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TTR 250 after firing/ red hot header

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Hello everyone, I just bought a 1999 ttr 250. I got a good deal on it, and now I’m doing some small jobs and maintenance to it. During my first ride I noticed that it sounds like there is an exhaust leak where the header meets the head, but only at higher rpm and under load. <50% rpm I don’t hear it at all. I’ve also noticed when pushing the bike hard the header glows red hot. And under engine breaking I hear a muffled backfire sound from the header area. I have adjusted what I believe is the air/fuel screw on the carb (star shaped screw turn by hand) to a very rich setting so the bike bogs, then lean it out just enough so that it doesn’t bog. With that being said I don’t think it’s running too lean. I used a new header gasket as well.

 

I checked the valve clearances and both intakes are pretty much in the middle of the range provided, if I remember correctly they were 0.13mm and 0.14mm. The exhaust valves however were both tight. Between .14mm and .16mm. The acceptable range is below. 

Intake 0.09mm ~ 0.19mm
Exhaust 0.19 ~ 0.27mm

I have never adjusted valves on a bike that uses a shim system before so I had to order the shim kit. The kit just arrived and I’m going to get those exhaust valves in spec. 

 

So I guess my question is: Do these symptoms sound like the result of tight exhaust valves? Anything I should check that would relate to the problem? 

 

Thank you in advance.

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I'd definitely get your valves in spec but I don't think your exhaust valves are causing your symptoms -I think you are lean. What clip position is your main needle on? Might try dropping the needle one position depending on where it is. What does your spark plug look like? What is the condition of the carb?

My 225 header glowed at idle when I was excessively lean.

 

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Ok, update: 

I just adjusted the exhaust valves and brought them in spec. I noticed both sides of the carb were semi disconnected from the engine/air box. I connected everything back up the way it should be and between that and the valve adjustments, I think I solved my hot header problem. Took the bike for a quick spin (in the dark) and I didn’t see any signs of red. 

 

Im still hearing a muffled backfire noise on deceleration, it sounds like it’s coming from where the header meets the head. I have removed and installed the exhaust a few times now and used a few different header gaskets. I don’t see any cracks anywhere or anything like that. 

 

The bike runs/idles/pulls great and now with no glowing header I’m going to leave it as is. I can barely even hear it with a helmet on. I might just be critical comparing this 20 year old ttr to my brand new Crf which is pretty much silent. 

 

Thank you for your input. 

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13 hours ago, Drw814 said:

Ok, update: 

... I noticed both sides of the carb were semi disconnected from the engine/air box. I connected everything back up the way it should be and between that and the valve adjustments, I think I solved my hot header problem. Took the bike for a quick spin (in the dark) and I didn’t see any signs of red....

Added air due to a leak can cause an excessively lean condition = running hot. Good job.

 

 

Thank you for your input. 

 

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