'89 Moto 4 250 no mid or high-end power... - Yamaha ATV Forum
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post #1 of 3 Old 06-01-2010, 06:52 AM Thread Starter
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blah '89 Moto 4 250 no mid or high-end power...

Ok, so I finally got he moto 4 running about two weeks ago.. turned out it needed a valve job BAD... so, I got the thing running, new spark plug, carb is spotless... I had to hijack a piece of exhuast off of an old dirt bike (4-stroke) to use on my quad since it didn't have the header pipe when I bought it... The pipe I put on doesn't seal real good, now for my question... the bike seems to run ok on flat ground, but as soon as I start up any grade, it just loses all power. most times i have to put it in low-2 to get up slight hills... also it will not rev up past half throttle even if sitting in neutral. Could this be caused by the exhaust or do I have some other issue going on here??

Oh yeah, also I have tested compression and it's running at 153psi and the timing is dead on... Any help or suggestions will be greatly appreciated.
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post #2 of 3 Old 06-07-2010, 03:35 PM
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Sounds like a needle and seat issue. That would be the first suspect when changes in grade affect performance. Turn the gas off and pull the fuel line, pull the bowl off and see how full it is. It should be 2/3 or less.. If it is too full of fuel the carb bowl does not vent properly and can suck up extra fuel. If the bowl is nearly empty you will have to adjust the float to keep more gas in the bowl.. If you have never changed the needle and seat it is an inexpensive preventative maintenance issue if you have the carb off anyway.

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post #3 of 3 Old 06-07-2010, 05:49 PM
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I'd start by sealing that exhaust!!!! backpreassure is critical on a 4-stroke. Then work on the carb tuning.
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