Question about 1982 Yamaha Xj750 Xj 750 Y140 Maxim Air Box

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I hve a yamaha xj750 1981, cleaned carbs, bigger jets(122) because of exhaust, starts very weel, pullaway good when cold, as soon as heatd up it stutters under 3000 revs, above 3000 it goes well but t

Yamaha xj750 1981

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Check to make sure that you have no intake or exhaust leaks anywhere in your system. Once you have made sure the system is sealed you need to perform a plug chop and read your spark plugs to find out if you are running rich or lean in that particular throttle position and adjust the carburetor accordingly. Judging from the ramp range you stated, it sounds like your jet needle may be running rich. If the needle has different clip positions you may want to move the clip up (so the the needle sinks lower into the carb) to lean it out a bit on that circuit. You may also have to adjust the pilot screw as depending on the throttle position it may also be affecting this rev range. Another possibility is that you may have gone with a main jet that is too large. You stated that the new main jet is a 122 to compensate for an aftermarket exhaust. What was the original main jet size? Usually exhaust changes do not need much if any jetting changes. One to two sizes up is all you would need at the most.

Posted on Jan 26, 2013

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