV.

My ol' skyline was the same - bags of omph while she was warming up and a little laggy while warm. It had a worn throttle body - was leaking air in around the spindle, so maybe you have a similar leak. It also had a big dead spot when warm.

Alternatively there might be a simple fault elsewhere.


DB

[Tank]

This engine is EFI ? If it is, then will will be richened right up when its cold, and leaned out as safe as possible towards stoich when its warm, for cleanliness and economy. So yeah you are probably right - maybe its a little lean.


ummm - if its being 'leaned out towards stoich' then its still rich - you have to have a mixture that is GREATER then stoich for it to be lean.

Dangerous mechanic...

[racefactory]

Lol. No don't think it's lean. Boggy acceleration is not a sympton of lean mixture as far as i know.

No it's not fuel injection it's an NC30.

Thanks.

Another thing to note- when it's up to temp, when you slam on the throttle full blast it is worse, engine note changes to a more burbling, boggy kind of sound. If you roll on the throttle, it seems to be better, still not the best but bit better. So basically you just can't make the revs climb too fast otherwise it will go rich.

I think i've pretty much answered my own question in terms of what's wrong? But it's just a stock bike, what could be causing this?

I've never looked at the air filter, and they are harder than most bikes to get to (like every simple maintenance task on these bikes) so that's why. Don't know if that could cause this though as when it's getting warmish it goes liek hell.

[mowgli]

Another thing to note- when it's up to temp, when you slam on the throttle full blast it is worse, engine note changes to a more burbling, boggy kind of sound. If you roll on the throttle, it seems to be better, still not the best but bit better. So basically you just can't make the revs climb too fast otherwise it will go rich.

Sounds like an ignition timing issue to me. When you open the throttle rapidly the timing should advance. I expect the NC30 has electronic ignition so check the wiring around the carbs and inlet manifold. You might find the plug to the vacuum sensor or throttle position sensor is loose.

[riffer]

Sounds like you've got worn jet needles.

[racefactory]

ok took the air filter out and had a look... doesnt look that dirty to my eyes but it's the first time i've seen one anyhow. Don't understand how the machine can actually suck any air through that series of sponges though. Don't know how much oil is supposed to be on the sponge either. Shall I try running it with only the little sub air filter element in place? Shall I just put some pantyhose or something over the main air filter gauze and run it as opposed to having that thick sponge blocking the air and see if that makes it better?

I don't understand how it's electronic issue as it goes like a raped ape in cold weather/ warming up engine temperatures.

needles- yes well the problem is at low rpms, suggesting the needles but then again... it runs like a raped ape when it's cold and wouldn't a worn needle jets be shitty when in colder temperatures too?

Surely it's to do with air flow since air is less dense when warm?

One thing to remember here is that it's not exactly a problem in a 'problem' sense lol, it's just something i've noticed... it still goes like mad when it's warming up. It's just I only get, say 10 mins of real good fun before it gets slower and less punch.

apparently fuel tank breather can affect mixture, is that true? What if i run it without that?

[mowgli]

I don't understand how it's electronic issue as it goes like a raped ape in cold weather/ warming up engine temperatures.

Resistance increases with temperature. If a plug is only making partial contact then there might be little effect at colder temps but as the engine warms up the resistance across the partial contact might override the resistance in the sensor.

[racefactory]

Shall I try running it with only the little sub air filter element in place? Shall I just put some pantyhose or something over the main air filter gauze and run it as opposed to having that thick sponge blocking the air and see if that makes it better?

apparently fuel tank breather can affect mixture, is that true? What if i run it without that?

Please! Have no idea if it's that bad to do that or not..

I've also learnt that there is absolutely no way for cold air to get into this air box on these! There are no tubes or any passageways to feed fresh cold air in. The intake for air filter is in a little enclosure where i presume it's just going to to be sucking in all the really hot air that these bikes produce in the frame.

I've seen a lot of bikes have pipes from the front or some sort of ram air system. Surely i'm not the only NC30 owner who's seen this performance drop then?

