Hi could anybody give me an idea of what might be happening to cause the rear cylinder to run extremely week above 10,000rpm.
Just had the bike on the dyno and the front/right cylinder was running ok through the rev range apart from some tweeking to get it spot on but when testing the rear/left it would be ok to about 9000rpm and the suddenly just go off the scale running lean.
Now i know it is a very vague question but any hint would be useful. My first job is to check the float heights and for any debris or blockages but is there anything else likely to cause this? Jetting wise the rear is 2 sizes bigger on the main jet and the power jets are still fitted.
Cheers
Mark
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MC21 300
Aprilia RS250 track bike

Have you had the power jets out and cleaned the passage ways to it?

Most NSR's (apart from moded crank cases ones and 300's) tend to run bigger main jets on the lower cylinder.

Apart from running lean whats it looking like?
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If I have to take the carbs off once more...

stephen
Unfortunately i could not check the power jets last time the carbs were apart as the heads on the alloy screws are knackered, may need to drill them out and replace if there still available. Should i run power jets as large as possible?

Power was very low for a 300 kit [can't say as the abuse would be too great from all 300 haters!!!] but then it only did one run when we found this problem.
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MC21 300
Aprilia RS250 track bike

You can't buy the power jet screws. You have to get a really good fitting screw driver, give the screw a smack and it should undo with a bit of a crack.

I used to run mine with the biggest power jets I could get (think its #80 or is it #75 I can't remember).

To quote Fontyyy, run jets that could power a space shuttle.
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If I have to take the carbs off once more...

Just been reading the tuning section again with respect to the HRC jet kit and it mentions that the Red + should have the one side going to fresh air. I noticed on mine it is plumbed back up to the air box via the standard pipe work. So will this be causing me problems?
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MC21 300
Aprilia RS250 track bike

Not really, it just means your set up will differ from HRC's base settings. The bike will still perform alright. Its only vented to air when you arnt running an air box.
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If I have to take the carbs off once more...

Hi Mark,
talk to Stephen, he really does know this set of barrels.
I took his advice when I ran them, even with my dodgy jetting, they still went like stink.
When I eventually got used to them, even with the crappy jetting, the thing was pulling wheelies away from the lights & power wheelies in second in the p!ssing rain. Was lifting the front in third too.
Was super safe, if a little rough through the rev range,the way I had it.
I know you`ve had it tuned by a reputable tuner. It`s just, I would think Stephen Probably knows NSR motors a little more than him.
You could do a lot worse than giving Steve a p.m.
Cheers,
Roy.

Hi, i am back again after another failed session on the dyno. Still getting the same issue of the bike running lean but also not wanting to rev either. This is with another set of carbs and a new airbox!!!!!!!
I have removed the intake rubbers and checked the gasket and reeds with no obvious problems showing so refitted. Also removed the exhaust on the one side where there was a slight oil/fuel weep on the barrel and ensured no signs of problems inside the barrel and refitted with a small amount of sealent on the exhaust flange.
So i am at a loss now, is there any way electrics could cause this problem. The bike has an HRC delimiter but i cannot imagine this would fail but unable to remove from the loom as i cannot wire back into the PGM. It has two grey plugs connecting into the loom [from the delimiter] and not the single black connector which fitts on the PGM.

Is there a difference between the black + piece for the air solenoids and the red item supplied with the jet kit?

Any other advise greatly appreciated before i loose heart.
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MC21 300
Aprilia RS250 track bike

The red and black X's are different. They have a different size air jet installed. Shouldn't make much difference to having it set up though.
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If I have to take the carbs off once more...

I think I still have the black plug. I think you could use it by fitting the OEM spec bullet connectors I used.
From memory I`m pretty sure I fitted #75 power jets in both carbs on the original set.
On my race bike, I`ve just gone the HRC route & fitted blanks to the power jets. Filled them with solder as per the advice in the tuning section. Perhaps you could try this & eliminate the power jets altogether?
I wonder if the TPS on the new set of carbs may be causing the new -not wanting to rev issue?

Hi Roy, yes think i need to swap over the tps from the one set of carbs just to eliminate this as well. PJ are still #75.
If you still have the original plug that would be great i can try removing the HRC bit just to see if it will run any better.
Cheers
Mark
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MC21 300
Aprilia RS250 track bike

If it's going lean on only one cylinder, then it won't be anything to do with the T.P.S.

Maybe the left crank seal drawing some air, a warped/cracked/leaking inlet manifold/rubber, or weak jetting/needle in the left carb.

The stock and HRC X and Y pieces effect BOTH cylinders equally. The power jets are independent of one another, and will make the jetting progressively richer as the RPM (and therefore airflow through the carbs) increases. This is what can make setting with them tricky, and why HRC eliminate them. The bonus of using the power jets is that you can use smaller mains which makes low to mid-range throttle more responsive.

Remember, the HRC X and Y are for use with NO airbox and NO power jets. As with pretty much any HRC part, it's unlikely to work unless you use ALL of the kit!

Try going down on power jet size on the right cylinder and upping the mains in both carbs. A stagger on the jetting is common, and even if you run two mains that are the same size, you are still staggering the jetting by using two different PWJ's.
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Andy.
NSR-WORLD.COM

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Andy
Cheers for the info, so overall is it best to stick wirth PJ's and the standard + and Y pieces if running airbox or go for blanking the PJ's, running airbox modded with HRC + and Y?
Will try the jetting suggested next weekend if i can get a smaller PJ by then and do a quick run on the road rather than drive 1 hour to the Dyno. If that does not work then i suppose its an engine out to check the left crank seal.
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MC21 300
Aprilia RS250 track bike

I don't think Matt has had any issues running a 300 with the stock setup before. Not only is the red X-piece different to stock, but the Y-piece is too, so it can all effect the end results, and those parts were not only designed not to be used with a restrictive airbox or power jets, but also to be used for a 250. I'd personally eliminate them from the equation.

The integrity of the seals and inlet manifold can be checked with the motor in place. The most crude way to check the left seal is with carb cleaner and the motor running. If it's sucking in air there and you spray carb cleaner behind the flywheel it will soon tell you if you have a leak.

If there is a leak, but it is more subtle, then you will need a leakdown tester. It can still all be checked without removing the motor though; even the crank seals can be replaced with it still en situ.
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

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Originally, it ran okay when I had it with the kit "X" & "Y" pieces used with the airbox in place & standard plumbing. I`d drilled loads of holes in the airbox lid and the centre dividing section inside the clean bit.
I only ever ran with it jetted very rich. So it would hit a flat spot in the mid range. Revved out okay though.
I thought it would have just needed tweaking a bit on the needles & dropping the mains slightly then.
When it seized when you were playing with the jetting, which cylinder went Mark?