03 yz450.. Whats going on!!!

Ok, im sitting at home, and im about to go to work... Got a phone call from my uncle, He says, that the pipe is getting ULTRA red.. pretty far up on the pipe, I told him that ive read it is normal for 4strokes to get hot like that while sitting and running.. And its backfiring.. he says through the carb and pipe? A friend of his who works on bikes came over and said that its a timing problem that the valves are staying open for too long.. I know nothing about it so i dont know...

Also while messing with the carb and stuff and new spark plug, the fuel cross over hose touched the pipe the other day scared the crap out of us.. so he put a hose he had that was the same size but for a car just temporaraly on there while he looked at the bike.. and during the phone call he said the pipe got hot enough to melt it without even touching it.. Ive done searches just not coming up with much...

He claims the pipe looks hot enough that you could push somthing through it.

It's running a little lean.A just your fuel screw out at 1/4 turns until it runs smooth and no popping.It is normal for the header to glow red if it idles more than a minute or two.

Ok, He says they adjusted the screw, and it never stopped backfiring.

Check your exhaust where it bolts to the head to ensure it is tight and also make sure it's tight where the header meets the muffler. Check the boots before and after your carb. It sounds like an air leak making it run lean.

Then your valves are probly tight.Pull the valve cover and take reading and adjust if needed.

And make sure the timing is correct while you have the valve cover off!

The red exhaust is normal if the bike is allowed to idle longer than 30-45 seconds. It has to do with the retarded ignition timing at idle, and the aggressive cam timing.

Backfire from the exhaust on decel is also normal if it's moderate. If it's excessive, you may have the hot start plunger stuck open, an air leak in the exhaust, or the pilot circuit is adjusted too lean.

Thanks for your time, all of you... Ive done Forum searches, and googled this but i cant find anything on Backfiring through the carburetor, has anyone ever heard of this? I told him ive not found anyone with that problem.. but he insists' it is doing so..

Anyone ever heard of a yz backfiring through the carb?

Yes, and it's usually either a tight valve or an ignition problem.

It's hard enough troubleshooting stuff long distance as it is, but now you are asking us to evaluate info that you're getting second hand. Oy.

Disconect the Throttle position sensor on the carb and see how if it improves. If not the hot plunger is stuck.

my 03 header doesnt seem to glow red hot when idleing for a minute or so. maybe it seems longer than it is cause i dont got a stand so im not waiting around lol

...Mine takes about 45 seconds.

my 03 header doesnt seem to glow red hot when idleing for a minute or so. maybe it seems longer than it is cause i dont got a stand so im not waiting around lol

Try it at twilight or darker.

Yes, and it's usually either a tight valve or an ignition problem.

It's hard enough troubleshooting stuff long distance as it is, but now you are asking us to evaluate info that you're getting second hand. Oy.

Sorry Grayracer, I was just wondering about carb problems because i couldnt find any info on carb backfire. But turns out to have been tight valves :) The guy also did some stuff to the carb.. they said the bike is running amazingly strong, better than when i first got it last May. He said the pipe isnt getting as hot at idle, and backfire is gone except a very small amount every so often at decel... thanks so much guy, ill keep you update.. TT is the best forum i think ive ever been on, on any subject, people really know their stuff and care about bikes. thanks again.

Find out how much change in shim size the valves needed.

The hot start plunger threads on the nut (into the carb) are made out of plastic and easy to strip. It's an easy check to verify if it's popped out of place.

Find out how much change in shim size the valves needed.

My uncle said 3mm?

Seems like alot to me.. But i didnt see it. and they say its running terrific.

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