[hayd3n]

clean your plugs give it a oil and air filter change

[lostinflyz]

two things. those #10 plugs will foul out in about 30 seconds. there absolute cunts. ive gone through about 4 sets on my race bikes and there crap. use the 9's when u replace them.

sounds like the carbies are outta synch a bit. my old nc30 used to struggle like a mad bastard when u cracked the throttle fast. either that or you may have a slide thats sticky or not working properly.

best advice is check/clean/change the plugs and see how she goes. if that fails a big ol carby clean and synch session is in order.

another thing. why do you have 2 air filters???

anyway cant see a fuel breather effecting mixture outside possibly causing fuel stavation but thats not a mixture problem.

the stock airbox is pretty crappy but playing with it can be alot more pain than its worth. HRC did a scoop that collected air from forward of the top radiator but its not really ram air. just remeber that these vacuum carbies are a weee bit picky about air flow and all the like. but anyway drifting off topic.

[racefactory]

two things. those #10 plugs will foul out in about 30 seconds. there absolute cunts. ive gone through about 4 sets on my race bikes and there crap. use the 9's when u replace them.

sounds like the carbies are outta synch a bit. my old nc30 used to struggle like a mad bastard when u cracked the throttle fast. either that or you may have a slide thats sticky or not working properly.

best advice is check/clean/change the plugs and see how she goes. if that fails a big ol carby clean and synch session is in order.

another thing. why do you have 2 air filters???

anyway cant see a fuel breather effecting mixture outside possibly causing fuel stavation but thats not a mixture problem.

the stock airbox is pretty crappy but playing with it can be alot more pain than its worth. HRC did a scoop that collected air from forward of the top radiator but its not really ram air. just remeber that these vacuum carbies are a weee bit picky about air flow and all the like. but anyway drifting off topic.

This is the kind of answer I'm looking for- thanks.

Thing is, my idle is very smooth, the engine sounds smooth and solid... I've heard that when carbs are out of sync the bike looses that. The bike feels nice and solid still... just not as powerful.

For how much it costs to sync the carbs, I don't think it's worth it if the cause is not confirmed... i got quoted for absolutely hundreds of dollars...

Maybe i should squirt some of the ''carb cleaner'' down the air intake holes??

Anooying me more day by day! Keep it coming guys... cheers.

Also... what do you mean exactly by 'foul out'? I don't have any miss fires or any trickery with them as far as i can tell.

I don't have a fucking tool to get the spar plugs out which is very annoying... my standard spark plug socket does not work on these tiny fuckers. Anyone know what size socket i'm going to have to fork out for?

[quickbuck]

Getting a carb balance is always worth it.
Will cost a little bit, but at least all 4 cylinders will be doing the same thing once it's done.

Not sure of your plug size,, sorry, but as said, get rid of the 10's asap. They are way too cold.
It could be even a case of one fowling after a period of time that is causing it to be sluggish when warm....

[lostinflyz]

you can synch the carbs urself if your patient (or cheap)

those 10 plugs are a nightmare,they work for a while but they certainly dont last.

that carby cleaner shit is pretty useless. you really gotta pull the carbs and properly clean everything.

cant rem the spanner size (maybe 3/4"). theres a nc30 tool kit online cheap thatd prob be worth it.

[racefactory]

oh shit forgot about the tool kit i've even got it!

yes carb sync,.. i was talking to a guy who said that may well be it. I tried at honda and they said something fucking rediculous like 800 bucks...

where shall i go to get them synced?? Can anyone here do it for me (paid of course) ?

Yes thanks for the advice i shall have to get some 9's...

[racefactory]

It could be even a case of one fowling after a period of time that is causing it to be sluggish when warm....

excellent mate thanks... i've realised it is quite sudden when it looses that 'bite'. I think this is what i need- simply new plugs and balance. Fuck knows where i'm going to get a balance from though...

[quickbuck]

...... they said something fucking rediculous like 800 bucks...
...

Yep, that is very ridiculous!
Okay, the room in the VFR is tight, but heck.... not $800 tight!

Bound to be somebody around who can help out.

[lostinflyz]

yea ive hadthe same bullshit from our local honda dealer before.

as i said its not too hard to doon your own but anywhere that does m/cycle tuning should be able to do it. i do know some places often refuse to do the v4's but someone'll do it.

[PirateJafa]

...they said something fucking rediculous like 800 bucks...

That's pretty much their way of saying they don't want to do it.

[lostinflyz]

That's pretty much their way of saying they don't want to do it.

haha yea and that was the polite way. I went to get mine done and they charged me 100 bucks and then told me that eveything in the carbies needed replacing which was gonna be 1200 bucks.

Took the bike home and took the tank off. the wee marker i left on the air box hadn't moved so they never even took the carbies off. thats what you get when you go to CASBOLTS!!!!

