Yamaha 06 yz450 issues / questions

[Mr. C]

So my son(Little Mr.C) is trying to get this running for his BIL.
Carb has been completely cleaned and torn apart, fuel tank cleaned and fresh gas, new spark plug.
He’s getting a rpm change from a idle to when he runs it a few blocks to a high idle.
Idles fine. Rev it or ride it and the idle stays really high. Also it has a lug ( kinda like a loaded outboard until it clears out.) in first gear doesn’t happen into 2nd.
Could it still be carb fuel and air adjustments or ????
The bike hasn’t been bought yet. He is just trying to have it kick start ready before they do. Any help greatly appreciated

 

[Pivot]

How long was the gas sitting without flow? The carb can 'varnish' and a simple clean wont fix that. There are boiling methods you can google
Or theres a intake air leak somewhere. Carb base gasket? Cylinder base gasket?

If your trying to buy it id pass

 

[Mr. C]

How long was the gas sitting without flow? The carb can 'varnish' and a simple clean wont fix that. There are boiling methods you can google
Or theres a intake air leak somewhere. Carb base gasket? Cylinder base gasket?

If your trying to buy it id pass

I know it was more than a simple clean. He’s probably still messing with it now so I will wait for him to answer. Thank you.

 

[Rkc]

My dad made the post for me. The carb was taken apart and all parts/jets were put into an ultrasonic cleaner and then the carb was reassembled. (Not by me) but by a close friend who has the cleaner. Bike had a mean backfire when I first put it back together but after a while of adjusting air/fuel screw and idle I was able to eliminate the backfire for the most part.

 

[Your ad here]

Turn the idle adjustment down. Should be a round aluminum piece with a regular screwdriver slot on the lower portion of the carb. There is like a 1/8 turn of adjustment that takes it from headache to normal.

 

[Dettom]

So my son(Little Mr.C) is trying to get this running for his BIL.
Carb has been completely cleaned and torn apart, fuel tank cleaned and fresh gas, new spark plug.
He’s getting a rpm change from a idle to when he runs it a few blocks to a high idle.
Idles fine. Rev it or ride it and the idle stays really high. Also it has a lug ( kinda like a loaded outboard until it clears out.) in first gear doesn’t happen into 2nd.
Could it still be carb fuel and air adjustments or ????
The bike hasn’t been bought yet. He is just trying to have it kick start ready before they do. Any help greatly appreciated

Sounds like an air leak. Four stroke or two?

 

[Your ad here]

My dad made the post for me. The carb was taken apart and all parts/jets were put into an ultrasonic cleaner and then the carb was reassembled. (Not by me) but by a close friend who has the cleaner. Bike had a mean backfire when I first put it back together but after a while of adjusting air/fuel screw and idle I was able to eliminate the backfire for the most part.

Backfire from throttling up in neutral? That is normal for that bike even with proper carb tuning. If it's backfiring going "bang" while riding that is bad. If it goes "poof" that's normal. The air/fuel screw is what you need to focus on. Its tough and takes time. I'm no professional mechanic but service and repaired all my families bikes. 3 YZ250F's and 3 YZ450F's. One of 250's is an 03 and had what you were describing and it was the air/fuel screw. They all have the backfire symptom I described but ride just fine. If it has and aftermarket pipe and factory jetting that will cause bad backfiring.

 

[Rkc]

Sounds like an air leak. Four stroke or two?

4 stroke

 

[Dettom]

4 stroke

I’m still thinking it’s running too lean. Normally, on a 2 stroke it means an air leak. Not so simple on a 4 stroke. But still a carb issue or manifold to carb issue. IMO. Good luck dude..

 

[Rkc]

Backfire from throttling up in neutral? That is normal for that bike even with proper carb tuning. If it's backfiring going "bang" while riding that is bad. If it goes "poof" that's normal. The air/fuel screw is what you need to focus on. Its tough and takes time.

