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Racing Ruben

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Hey everyone,

Went for a quick drive today. Noticed I couldn't get to high revs. So I cleaned the carb. When I was revving the engine to check if it still stuttered, this is what I saw: a blue flame coming from the exhaust when I released the throttle.
I hope this doesn't hurt my bike cause I kind of like it ;D

Ruben
 

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Think you have a rich mixture there son..
May also be faulty intake/exhaust resonance causing unburnt fuel to ignite in the pipes. Are you running completely open exhausts? May require some kind of baffle for backpressure.
 
The exhaust does have a baffle, but the mixture might be too rich indeed. My jets are 48/95 and the air/fuel mixture on the carb is set 1 and3/4 turns open.
The connection between header and muffler isn't air tight. Could that be the cause?
 
Racing Ruben said:
The exhaust does have a baffle, but the mixture might be too rich indeed. My jets are 48/95 and the air/fuel mixture on the carb is set 1 and3/4 turns open.
The connection between header and muffler isn't air tight. Could that be the cause?

Well, it certainly won't help. If you have an overly rich mixture, fuel leftover from the combustion chamber will go to the exhaust. The vacuum created between pulses in the exhaust will suck air into the exhaust through the gap, now you're mixing the excess fuel again with oxygen, and given that the exhaust runs very hot... combustion is bound to happen ;)

what are the mods to your bike? if you have the stock airbox, with stock carburettor, then 48/95 jets are too rich. I am currently running a K&N high performance filter, stock carbie with choke butterfly removed, and an ooracing header with reverse megaphone and 2 baffles. I briefly ran 48/95 jetting before upping to 50/100, and I haven't had any fuel igniting in the pipes.

Take into consideration that I live in Madrid, which has an elevation of 650 meters over sea level, so it is running a tad rich, but I still have not had a single incident of fuel igniting in the exhaust.

You, as I can see, live in antwerp, which is barely 3 meters over sea level, so there is defiinitely something wrong with your setting.
Work your way checking step by step:

1- Seal off the connection between exhaust and header. Use exhaust paste, or a metal adapter or a combination that suits you.

2- If combustion still occurs, lower your jetting to adjust to the airbox (if you have it). check this forum threads to find what are the stock jetting of the Ace, then go just a little higher to compensate for running a derestricted exhaust.

3- If none of the above work, maybe the muffler design and construction is creating hot spots against which the unburnt fuel ignites. But then again, if you adjust jetting so that no fuel is left unburned, you can't phisycally have combustion, no matter how much air leaks into the exhaust. :p
 
I also have the ooracing header, removed the standard airbox and replaced with power filter. I removed the choke cable so the butterfly valve is wide open all the time. The muffler is a trumpet with a whisper baffle for back pressure
Thanks for the advice. I'll fix the air leak and change jets. That will probably fix the problem.

By the way: I love the pics you posted
 
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