RGV250 Race bike jetting

[7mmWSM]

Ok, only want to hear from people with actual experience in tuning a race spec RGV.
Bikes running no filter or lid and and I've richened up the jetting but can't get rid of a splutter at 8000rpm when you roll on the throttle from closed position.

Plugs look good - nice and dry and coffee colour.

Interested in knowing if anyone knows approx what jetting to be running at Manfeild?

[Sensei]

Could be wrong here but I would say the fact the bike doesn't have a filter or lid would be a good reson why its not running well apart from this been bad for the motor not having anyway of filtering the air going straight into the motor . Is there a reson you have taken them out ??

[imdying]

Which model? Which carbs? What solenoid plumbing? www.rgv250.co.uk is a better bet.

[7mmWSM]

Could be wrong here but I would say the fact the bike doesn't have a filter or lid would be a good reson why its not running well apart from this been bad for the motor not having anyway of filtering the air going straight into the motor . Is there a reson you have taken them out ??



Ok, only want to hear from people with actual experience in tuning a race spec RGV.

its set up to get every available HP out of the motor

[koba]

Ok, only want to hear from people with actual experience in tuning a race spec RGV.


You can say it but yopu aren't likely to be that lucky!

tried rgv250.co.uk or similar?

Would a flat spot there affect you in a racing situation?

EDIT: haha, I was too slow!

[7mmWSM]

You can say it but yopu aren't likely to be that lucky!

tried rgv250.co.uk or similar?

Would a flat spot there affect you in a racing situation?

EDIT: haha, I was too slow!

Well I thought I might get lucky as i'm kinda running out of time till the weekend.
it could affect getting on the gas mid corner.
I got the kit manual off that site but recommended jetting they list is way too rich i've found

[RDjase]

Well I thought I might get lucky as i'm kinda running out of time till the weekend.
it could affect getting on the gas mid corner.
I got the kit manual off that site but recommended jetting they list is way too rich i've found

What model rgv and what carbs , 32mm or 34mm

[eelracing]

Don't discount Senseis' suggestion out of hand just yet coz RGV's (or any engine in fact)don't like sucking in heated air flowing in from engine/radiator and by removing the airbox lid you are encouraging this...especially bad with the RGV too.Some have even raised the tank to encourage cooler air in.
Shrouding of some sort can help here.

I'm running Tyga pipes,standard airbox,34mm carbs and std mains.Also should mention i'm getting out dragged by 2 fookn NSR's so would be keen on seeing how your mods are working this weekend.But not to keen,if ya know what i mean haha.

But when it starts bogging/spluttering does rolling off of the throttle slightly improve fueling?
You say just as you are rolling on the throttle so i'm presuming up to 1/4 opening which basically means you should be looking at the air jets and possibly needles.

[7mmWSM]

What model rgv and what carbs , 32mm or 34mm

34mm carbs

[7mmWSM]

Don't discount Senseis' suggestion out of hand just yet coz RGV's (or any engine in fact)don't like sucking in heated air flowing in from engine/radiator and by removing the airbox lid you are encouraging this...especially bad with the RGV too.Some have even raised the tank to encourage cooler air in.
Shrouding of some sort can help here.

I'm running Tyga pipes,standard airbox,34mm carbs and std mains.Also should mention i'm getting out dragged by 2 fookn NSR's so would be keen on seeing how your mods are working this weekend.But not to keen,if ya know what i mean haha.

But when it starts bogging/spluttering does rolling off of the throttle slightly improve fueling?
You say just as you are rolling on the throttle so i'm presuming up to 1/4 opening which basically means you should be looking at the air jets and possibly needles.

Yes we will find out this weekend!

Current jetting is

360/370 mains
27.5 Pilot
#55 needle in 2nd position
0-9 needle jet
0.7 PAJ
0.5 MAJ



I will try dropping the Needle jet down to 0-8 and I think I have spare 0.5 PAJ that I will try.

My Airbox has been modified to draw in cooler air with a heat sheild between it and the motor.

[CookMySock]

I have a couple of 2T pocketbike race engines (18k redline), and that mid-range falter usually means it is set a tad too lean. One of my bikes has an adjustable main jet, and a verrry slight tweak towards rich should clear it up.

Unloaded, from idle, if you full-throttle blap it, does it instantly rev hard and cleanly or does it slightly falter? If it falters every so slightly, then richen just the smallest amount.

Steve

[SS90]

Yes we will find out this weekend!

Current jetting is

360/370 mains
27.5 Pilot
#55 needle in 2nd position
0-9 needle jet
0.7 PAJ
0.5 MAJ



I will try dropping the Needle jet down to 0-8 and I think I have spare 0.5 PAJ that I will try.

My Airbox has been modified to draw in cooler air with a heat sheild between it and the motor.