[racefactory]

where's casbolts?

[lostinflyz]

Christchurch.

see if you can find a dyno tuner. usually they do it or know the best guys to do it.

[sir]

Ive got an nc21 and im pretty sure the socket size for the plugs is a dirty old 16mm . I dont think panty hose will do it any justice as I went for a blat up the road on mine with out a filter and too much air just made it die when i tried to give it a fistfull . Maybe you clould look at your cooling system , it might need a flush and some coolant .

[Rob Taylor]

Change your plugs,thats easy......Dont think it will be carbs, Could be a spark issue though as in lack of.Before you change plugs ,pull them out and check the gaps..Rule of thumb is thickness of a hack saw blade ..Close the gaps up so they are closer than normal (which allows spark to jump if you have weak spark),reinstal and take for a run ,see if it still does it,,,,If it runs perfect, check coils>>>> If no better back to drawing board..Good luck

[racefactory]

excellent thanks. I'll try that taylor.

Oh and i ran it without the main air filter element... not much difference really, maybe a tad quicker but its probably just me.

Yes if you roll on the throttle and don't beat the engine to the revs its good, just when it's warm, and you grab full throttle from low revs it will change engine tone and sound mushier and accelerate slower.

Hopefully it's a plug problem!

By the way... when you guys were talking about 'fouling plug' , what do you mean exactly? Because i have not felt any misses or more extreme behaviour, don't know what this is...

THANKS

[quickbuck]

2 Strokes are renowned for fouling plugs, but it can happen on 4's as well.

What happens is that plugs are designed to be a certain heat range to stop them causing pre ignition. This is when the base of the plug glows red hot, and ignites the fuel air mixture on the compression stroke... well before the charge provided by the coil gets a chance.
As you can imagine this is BAD.

Anyhow, conversely if they are too cold, then the fuel air mixture doesn't ignite properly, and the base of the plug gets wet with fuel. On a 2 stroke remember there is an oil component in there to make matters worse.

As the VFR is obviously a 4 stroke, it is the fuel wetting the base of the plug, and then it can't do it's job properly. Obviously the longer it runs without igniting the charge, the wetter it gets..... Then sluggish motor.

On a four cylinder, the other three will help a bit... but it will sound like a Subaru... Well the IL4's do, a VFR... Well, yep, it will sound crap. It may just die off, and you don't really notice, apart from a lack of acceleration... Or, willingness to rev.

So, long story short, run the recommended heat range for the motor, unless it is severely tweaked, and you have an issue with pre ignition....

Hope this helps.

And anybody, if I'm slightly misguided in anything, please let me know.
It has been a while since i have done Reciprecating engine theory.

[xwhatsit]

Yes if you roll on the throttle and don't beat the engine to the revs its good, just when it's warm, and you grab full throttle from low revs it will change engine tone and sound mushier and accelerate slower.
Sounds like standard slide carb behaviour, do you know if it's got slide carbs or CVs? You come from two strokes, too, don't you? They're far more responsive like that than four strokes, four strokes have to be babied with the throttle a bit more otherwise they will gasp and take a while to catch up when you crack open the throttle too quickly. CV carbs mitigate this a lot, s'why they're fitted to most modern bikes, but they've got their own set of problems.

I dunno what the problem is with finding a plug wrench, they're NGK E, right? Just get an E-sized plug wrench. I suppose there is that whole watercooled four-cylinder thing where you need a plug wrench the length of Sarah Jessica Parker's face.

[racefactory]

Yes I'm really really hoping its fouled plugs now! Sounds right.

Na I just couldnt find a right sized plug wrench when i had it all apart... i'll get one of those... the problem now is just these $50 DOLLAR EACH spark plugs.

[limbimtimwim]

the problem now is just these $50 DOLLAR EACH spark plugs.After shipping this might work out cheaper: http://tyga-performance.com/site/product_info.php?currency=AUD&cPath=72_83_153&products_id=886

My NC35 is the same. Much happier when it's cold. It always feels better riding it on a cool night.

Do you still have the heat shield in place between the airbox and the fuel tank?

[racefactory]

Yeah thanks i was thinking of getting from TYGA.

What about those 8's, as opposed to 9's??

[sinfull]

Been near a week now Trademe tut tut ! Go buy some new 9's chuck em in and if that dont fix, ride in a higher rev range till ya can afford to do ya carbs !

