old xr600 q's

I have an older ('88) xr600r. It runs great low and mid range, and flattens out at higher rpm. I have a stock exhaust. Any suggestions on getting a better performance out of the top end? What type of exhaust do you suggest? Will repacking the stock exhaust help? Bigger main jet size?

I have an older ('88) xr600r. It runs great low and mid range, and flattens out at higher rpm. I have a stock exhaust. Any suggestions on getting a better performance out of the top end? What type of exhaust do you suggest? Will repacking the stock exhaust help? Bigger main jet size?

we'd kinda have to know your jetting specs and elevation in order to suggest a jetting change.

also, are your valves in spec? is your air filter clean? is your spark plug tired? try the simple and cheap stuff first.

I'll have to look and see what the jet size is now. I am not familiar with the history of the bike. I live at about 5300 ft and ride from there to 10000.

The spark plug is new. An NGK that was recommended by the manual. As far as the valves go, they should be pretty good. When I first got the bike a few weeks ago, I adjusted the valve clearances, and they don't make a racket any more. I also run 91 octane gas, and just cleaned out the air filter. Do you run at elevation? How about your exhaust, is it stock? If not what differences did you notice?

My 1985 xr600r has a similar problem. The power on mine would plateau at a little above midrange. I went through and ran many tests with the air system and the fuel system. None of these things helped but what I figured out is the timing would not advance when I revved the rpm's. I ran tests on my CDI and found that it was fried. So check your CDI and run the tests in a manual to check the ohms of the CDI.

The stock XR6 isnt exactly a sizzling top-end bike. But if your bike is dying or spluttering with a twist of the throttle, attention is obviously needed ie clean carby/airfilter and recheck valve clearances. To get a top-end horsepower gain you'll have to spend some $$. To get a small gain replace the stock exhaust and header with one of the better aftermarket systems, then you would go for a free-er breathing airfilter and rejet the carby if required.

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