popping on stock 06 yz450f exhaust

Also has never uni air filter, fresh oil n filter, replaced antifreeze with engine ice..akrapovic full exhaust

Sorry meant "NEW" uni filter

Also new plug. .old one looked like a fouled 2-stroke plug wet n dark??

@crpilot315 Did you ever find a solution to these problems?  I'm having many of the same problems with an '08 that I bought.  I've been wrenching on bikes ever since I was a kid, but I hadn't owned a YZ450F until now, so I'm still trying to learn how it differs from my others.


It started with just being extremely difficult to start (100+ kicks) and once I got it idling, it would die as soon as I pushed the choke in or even touched the throttle.  Those are normally symptoms of a gummed up pilot jet, so I pulled it and cleaned it, put it back in, and now it starts first kick every time with the choke on, and I can push the choke in and still keep it running.


HOWEVER... now I'm getting a ridiculous amount of backfiring, the throttle bogs and hangs for an eternity before it responds, but the most alarming problem is that the radiator is boiling over extremely rapidly, within 30-60 seconds (just as you mentioned).  Granted, the bike wasn't moving, so there was no airflow through the rads, but I've never seen a cold radiator heat up and boil over that quickly.  And its not like I had it pinned either, I was just rolling it on easy from idle to mid-throttle.


Off the top of my head I can't think of what could be causing that specific set of issues.  If it was just excessive backfiring and boggy throttle response, I would normally assume there's some jetting problems... but the radiator boiling over is strange.

@nuclear_ cowboy...I gave in and its at the Yamaha shop..there starting by completely rebuilding carburetor the mechanic thinks its a worn needle but still doesn't make sense to me either why it would boil over within 30 seconds I'll keep you posted!!

Edited by crpilot315

Nuclear_Cowboy update!! Well the mechanic found the problem and this hole time it was just the o-ring that was bad on the quick adjust for the air/fuel screw!!! Runs fine no bog no smoke no overheating!!!!!!!!!

Never thought a little o-ring could cause so much havoc, disorder, frustration and anger!!!!

Glad to hear your problems are solved... I can't comprehend how or why that little o-ring on the fuel/air screw would have caused those issues, but that's good to keep in mind in the future.  


I'll tell you what I did, I  ended up pulling the carb again and instead of trying to clean it I just replaced the jets with new ones.  For some reason that seems to have fixed all of the problems, so maybe the problem was I just didn't do a good job of cleaning it the first time.  But I was convinced that there were more problems than just with the carburetor, considering the radiator started boiling so quickly.  Yet, after changing the jets, there was no boiling anymore.... so just as an experiment I leaned out the mix to the point that I had to keep it mid throttle to keep it running, and sure enough the radiator started boiling over within a minute.  


As it turned out, it was just the carburetor all along.  Apparently a super lean fuel mixture can make your engine run hot enough to boil the radiators.  I did not know that until now.  I knew lean = hot, but I didn't think it was THAT extreme.

Glad to hear yours is running right now too Nuclear _Cowboy!! Ya I never new a lean condition could cause it to boil over either!! Just rode it today just some trails it still popps but I tuned it out but that dreaded bog is gone now and it absolutely rips out of tight corners now!!

Edited by crpilot315

Pends on your elevation, too. I'm at 700 ft and mine took a 50 pilot jet. Yamaha mechanics at the local shop say Yamaha recommends 48 for my area. I know of others resorting to the 50 as well. Higher elevations, where the air is thinner, will probably require a leaner pilot jet than the 48-50 for my area. Check with your local Yamaha mechanic.

In Texas also, put a 50 pilot jet in and no more excessive popping on decel. There also is not any noticeable bog anymore... 

Do you have the o`ring `s sizes?

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