It's unlikely that anyone will give you magic numbers on the net, but as a matter of interest, you say "set up to get maximum power from the engine" that's a risky statement.

What sort of expansion chambers do you have?

It's an important question.

[That Guy]

I raced a RGV for a number of years and played with lots of settings. In the end I went for 5hp less than max to go for reliability (good tyres and suspension counts for lots!) meaning I ended up back with a thin filter and the air box lid for example, 30:1 and slighty dark plugs etc etc. I did cut out big holes though in the lid for a bit more breathing, and also had a heat sheild.

Regarding jetting, I agree with some responses, you won't get majic numbers on the net - each bike seems to be a little bit different, and also humidity and air pressure affects it all to. you need to sort jetting out in the real world in the end. I did settle on a main jet and pilot though for Taupo/Pukekohe/Manfeild and just moved clip positions so will see if I can find those out for a baseline if it is any use. I had a full arrows exhaust, plus a port and polish with lightened crank, so a fairly tuned engine.

Hesitation at 8000 rpm might not be jetting though if the plugs are a nice colour - the ignition on my bike did some wierd things cuasing random rpm blips, only sometimes. It drove me nuts trying to find it, in the end I systematicall replaced the whole ignition in turn - and it was the picks up causing the issue. I got a new set of them and viola - SV650 beater was back (in the corners anyway:clap:)

[blackstars_10]

I raced a RGV for a number of years and played with lots of settings. In the end I went for 5hp less than max to go for reliability (good tyres and suspension counts for lots!) meaning I ended up back with a thin filter and the air box lid for example, 30:1 and slighty dark plugs etc etc. I did cut out big holes though in the lid for a bit more breathing, and also had a heat sheild.

Regarding jetting, I agree with some responses, you won't get majic numbers on the net - each bike seems to be a little bit different, and also humidity and air pressure affects it all to. you need to sort jetting out in the real world in the end. I did settle on a main jet and pilot though for Taupo/Pukekohe/Manfeild and just moved clip positions so will see if I can find those out for a baseline if it is any use. I had a full arrows exhaust, plus a port and polish with lightened crank, so a fairly tuned engine.

Hesitation at 8000 rpm might not be jetting though if the plugs are a nice colour - the ignition on my bike did some wierd things cuasing random rpm blips, only sometimes. It drove me nuts trying to find it, in the end I systematicall replaced the whole ignition in turn - and it was the picks up causing the issue. I got a new set of them and viola - SV650 beater was back (in the corners anyway:clap:)


I just spoke to one of my mates that used to race one and work on them about your post. 'that guy' = great post. As he mentioned, the internet jets are a just good starting point for similar mods. The needle is absolutely key (clip position).
With regards to the airbox, my mate said that best reliable power was made with just slightly enlarged inlet holes (from 32mm to 34mm-tho some go to 36mm). Open airbox=big power=less reliability=big bang.

He also said that rgvs powervalves open 500rpm too early and give a dip in power curve around 8000rpm(on tacho). The best solution is to get an aftermarket unit and make the PV's open 500rpm later. Manual adjustment of PV does not work. His last word of advice was that best results are obtained with only a slightly modified engine with well sorted suspension ans tyres (as 'that guy mentioned also).

Jetting is based on throttle position-not revs (if its always at certain revs, then the issue is elsewhere. Put tape round the throttle and label positions (1/8, 1/4, 1/2) then use these to help with jetting. A good tip

Take it or leave it, but I usually take his advice and have only good results

[7mmWSM]

I just spoke to one of my mates that used to race one and work on them about your post. 'that guy' = great post. As he mentioned, the internet jets are a just good starting point for similar mods. The needle is absolutely key (clip position).
With regards to the airbox, my mate said that best reliable power was made with just slightly enlarged inlet holes (from 32mm to 34mm-tho some go to 36mm). Open airbox=big power=less reliability=big bang.

He also said that rgvs powervalves open 500rpm too early and give a dip in power curve around 8000rpm(on tacho). The best solution is to get an aftermarket unit and make the PV's open 500rpm later. Manual adjustment of PV does not work. His last word of advice was that best results are obtained with only a slightly modified engine with well sorted suspension ans tyres (as 'that guy mentioned also).

