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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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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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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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