06 yz 450 Missing when at steady throttle? Help???

Edited....I see the others have covered the potential causes quite adequately.

Good luck!:excuseme:

I am not sure if you guys are familiar with Burned (Eddie Sisneros) But he is the one that reccomended for me to disconnect the tps on my 07 YZ450. He said it will have no effect on performance

That statement is ridiculous. Disconnecting the TPS is causes a dramatic reduction in power. This is not an acceptable fix for anyone who values performance. Try it yourself...

That statement is ridiculous. Disconnecting the TPS is causes a dramatic reduction in power. This is not an acceptable fix for anyone who values performance. Try it yourself...
The TPS has an effect on performance, but only on part throttle performance. It provides load information that allows the timing to be advanced under lighter load/higher speed conditions, and this is intended to improve fuel economy and overall sharpness.

However, the system is designed to operate safely with a failure of the load signal, and because of this, minimum TPS voltage occurs at full throttle. This way, if the TPS is detected as faulty, the system will revert to a failed mode and ignore the signal, substituting a "full throttle" timing map based on rpm only. Likewise, if the circuit opens, or is disconnected, the same thing occurs; the map assumes full throttle, and goes by RPM only.

Thus, there is no difference between normal full throttle behavior and that which occurs with the TPS disconnected, and there is no loss of full throttle power or performance.

I'm afraid it is your statement that is in error, my friend.

"He said it would have no effect on power..."

Again, that statement is ridiculous. The difference is night and day on the track. Don't take my word for it though, or Gray's or Eddie's or anyone else's. Try it yourself.

Read through the post in the link below, my bike is doing the exact same thing at steady throttle and contant speed. Im going to try out the solution in this post over the weekend. I have been hunting for answeres since the day this started which was out of the blue as well. The post details everything this bloke tried then what he did to fix it. Hopefully it will save some headaches like the one ive got after playing with my jetting for hours on end.


Mine does it too but ONLY under part very slight throttle cruising. Not under load at all.

Mine does it too but ONLY under part very slight throttle cruising. Not under load at all.

Mine too. Must be a very common problem.

I suppose mine would be a slightly lean condition if I am slightly missing under very small throttle openings with no load. Is this correct? Not worth it to me to fix just wanna know. That would be my pilot though right?

Quite often, assuming there is no fault with either the TPS or the vacuum release plate on the back of the slide, the problem can be addressed by using a needle with the next smaller upper (straight) portion. These are listed in the tuning section of the manual. The pilot can be used to influence the issue, but should not be used that way at the expense of proper idle jetting.

I had this problem a while ago cleaned the carb twice, and was still happening. I replaced the hot start boot with a steel pro circuit one ($30) and replaced my exhaust washer and that seemed to do the trick. It ran considerably better and smoother.:thumbsup:

Well the answer to the question was the TPS sensor, I was told to unplug it. I did that and my bike ran great. Since then I have sold that bike and got a new Motoconcepts bike. Absolutely love it.


bought my 06 yz450f new. it wouldn't even run. somthing about passing epa, yamaha had to jet it a certain way. read a thread on TT . I followed the suggested fix - changed the main and pilot ( i think) I also got an ajustable air screw. this totally fixed it.

Thought I would give everyone a bit of an update on where I am with this hesitation issue, still haven’t found a solution but have crossed quiet a bit off.

It is a very strange hesitation issue:

At low revs with load is does not have a clean smooth rise in rpm, hesitates in low revs where all the grunt of the 450's usually are for trail riding. When I say it hesitates I mean it jerks and misses as accelerating. Ones it gets to a higher rpm it smooths out, roughly guessing at about 3000-4000rpm from the engine noise.

Then there is the hesitation at constant throttle and constant speed, this is the strange one. It will cruise along at a smooth engine rpm then all of a sudden just die, with no power, exactly the same as when a bike has no fuel and you try to roll start it, makes that real boggy low tone noise. So it cruises along smooth for about 4-5 seconds then will bog for 3 sec or so, or until I get aggressive with the throttle and it kicks back in. It is quiet strange and very annoying.

I first noticed the hesitation on the third ride after purchasing the bike. At the end of the second ride it was getting hard to start so I checked the intake valve clearances which were at zero. Shimmed them to spec and started noticed the hesitation since. I thought I must have put it back together wrong when shimming the valves. Pulled the cam cover and chain and rechecked everything, all seemed in order but the valves clearances had tightened up again. This led me to believe the titanium intakes were wrecked.

