Kymco Mongoose 90 running very rich - ATVConnection.com ATV Enthusiast Community



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Old 06-13-2018, 09:30 AM
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Default Kymco Mongoose 90 running very rich

Guys, I have a 90cc Kymco with the auto choke. The ATV started running very rich on the mid to high end. It is a stock ATV with no performance stuff at all. so far i have cleaned the carb very well several times. Replaced the auto choke assy. Plugged the two holes that the auto choke feeds with RTV to be sure it is not flowing gas. Lowered the float , set the needle to max lean ( clip at top). This seemed to help some.I removed the air filter, replaced the plug, compression is 121 psi. It is still running very rich and bogging out. I cannot think of anything else to try. It starts and idles perfect and runs great up to maybe 30 percent throttle then starts leveling off and will just bog as you try to continue to give gas.
Anyone have any ideas?
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Old 06-13-2018, 12:03 PM
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2 or 4 stroke?
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Old 06-13-2018, 02:30 PM
Weekend Warrior
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4 stroke
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Old 06-16-2018, 07:51 AM
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Sorry.. not a big 4 stroke fella but when others reply, they usually start with valve adjustment.
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  #5  
Old Yesterday, 02:45 AM
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Running rich is one of three things, too little air, i,e, air filter clogged, or too much fuel, choke stuck open, wrong main jet or carb assembled wrongly, or a high speed misfire due to an electrical problem. You have eliminated most of these, so probably either an incorrect assembly of carb or the high speed electrical problem. This is one of the few occasions I would recommend a replacement carb. For most Chinese engines they are very cheap and, although the bike may not run spot on without tuning, it probably won't run excessively rich unless the fault lies in the ignition system.
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Old Yesterday, 10:58 AM
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Kymco is Tiawanese. No crappy china here.
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  #7  
Old Today, 09:42 AM
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Thanks guys, One of by buddies has two identical Mongoose 90s. we swapped the CDI and the ATV runs exactly the same. I let the boy ride it around for about 30 mins and it seems to run great as long as he stays 1/2 throttle or more which is where he usually is. When i jump on and run it up to about 3/4 it starts bogging about where the main jet would come into play. It cannot be the wrong jet because its never been changed and cannot be air because the air box is removed. Its not the CDI because mine and buddys work the same. Could it be the coil that runs to the plug? Like merryman said above, maybe its time to swap carbs and see if it improves. I think my honda CRF70 has the same size carb as well so i could swap that. Ill post my results whenever i try something else.
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