Yes. When I’m neutral and I throttle up it would backfire really hard at first. After messing with air fuel it’s not as much. And almost none while riding. But will still spit a flame out of the exhaust with a high rev, even with a spark arrestor. I know carb work is tedious and takes time. Small adjustments at a time.
The weird part to me was the lug through first gear. Almost felt as if someone was tapping the brakes. But no change in rpm while it happens, and it doesn’t happen at all in 2nd. Havnt clicked higher than that cause I’m at home and the neighbors have kids that play out front.

 

[rmarion]

still sounds like a carb issue...

did you run a fine wire thru the jets??

if there is gunk/crud in the jets... carb cleaner will not remove this ...

good luck

 

[Your ad here]

Yes. When I’m neutral and I throttle up it would backfire really hard at first. After messing with air fuel it’s not as much. And almost none while riding. But will still spit a flame out of the exhaust with a high rev, even with a spark arrestor. I know carb work is tedious and takes time. Small adjustments at a time.
The weird part to me was the lug through first gear. Almost felt as if someone was tapping the brakes. But no change in rpm while it happens, and it doesn’t happen at all in 2nd. Havnt clicked higher than that cause I’m at home and the neighbors have kids that play out front.

If it ran without issue prior to what I'm assuming is storage then focus on the air/fuel and idle. Spitting flames out the exhaust happens, even with a spark arrestor.

 

[monkeyswrench]

Fire out the pipe would usually be from a rich condition, or a spark condition. If it was jetted proper before, and you cleaned and reassembled, should be good there assuming you didn't change altitude (like for me at 5800ft) check the leads, the grounds and the connections for the spark box, make sure nothing got tweaked when pulling tank and carb.

 

[Rkc]

it sat for about three and a half years. Last time it was ran it was all good (close friend giving me the bike). I’m probably headed out to the desert tomorrow. Might bring it with me and run it for a little and mess with it as long as any of these issues won’t cause more damage.

 

[yz450mm]

it sat for about three and a half years. Last time it was ran it was all good (close friend giving me the bike). I’m probably headed out to the desert tomorrow. Might bring it with me and run it for a little and mess with it as long as any of these issues won’t cause more damage.

It has a clogged jet or passage in the carb.. No amount of trying to run it hard is going to clear it out, and carb cleaner and ultrasonic cleaners will not remove stubborn fuel varnish.

You need to completely pull the carb out, disassemble every jet, and physically blow them out with air or run a fine wire through each one. Then verify with a flashlight that there is nothing left obscuring it. While you have it apart, get a seal kit and replace all the seals. Lastly, check the fuel screw on the bottom of the carb, if you are too far in or too far out then you will be trying to compensate with the idle knob, which will throw everything off. If I remember right, that fuel screw also has a small o-ring on it, which can give you idle problems if it is not in good shape.

 

[Boatymcboatface]

The diaphragm usually causes the delay you’re taking about. I actually ran a crf diaphragm on my KTM to eliminate the lag you’re seeing. The rubber could be torn or just to brittle.

 

[Dan Lorenze]

I know these carbs pretty well as I have had multiple Yamaha four strokes. I haven't read the whole thread. Almost always it's the pilot jet/circuit, especially when these bikes sit, they just get clogged. You have to run a wire through all the passages to unclog the jet, the main too. You have to do a really good job at this. I stopped cleaning out jets and just buy new ones as they're cheap and new ones are perfect. Other than that, there is thin plate on the slide that it's easy to install upside down, make sure it's not upside down. The air screw at the bottom should be about 2.5 turns out, and if someone took that apart there's a good chance they lost the little washer and o-ring that go on the needle of the air screw mixture circuit. I would also inspect the float valve and make sure it's operating properly. I highly doubt it's anything other than the carburetor. The worst thing you can do is let these carbureted bikes sit.

 

[Bpracing1127]

The backfiring is normal on these bikes in neutral. Put it back to the way it was.