YX150 backfireing issues

[snicko54]

I have a yx 150cc had it for about 8 months hasn't ran right since after the fist 3 months after I got it it has a pissy 22mm carb stock it started fine and was alright at idle but as the revs got up it started to back fire and pop and the throttle respoce wasn't there and was bogging out ive checked for all air leaks exhaust it tight cant figure out what the problem is im buying a oko soon as I have enough coin just wanting to see what u guy's thought it could be a mate suggested the valve clearence could be out but im no mechanic it has totally got me stumped any info or advise would be of agreat help

 

[motodevo]

22mm is tiny for a 150, backfiring could be from carb being to lean, was the carb off a smaller motor?

 

[snicko54]

nah mate come std with 22mm mikuni its a braaap classic bling yx150cc its the only problem ive had with the bike

 

[my67xr]

yeah, i'd be checking the valves if you haven't before.
.003" on the intake, .004" on the exhaust
http://www.youtube.com/watch?v=QJciyJRJh8Q

 

[8r3nd0]

You say exhaust is tight, is there actually a gasket in there as my motovert when I got it basically new didn't have one and it was tight but still had a leak also just double check your carb and jets are spotless.


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[snicko54]

ill be buying a oko soon but will be getting the valves looked at I was hoping to fix the prob myself but I couldn't figure out why it was going on

 

[my67xr]

i'm guessing the 22mm carby you have is the china copy Mikuni 26/22mm ?
they go pretty good once they have been rejetted/adjusted

there are a few threads here on tuning them etc

pm replied to also.

cheers, craig

 

[my67xr]

another thing with the backfiring,

it may be a dodgy connection in the wiring for the coil, cdi, spark plug cap, or even a faulty spark plug too.

and check that the slip joint, from the pipe to the muffler is tight as well.
loosen the muffler clamp, wiggle them apart, smear some silicon etc on, push 'em back together and do it up again

 

[snicko54]

I told braaap it maybe elec so they sent me out a new spark plug and cdi and it still did it and I also brought another carb that was the same and still stuck with same problem I live 3 hours away from braaap and never go to the city my bike has the lifetime warranty but they havnt seemd to help me much on my engine problem

 

[zwebx]

my engine always backfires coming down rpm, not like a loud bang but a pop almost every time i come down it just because of my cam grind i think, sounds hot

 

[my67xr]

have you jetted your carby to suit the bike ?
the china Mikuni's seem to like bigger pilot jets, a #20 or even a #22.5 might help it out a bit.

 

[8r3nd0]

have you jetted your carby to suit the bike ?
the china Mikuni's seem to like bigger pilot jets, a #20 or even a #22.5 might help it out a bit.

Craig's right check the pilot jet, and if its not a 20 or bigger then try re jetting.
I was running on of these carbs on my 88 engine and it didn't miss a beat when dialed in mate and even with that little engine I had a 20 pilot in it.


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[snicko54]

was funny cos I brought a bigger 26mm carb off a mate for $20 it was off a motovert 140 expert and I started my bike but the revs were low and it stalled and I havnt been able to get it started since then but for the few seconds it ran it sounded way better and felf stronger I did a full rev with out backfireing and it stalled got me stuffed I spent 4 days straight trying to start it but still no luck

 

[Phil67]

Ok I have the same bike, same carby, i'm running a 107.5 main jet which improved the bike out of sight, You are getting backfiring from an exhaust leak at the header or your valve clearances are out. If they have never been adjusted since new, then they are out for sure. Tighten the header nuts a tad, check valve clearances, put clean fuel in the bike and test. My bike does pop on decelleration a bit, normally thats an exhuast leak, but ive replaced that damn copper gasket 55 times, so it aint that.

Where do you live? Pm me your details and I will sort it out for you with Braaap.

 

[Phil67]

One more thing, have you ever cleaned your air filter? Bet ya you have dirt in the fuel bowl