[klyong82]

Yeah thanks i was thinking of getting from TYGA.

What about those 8's, as opposed to 9's??

Hmm the 8's are hotter plugs so would be more suitable for communting in warm temperatures while the 9's cooler plugs perform better for touring or high performance bikes (1000cc etc).

[racefactory]

Ok just about to make the order from the UK... 90 bucks for a set including shipping, absolute cheapest i could find lol!

[The Pastor]

Sounds like jetting/carb thing... but I won't say any more. Air filter? Shit I don't know...


This engine is EFI ? If it is, then will will be richened right up when its cold, and leaned out as safe as possible towards stoich when its warm, for cleanliness and economy. So yeah you are probably right - maybe its a little lean.

IF this this the problem, you can put a variable resistor on the water jacket temperature sensor and 'fool' the computer into thinking it's colder than it really is, and it will keep it slightly richer for you. Of course you could fuck the engine completely playing with this stuff too, so YMMV.

My ol' skyline was the same - bags of omph while she was warming up and a little laggy while warm. It had a worn throttle body - was leaking air in around the spindle, so maybe you have a similar leak. It also had a big dead spot when warm.

Alternatively there might be a simple fault elsewhere.


DB

are you always this stupid or are you just trying harder today?


ok took the air filter out and had a look... doesnt look that dirty to my eyes but it's the first time i've seen one anyhow. Don't understand how the machine can actually suck any air through that series of sponges though. Don't know how much oil is supposed to be on the sponge either. Shall I try running it with only the little sub air filter element in place? Shall I just put some pantyhose or something over the main air filter gauze and run it as opposed to having that thick sponge blocking the air and see if that makes it better?

I don't understand how it's electronic issue as it goes like a raped ape in cold weather/ warming up engine temperatures.

needles- yes well the problem is at low rpms, suggesting the needles but then again... it runs like a raped ape when it's cold and wouldn't a worn needle jets be shitty when in colder temperatures too?

Surely it's to do with air flow since air is less dense when warm?

One thing to remember here is that it's not exactly a problem in a 'problem' sense lol, it's just something i've noticed... it still goes like mad when it's warming up. It's just I only get, say 10 mins of real good fun before it gets slower and less punch.

apparently fuel tank breather can affect mixture, is that true? What if i run it without that?

I would do this

- change the plugs.
- remove airfilter [not the air box] and run with out it (just to test it)
- get the carbs balanced
if it still running werid i'd see about new needles or a dyno tune.

FYI you can buy air filter foam and cut your own filter to fit - you oil them with 2 stroke oil (cheapest you can get) and you put on sparely - no excess oil

[racefactory]

yeah I agree- well hopefully plugs solves it.

Yeah i don't know what the dude was on about earlier lol!!!

[lankyman]

Lol. No don't think it's lean. Boggy acceleration is not a sympton of lean mixture as far as i know.

No it's not fuel injection it's an NC30.

Thanks.

Another thing to note- when it's up to temp, when you slam on the throttle full blast it is worse, engine note changes to a more burbling, boggy kind of sound. If you roll on the throttle, it seems to be better, still not the best but bit better. So basically you just can't make the revs climb too fast otherwise it will go rich.

I think i've pretty much answered my own question in terms of what's wrong? But it's just a stock bike, what could be causing this?

I've never looked at the air filter, and they are harder than most bikes to get to (like every simple maintenance task on these bikes) so that's why. Don't know if that could cause this though as when it's getting warmish it goes liek hell.

If you pull out the air filter you will see at the front of the air box there is a little rubber flappy thingy that the air has to force it's way around to enter the airbox. If you remove this peice (cut it off) you'll notice you get better throttle response and it won't try to die when you blip the throttle at idle. I've read reports about this causing a pressurisation of the intake but mine has never run better since carrying out this small mod. Also replace the crappy paper filter if this hasn't been done already.

[lankyman]

yeah I agree- well hopefully plugs solves it.

Yeah i don't know what the dude was on about earlier lol!!!

And with plugs being 50 bones a piece, I'm sure this is worth a try beforehand.

[racefactory]

If you pull out the air filter you will see at the front of the air box there is a little rubber flappy thingy that the air has to force it's way around to enter the airbox. If you remove this peice (cut it off) you'll notice you get better throttle response and it won't try to die when you blip the throttle at idle. I've read reports about this causing a pressurisation of the intake but mine has never run better since carrying out this small mod. Also replace the crappy paper filter if this hasn't been done already.

