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Discussion Starter · #1 ·
I took my 1991 MC22 to the track yesterday on it's first outing in my possession. It tops out at 110kph and takes a long time to get there, and I can't get into 5th or 6th gear because it just sits at the same speed.

It seems to rev nicely to about 10k rpm but then hits a wall.

Prior to taking the bike out, here's what I did to it:

New plugs, air filter, oil, oil filter
Carbs professionally cleaned
New carb boots
New fuel tap and vacuum hose
New chain/sprockets
New coolant/water wetter

It was overheating early on but it was also 104degF / 40degC at Chuckwalla Valley Raceway. The reservoir overflowed and emptied water onto the ground after the first couple sessions so I replaced the water each time to make sure it was ready for the next outing. Later on, the temp gauge got up to the M in "TEMP" and stayed there.

After my last session, it stopped making power and slowed down even though I was rolling on the throttle as seen in my video below.

Is this a tuning issue? Something catastrophically wrong in the engine? It has 34,500 km on it.

Here's video from yesterday:

Here's video from a guy in NZ tearing it up, this kind of speed is what I expected. You can see how rev happy his bike is and it shoots to 160kph+ very quickly.
 

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Discussion Starter · #3 ·
I'll check the compression either later this week or when I'm done changing the engine in my Tuono. One project at a time!

The previous owner had the same bike out on the track and it ran great. Is there info on checking the cam timing and valve clearance? I don't know what I'm looking for (and haven't had a chance to look into that yet).

Chuckwalla is a blast on a small bike. Even though I wasn't making power, turning in under everyone was fun! Have you been there before?
 

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I took my 1991 MC22 to the track yesterday on it's first outing in my possession. It tops out at 110kph and takes a long time to get there, and I can't get into 5th or 6th gear because it just sits at the same speed.

It seems to rev nicely to about 10k rpm but then hits a wall.

Prior to taking the bike out, here's what I did to it:

New plugs, air filter, oil, oil filter
Carbs professionally cleaned
New carb boots
New fuel tap and vacuum hose
New chain/sprockets
New coolant/water wetter

It was overheating early on but it was also 104degF / 40degC at Chuckwalla Valley Raceway. The reservoir overflowed and emptied water onto the ground after the first couple sessions so I replaced the water each time to make sure it was ready for the next outing. Later on, the temp gauge got up to the M in "TEMP" and stayed there.

After my last session, it stopped making power and slowed down even though I was rolling on the throttle as seen in my video below.

Is this a tuning issue? Something catastrophically wrong in the engine? It has 34,500 km on it.

Here's video from yesterday:

Here's video from a guy in NZ tearing it up, this kind of speed is what I expected. You can see how rev happy his bike is and it shoots to 160kph+ very quickly.
It sounds like your bike is only running on 3 cylinders. The 2nd video is exactly the way they should sound.
You said you replaced the plugs. Check them again. Check your plug leads.
The problem is likely to be more than just an air leak. Are the plugs wet (fuel on them) after running? Maybe one carb is not feeding fuel to the engine. Blocked float needle value or blocked jet.
It could also be a valve clearance issue as mentioned previously.
 

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Need to look up stock carb-jetting sizes and compare with what you have. Mentioned in other thread that yours were 4-sizes larger than what came in rebuild kit. That would be way too rich and may be causing sluggish response. Yeah, pull plugs to confirm one way or other. Even better to do some datalogging with wideband-O2 or dyno-testing.

When Spears dyno-tuned my Ninja 250, he immediately downsized mains from 98 to 96 even before 1st pull. That's with free-flow intake, airbox snorkel removal and full Tyga exhaust. After dyno run he downsized mains once more to 94 and we got +22% more power than stock! That's 22% more air-flow than stock requiring 2-sizes smaller mains than stock, and it's still pig-rich at 11:1 AFR!

Factory mixtures on Ninja 250 is super-rich, I'm trying to find stock MC19 dyno-chart with AFR...

 

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Do you have factory airbox with fresh filter? Was talking about rebuild kit and filters with these guys: CBR250R MC19 Keihin compatible carburettor repair kit set (4x) CRK002000

They relayed some info about some users in... Thailand I think, who just rebuilt their carbs with kit. They used pod filters with larger mains and bike ran horrible and wouldn't rev to redline. Concurs with experiences with Ninja 250 where everyone who've tried pods immediately reverted back to stock airbox and jetting. Stumbling mid-range and no top-end. Also stutters when encountering cross-winds.

Ninja 250s have been used by millions of racers past 35 years. Racers are cheating lying bastards who will do anything to get an unfair advantage. They only use what works. Fact that they don't use pod filters even though it's allowed by rules confirms that pods don't work.

I recommend putting factory mains back in along with factory airbox & filter.
 

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On my MC22 track bike, I think we got down to 92 size mains in all carbs when testing on the dyno with 42bhp at the wheel. Big jets are the wrong way to go. We also found it best to retain the air cleaner box and the internal baffle. We run a high flow foam filter.
 

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Discussion Starter · #10 ·
Hey guys, I'm finally done with my Tuono and can start back with my CBR.

The airbox is stock and a stock filter. No mods, no pods.

I haven't looked into what jets are supposed to come with it but will do some searching tonight. I assumed the 104 jets that were in there were stock since the previous owner didn't allude to ever changing them and said the bike ran great before they put it in a crate (where it sat for a year). It was just a street bike as far as I know. I also assumed the Chinese rebuild kit just had whatever jets they threw in, and the carb guy said they could throw anything in there. They're either 94 or 96

I do have a spare carb and engine, I should pull those jets out and see what they're marked as and see if they have something different.

So totally stupid question, do I need to make adjustments to the air needles if I change jet sizes? If so, what way do I turn them and how much?
 

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no need to change as they affect different operating zones. Pilot screws/slow jets affect just off-idle and low-throttle operations. Mains affect WOT operations.

Factory config uses 105/102 mains. No one really knows why. Racers will just use same size all across, seems simpler that way.

Did you ever do compression test?

Should also take airbox cover off and look down carb throats. When you rev it up under WOT, does carb-slides open fully?
 

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Discussion Starter · #12 ·
Ok, perhaps I'll try the smaller jets to see what happens. It's easy enough. But first I do still have to check compression and carb function. I just finished my Aprilia and that took longer than anticipated. Now I have some time so maybe later this week.
 

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Thanks for info!

So you went from factory 105/102 mains down to 92 for 20% gain in power? Any other mods besides foam filter?

Happen to have any before & after dyno charts with AFR? I've been searching for those forever!

thx!
Yep smaller jets. More power. Sorry do not have dyno graphs. I wasn't totally interested in the plots, just wanted to get it to run its best for the track. I will chase up my dyno guy to see if he saved them and still has them.
No other mods to the bike other than an aftermarket slip on, straight through muffler.
Peter.
 

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I can not remember, but I might also have changed the needle heights. Not sure whether I went up or down though. Best way to sort out a bike is on the dyno. they all tend to be a little bit different. Just lots of trial and error.
 
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