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ThrakenH04

Valves

13 posts in this topic

Ok well I was riding today, not really getting on the gas much but alot of wheeleing action in all gears then after just crusing I get off the gas in 4th and it suddently starts poping and backfiring like crazy, I mean really loud and poppy sounding. my question is, is it time to reshim the valves? seems like to me that the intake doesnt have enough clearence. God I wish everyone had the same valve designe as KTM does. By the way, I need a quik answer because I would like it if I could it to the track on the weekend.

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If it did this all of a sudden, and it doesn't seem to run any different, what it's time for is to relax, chill, and look for the air leak in your exhaust. Start with the midpipe clamp if you have one, and then check the head/header joint. Really.

If that doesn't pan out, try just backing the idle mixture screw out a 1/4 turn or two. If that fixes it, and it was a sudden occurrence, it could have a bit of dirt in the pilot jet.

One thing else, if it's a YZ450, is that the plastic nut that anchors the hot start cable in the carb may have broken and let the hot start air valve come off its seat, which would make it very lean.

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The YZF valves have spectacular durability. Pop the cover off and check the clearances, it's easy to do. If it started suddenly I vote more for something carburetion related; maybe a chunk of goo in the pilot jet, maybe the hot start is stuck slightly open, etc.. Did the climate suddenly change, or did you change anything else on the bike (remove a quiet insert from the exhaust , etc..)?

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The YZF valves have spectacular durability. Pop the cover off and check the clearances, it's easy to do. If it started suddenly I vote more for something carburetion related; maybe a chunk of goo in the pilot jet, maybe the hot start is stuck slightly open, etc.. Did the climate suddenly change, or did you change anything else on the bike (remove a quiet insert from the exhaust , etc..)?

I run the JD jet kit with the full White Brothers Aluminum RACE E-Series, and the Zipty fuel screw. I dont see how I could suddently get an air leak but I'll dissasemble and look for it. the climate never differs around here and if it does, its around 1-3 degrees in difference. I hope it isent the valves because that means they are wearing pre-maturly. I've already re-shimed and that was about 3 months ago.

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When your valves get out of adjustment what kind of changes do you see in your bike???

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Same thing happened to me and it turned out to be a pluged pilot jet. Pull off your carb or pull the bowl apart and pull out the pilot. I bet a twelver it's plugged. Mine had a tiny piece of cloth stuck in it, no idea how it got there.

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A little Water in the gas? Pull tha carb and clean it and test.

Air filter tight?

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out of gas ?? pilot jet blocked ?? I doubt it's valve trouble, sounds like you've been reading the honda forums and are valve paranoid. i have 150 hrs on my 450 and valves are still in spec, haven't moved at all. :)

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Ok everyone well you were right, it was a clogged pilot. alittle piece of a metal shaving. probably from when I was drilling out some rivits in my old 125s clutch basket. 100hrs of riding time and the valves are still in spec.

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