Things I have tried to fix the issue include what is listed below. All these points listed are suggestions from other threads on thumpertalk:

1. Valve clearances

Ended up replacing the titanium intake valves with a ferrea stainless set. These were installed by a bike mechanic and were seated and installed with the correct springs and retainers for the stainless valves. Anyone know it worn exhaust valves can cause weird hesitation issues? Last time I checked they were in spec.

2. Jetting

I played around with the stock jetting, changing the clip position, pilot circuit, AP circuit. These seemed to have little effect on the problem. I then bought a JD jet kit and this has smoothed it out a little but no where near 100%, description of hesitation above is still occurring. I replaced the needle guide, checked the plate that sits over the slide and still had no affect.

3. Checked electrics and Stator

I cleaned the stator and removed some small metal shavings, only a small amount of shavings were on the stator, supposedly metal shavings can cause erratic engine characteristics. I also checked all cables to ensue there were not any broken connections, none were found. I have not checked the ignition coil itself and don’t want to start purchasing all the electrics side just for trial and error swap outs, will get expensive.

4. Checked the exhaust for leaks

I have made sure the exhaust is properly fitted and there is no chance of air being vacuumed back into the cylinder causing issues.

As the problem seemed to rise when after shimming the original titanium valves, has anyone had issues after pulling the cam cover, chain etc? Will a bad seal around the cam cover cause any hesitation issues? Im getting close to exhausting all solutions and any valuable input will be much appreciated. I have hear quiet a bit about diconnecting the TPS although this will decrease engine response and is something I want to avoid. Will disconnect it and test to see it it makes any difference in the meantime but I dont have confidence in this being the solution.

I had a 06 and it started some of the same issues. Turned out to be the coil. As in coil spark plug cap combo. What had happened was instead of taking off the tank to get to to the plug I would just kind of force it off and back on. It messed it up enough to start causing problems. If you can get it to run bad at idle then push around on the coil/plug cap and see if that makes a difference. Or, swap it out with a friends. It snaps off and on easy.

where is the TPS located

The tps is attached to the carb. It has a wire with a male, female plug on it that sits under the gas tank. Make sure to try this, it really works. My friends yzf 250 07 had the coil go bad, it just stopped running. If you still can't find the tps check your manual it shows it clearly. If you don't have the manual you can download here on site.

Thanks people,

Yeah I'm starting to think it has to be one of the main electrical components, need to find someone to swap parts out with otherwise I will be spending too much on simple trial and error. The hunt begins I suppose.

I have had similar responses saying it could be the CDI, stator and coil. Will post back if I find a bike and start the swap over.

OK.... I thought I should post what I found with the electrics to save some headaches for people having similar issues.

I got the electrics tested, this includes the wiring harness, spark arrester, CDI, and stator. The bike mechanic tested everything and had a feeling the stator might be shot. Ended up sending the stator to a more knowledgeable electrics person and they found that one of the stator poles was reading a low voltage, or in other words was faulty.

The pole is now getting re-wound and I should receive it within 7 days.

I am fairly confident that this is the fix to my issue. Will confirm this once I put it all back together and see how it runs.

So for people having a hesitation issue that seems to be carby related, it will pay to rule out the electrical side of things if changes in jetting does not fix or alter your hesitation. I have heard of faulty stators, CDI’s and spark arresters being the problem for hesitations or bogs that are firstly diagnosed as jetting. Jetting is cheap to changes, electrics get expensive, best to start with the jetting before swapping electrics. However, testing the electric is real cheap if you pull them and take them to the bike shop without the bike, only cost me 20 aussie dollars.

A couple of things I noticed about the bike performance that might help assume an electrical problem is present:

1. As the motor warmed to normal operating temp the hesitation issue seemed to become more noticeable. So when it was cold it ran better, when warm it ran worse.

2. When cruising at a constant throttle position and a constant speed the hesitation was present. This hesitation at constant throttle and speed was more noticeable during the higher gearing (4th-5th). When cruising it will feel normal for 4-5 seconds followed by cutting out for 2-3 seconds before the power kicked back in. This would simply repeat over causing jerky riding. When it cut out (hesitated or bogged) it was like it had no fuel, or like the kill switch was held in.

So hopefully this might help others fix this hard to find and hard to diagnose problem. If you read my other earlier post it explains what I had gone through to fix this hesitation.

My hesitation problem ended up being a combination of adjusting the needle clip, shimming the intake valves to the loose end of the spectrum, and re-jetting.

Also noticed my YZ is really sensitive to cooler conditions....tried riding in the cold winter and the bike didn't like it at all. It would hestitate bad, snarl, pop, and puke sounds going partial throttle. When it is warm out, she runs like a champ.

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