Wow ok, will have to check this out when i get it all apart again when the plugs arrive... Swear i never saw such a thing in there. Surely you'd think Honda would know the best?

[niero]

Its completely normal (up to a certain degree depending on the engine design). Engine performance decreases with drop in HpA (Air Pressure) and temperature. This is truly visible when you fly helicopters. On some days you will not be even able to lift of due to the humidity, and the temperature of air. When the air is colder its also denser. Therefore, if the bike is getting too hot and the air takes time to get in to the engine (depending on the construction of the engine) the air may become less dense (aka less air per fuel ratio) and a RICHER mixture will occur. This will result in power loss and lead deposits in the spark plugs (spark plugs fouling), if the mixture is too lean though, this is by far worst case scenario, things like Pre Ignition and Detonation may occur, very bad for the engine, also if you see that you Cylinder Head Temperature is going through the roof (I doubt you have that instrument but I'l keep going anyway) this is a sign of mixture being too lean. The new engines have CDI's instead of Magnetos, I am not sure what you have but if it is the cdi, the following may also be occurring. in semi conductive circuitry a rise in temperature will increase the resistance in the wire, but will decrease the resistance in your resistors. The resistors serve two purposes (usually), to limit the current and to get rid of the heat. If its resistance is dropping it will mean that it will also become inefficient at getting rid of the heat. Therefore the microchip inside your CDI is getting a bit hot, and sometimes at certain points may shutdown due to heat shock. Dont panic thats ok, most new chips nowdays just shutdown when they are too hot and come back online when they are cool again. in your case its might be just a couple of pins, try giving the CDI some vent, see what happens!

[xwhatsit]

When I had trouble getting a good fat blue spark, this effect used to be very noticeable on my bike. Now it's less obvious, presumably because now with great spark I'm getting good combustion every time even if it's hot (so the mixture is not optimal or whatever is going on). But sometimes, when you wake up really early before it gets light, hunched over the tank down the hill into Kawakawa Bay, you can feel the engine crackling and howling like it never does normally. It loves the cold air, engine feels crisp and sharp. My father reckons it's a thing air-cooled bikes do, but I dunno about that. My guess is carburettion vs. EFI.

[racefactory]

Interesting.

Yes, must be just all carb engines to some extent.

niero... how can I tell if my cylinder head is too hot- what kind of reading should i be expecting?

[niero]

Absolute Max 140 C.Well, here is where you need a sender unit mounted into the cylinder head. Much like your water temp it will be connected to a sender terminal and will transmit the temperature on to a gauge. But this occurs only when too lean mixture is present, when I had an other look at you issue I dont think the mixture is too lean but rather too rich. Are there any carbon deposits anywhere on the spark plugs or anywhere else? A good way to test if its your intake is to go in a 60-70km/h area where you are in your last gear but doing not too many revs, and give it some gas, (when running hot) if she goes well then its your intakes, if not then again it might be Mixture Setting. For the reasons I have stated above the air will be less dense and therefore when ignition occurs there is not enough air to ignite all the mixture (Fire needs oxygen). The only way to overcome that is to ventilate your bike better, get a better radiator unit or make the air intake bigger, maybe even mount a fan in it (talk about "old man's turbo) Good Luck!

[lankyman]

Wow ok, will have to check this out when i get it all apart again when the plugs arrive... Swear i never saw such a thing in there. Surely you'd think Honda would know the best?

Yea you'd think so aye....

[lostinflyz]

Yea you'd think so aye....

mwahahaha by the time youve made it through the manufacturing and budgeting department any good thoughts they have are stripped bare and only the bare essentials left, that were the cheapest, easiest and fastest to make.

however its quite common for guys to modify the airbox on these. so it may never have been there. honda makes motorcycles to last forever and considering jap restrictions on 400cc motorbikes thay could be pretty conservative with the airbox.

[racefactory]

mwahahaha by the time youve made it through the manufacturing and budgeting department any good thoughts they have are stripped bare and only the bare essentials left, that were the cheapest, easiest and fastest to make.

however its quite common for guys to modify the airbox on these. so it may never have been there. honda makes motorcycles to last forever and considering jap restrictions on 400cc motorbikes thay could be pretty conservative with the airbox.

What are some mods for the air box?

Do you have any opinion on the TYGA 'race air box' that claims more volume?