Back firing into carb i think

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crazypete00

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Hey guys. me again with ore problems. so my yfm350 warrior has been sitting for about 2 years. after a new battery and a few new elec parts it is finally running. however i have a strange idle issue.

it wont idle properly. sounds like it backfires into the carb and splutters.

if i hold on the throttle a small amount it does it less, and from half throttle onwards its fine no backfire. it idles fine with the choke on and if i screw the idle screw further in, but a obviously its higher rpm and dont want it to idle that high.

i took the carb apart today and cleaned the main and pilot jets, both were fine. they are still the stock jets 145 and 42.5. the quad is fairly standard just running a fmf exhaust.

here's a video of it doing it. https://youtu.be/PnPGATxSGjY
 
You need to rejet to run that exhaust. Your running lean. that's why you are back firing from the carb. Got to go up in size on the jets
 
ok thanks, i checked the timing which was fine. i also checked vavle clearance and both inlet and exhaust were too tight. so i have adjusted them.

i have a few new jets turning up this week and a carb rebuild kit so hopefully that will sort it.

I dont think its the jets as i have owned the quad for 12-13 years and it ran fine for the first 6~ years and nothing has changed in that time. While i'm on the case of sorting the issues i will probably mod the airbox and get a decent filter so jet sizing may change.
 
Turn your air fuel mixture screw out a few turns to counterclockwise this will richen it up. The air fuel screw is bottom of the carb by intake boot


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Warrior won't start

okay peps got a questions, got the rebuild back together, and she's getting gas and timing is aligned and valves are clear, and she has spark, but no start, and have a recommendation or ideas of what's going on?
 
I bought mine not running and it had the same issue. Turned out someone adjusted the valves with the piston in the down position but cam mark aligned.

I made sure the piston was TDC and cam aligned on the mark, adjusted the valves and it started right up. Remember the camshaft turns half the speed of the crank. One turn of the crank is half a turn on the camshaft.
 
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