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xr80 stumble/cutout problem

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My son's 01 xr80 has a bad stumble off idle and is very weak when climbing hills also seams to cut out about half way through the rpm range. building hotrods for years i figured that the carb. was the problem. I disassembled it and cleaned every passage in it with compressed air/ moved the needle up two notches/put float level in proper position. to my supprise there was no change in performance at all. I've been all over the idle mixture screw with very little change? Does any one have any ideas??? would the timming be a little retarded? It starts easy 1/2 kicks with no choke!! I,ve Checked valve adjustment,Cleaned air filter,Run racing fuel through it,checked to see if it is getting fuel properly, but no luck!! any help would be greatly thanked

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You need to clean the carb again with YAMAHA carb cleaner. Leave the chem dip in the jar. Trust me. Fully disassemble and soak overnight and 1/3 gas vs. 2/3 carb cleaner. Blow out with air and inspect each jet. Run each part under water before assembaly. Set all adjustments back to factory. Every xr 80/100 has a horrible stumble off idle with any thing over 1/2 throttle. Just the way it is. But cutting out on a uphill is very strange and at that point is only drawing off the main and needle jet. Either way clean it with YAMAHA cleaner I cant stress this enough as it truly is the best cleaner out there.Clean it first then report back.

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Hmmmmm. . . How was it before or was it always like this? Did you pull the pilot out and then blow through it? Air leak maybe?

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Well, I've rebuilt several holley and quadrajet carbs over the years and you are wright, soaking the carb over night gives the carb dip a chance to clean and loosen debrie , thats what i did on this little bugger!! what if i drill the pilot jet to the next wire size dill bit?? It's a .035 now ,I could make it a .040/.042. On a CAR A STUMBLE means it's not getting enough fuel when the butterflies are suddenly opened.It acts lick it's running out of fuel at mid range and then catches back up! I'm stumped but i did take the spark arrestor out and it ran alot better!!But still stumbled!

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I took all jets out disassembled the hole thing Soaked it and blew through every hole, washed in warm water and blew again!! It's was running like this when I bough it from the bike shop!!

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Not being an arse but was it Yamaha carb cleaner. Believe me car cleaner doesnt do the trick. Please please do not drill a jet. As far as timing goes it sounds like its to advanced and detonation is occuring in turn killing full load power but low power is strong. Just hit it with a timer,.

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You most likely need to replace the needle jet and the needle you can get these part from Honda in a kit, what happens is when your throttle is slightly opened the fat part of the needle which is just slightly smaller than the hole in the needle jet will rub together and finely get worn enough to cause that off idle stumble that makes your bike a lot less fun to ride. The needle gets worn and the hole in the needle jet gets worn out of round most of the time not Evan enough to see but enough to make you not want to ride the thing.

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I have the same off idle stumble with a 05 CRF 80. I bought a larger pilot jet and main. I will let you know if that helps. I think its jetting.

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Have you checked the gas tank? Sometimes the petcock filter can be stuck with debris. Put clear gas lines on so you can see if she is getting gas to the carb. JK

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good job did the same to my 100 except fmf pipe runs greaaaaaaaat now I love lots more fun to ride

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