Jetting is based on throttle position-not revs (if its always at certain revs, then the issue is elsewhere. Put tape round the throttle and label positions (1/8, 1/4, 1/2) then use these to help with jetting. A good tip

Take it or leave it, but I usually take his advice and have only good results

Thanks for that, My biggest issue at the moment is probably more lack of test time on the track. Only time will tell but it would've been nice to have it nearly sorted in time for the weekend

[Billy]

Thanks for that, My biggest issue at the moment is probably more lack of test time on the track. Only time will tell but it would've been nice to have it nearly sorted in time for the weekend

Contact Chris Osborne (Ozzy 27) hes got a dyno set up in Palmy now and is very experienced at 2 stroke tuning.As an example I ran RGVs for a number of years and assuming you bought that bike from Lyttleton it has Sagaya chambers and factory kit spec cylinders with 34mm carbs and a 22d20 control unit which is similar to a set up we tried and we ended up using 320 mains with 55/65 powerjets but we had bored carbs so thats probably only a guide and I wouldnt be suggesting you try that without testing although it does sound like its rich according too your description.Get it too a dyno and jet it properly

[The Pastor]

you can never get 100% smooth throttle with open carbs btw.

a carb balance (a propper one - many crap gauges out there that dont work) goes a long way (mainly for idle, but improvement overall is there)

[phillip]

hi iv got a very similar bike, vj22 double base gasket flowed cylenders sp 1mm head gasket took 0.3mm off the head ( despite what everyone says about fucking with the squish) 32mm carbs and tyga full exhaust system with no top on the airbox

It used to bog down at 8kish, so nana it up to 9k then all hell breaks loose. took it to tripple zee cycles in manurewa and they dyno tuned the carb and abra cadabra no more flat spot and good mid range.

My 2cents worth, get it running good and take it to an expert for the carbs

[7mmWSM]

Bit of confusion with the main jetting sizes so hope some can help.
Some info I've found says for example L = 280 R = 270 and other figures are back to front. I know I need to run one cylinder slightly richer but which one?

As for the test over the weekend... still massive mid range bog so plan b is going back to standard and process of elimination after that.

[SS90]

You run the rear cylinder richer than the front.

It is impossible to say over the "tinternet", but, just for shit's and giggles, let's have a stab at it.

You say "mid range bogging", I can only surmise that in most likely hood it is too rich.

Note-------- One mans "bogging" is another mans "missing", so be warned on that one eh!

One common thing I have seen over the years when people "race tune" their 2 strokes, is they (mistakingly) believe that (after somewhat dubious levels of "porting" (ahem) that they have done "such a good job" that nothing short of biblical levels of fuel (hence bigger jets) are now required..........

More often than not, it is only a 10% increase in main jet is required from standard (RGV250's are quite rich standard anyway).

From your description, I feel there is a good chance that you are simply too rich on your main jets.

Possibly your needle position as well, but only time will tell.

I suggest fitting the original air box (with filter..... don't laugh) and the original carb settings, and go for a test run, see how it feels.

I am of the (experienced) opinion that even with the different expansion chambers, the reintroduction of the OEM airbox and jetting will makes things easier as far as jetting goes.

The likelyhood of running too lean when doing a test run in this set up is very very small.

Then, simply "do one thing at a time"

Remove the air filter, and put the lid back on, go for a short run, and see how it feels/read the plugs, most likely it will NOW be too lean...... increase the main jet my 2 sizes, and test again..............

when everything is ok, repeat the procedure until you can run the engine with the airbox set up you want.

You may well find you have an easier riding bike if you run an air box top, never forget that a two stroke SOUNDS more powerful with no air box, but that is not always the case.

[7mmWSM]

You run the rear cylinder richer than the front.

It is impossible to say over the "tinternet", but, just for shit's and giggles, let's have a stab at it.

You say "mid range bogging", I can only surmise that in most likely hood it is too rich.

Note-------- One mans "bogging" is another mans "missing", so be warned on that one eh!

One common thing I have seen over the years when people "race tune" their 2 strokes, is they (mistakingly) believe that (after somewhat dubious levels of "porting" (ahem) that they have done "such a good job" that nothing short of biblical levels of fuel (hence bigger jets) are now required..........

More often than not, it is only a 10% increase in main jet is required from standard (RGV250's are quite rich standard anyway).

From your description, I feel there is a good chance that you are simply too rich on your main jets.

Possibly your needle position as well, but only time will tell.

I suggest fitting the original air box (with filter..... don't laugh) and the original carb settings, and go for a test run, see how it feels.

I am of the (experienced) opinion that even with the different expansion chambers, the reintroduction of the OEM airbox and jetting will makes things easier as far as jetting goes.

The likelyhood of running too lean when doing a test run in this set up is very very small.

Then, simply "do one thing at a time"

Remove the air filter, and put the lid back on, go for a short run, and see how it feels/read the plugs, most likely it will NOW be too lean...... increase the main jet my 2 sizes, and test again..............

when everything is ok, repeat the procedure until you can run the engine with the airbox set up you want.

You may well find you have an easier riding bike if you run an air box top, never forget that a two stroke SOUNDS more powerful with no air box, but that is not always the case.


Thanks. Thats pretty much my plan.