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2006 yfz450 will not stay running after idle.

13420 Views 15 Replies 5 Participants Last post by  filsgood
This past winter I bought a 2006 yfz450 that ran perfect. After sitting in the garage I tried to start it but I would not fire. So I rebuilt the carb and then it fired right up no problem. When I rev it up it takes right off but will not hold any RPMs it runs out of fuel and dies or wants to die as it comes back down from me revving it. I think the accelerator pump is the only thing shooting fuel in the motor after it comes off idle.
I have cleaned to carb many times now and all the passage ways are clear.I even sonic cleaned to carb with no change after.

Now if I hold my hand over 1/2 the air box I can rev the motor and hold RPMs it seems to love it. It is acting like a passage way is plugged but I verified it many times that its all clear.
I checked for air leaks by spraying stater fluid all over the carb and found nothing.
I'm running 168 main 45 pilot 4th clip and 2 turns out on mix
quad is stock, zip tie mod and oil mod

any ideas?
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check to make sure you have free flowing fuel to the carb, is you float adjusted properly. jetting sounds fine. did you get the slide in correctly it will go in backwards. did you compare your new needle side by side with the old one. your machine may have had a custom needle or you possibly got the wrong needle. my 06 had the carb drilled for a bigger needle and factory needles just rattle around in the seat. it sounds like carb but try unhooking your parking brakes switch and bypass your tors and see if that makes a difference. did you change the plug.
I have a free flowing fuel to the carb and the tank breather is not plugged. New spark plug or old spark plug it runs the same. float is adjusted properly and the slide looks fine its square side down with the hole in it. I did not look at the new needle will do that tomorrow. I did unhook the tors and tps and it made no difference. Both the new plug and old plug are turning white and I also get lots of popping from the exhaust. It pops when I am trying to hold RPM or letting off of it. all vent tubes are clear also.

Whats the best way to bypass the TORS? I think thats the one that has the 3 wires and plastic peace that moves with the throttle.
nope the tors is 2 wire harness. the easiest way to bypass it is unplug it at the carb and use a yellow female spade connector on the harness side plug. if you search my posts in the yfz section i did a write up explaining tors and tps if you want to understand it better. every thing you describe says vacuum leak between the carb and the head there is no way you could be that lean with a 168 main. you may have to take it apart and inspect it closer. starter fluid is not always reliable. if the tps is out of spec it will run bad on the bottom end, when it is unhooked the cdi defaults to the wot timing curve but would not cause symptoms like yours
The float needle seats fine with no slop. Are you talking about the long needle that gos to the main jet? once the needle moves out of the main jet it becomes sloppy.

I was thinking it was the seal between the carb and the intake also but after spraying it with starter fluid I dismissed it. After pulling it off and looking at it I can't say its in the best shape but looks like it should still seal. I ordered a new one anyway and will be here tomorrow.

How do you disable the TPS then?

Thanks for the help so far
yes I was talking about the long needle that goes in the main. it will be loose once it lifts. mine was loose when seated. some but not all of the symptoms were similar. mine was popping and back firing but it was due to an extremely rich mixture and fuel collecting in the pipe. mine however was fouling plugs and not turning them white. you would have to do a side by side comparison with the old one to know for sure (assuming you changed it with your rebuild) you don't want to disable the tps in my opinion. one it will not cause the issues you are having and two when you disable it the cdi defaults to the wide open throttle timing curve. making the machine harder to start and reducing performance on the bottom end. checking it is fairly easy if you have a good ohm meter but you will need a manual for the specifications. don't get too hung up on the tors tps or the parking brake switch, they are just simple rule outs to help me rule out some of the electronic stuff. the fact that it ran before parked and now has issues normally says carb. electronics don't normally go bad sitting.there is a spring and diaphragm on the side of the carb, the name escapes me right now. did you check to make sure that is good when you did your rebuild. that can cause vacuum issues as well.
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I put the new carb seal on that go's between the carb and the motor. It helped out a lot. She idles even better and sounds like it has a lot more power now.I had to turn the idle down a little because it wanted to run faster after the new seal was put on. I can hold rpms better but now its popping out of the exhaust 2 or 3 times per second but they are much litter pops. The plug is now a gray color.

I did start with a black plug and 158 main 42 pilot so I feel something is still letting air in.

I have been revving and holding rpms in neutral if that matters.

The only thing I can find on the carb diagram that looks any different then my carb is #32 Plunger, Starter mine has a o ring half way up the shaft on it and the diagram shows a o ring at the bottom of the Plunger, Starter My o-ring is wore real good but feels like it makes a good seal.

part numbers 32 and 34
2006 Yamaha YFZ450 SPECIAL EDITION (YFZ450SPV) Carburetor | Babbitts Yamaha Partshouse
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you said in your first post a 168 main and in the last post you state a 158 main. did you change it or is one a typo. if it is a 158 main i think you are too lean. you should be up around 165. if you have the cash i would order the jd jet kit for it, they are about 80 bucks but i think it will fix the rest of your problems. it comes with a redesigned main jet needle, a selection of jets and instructions that guide your for your elevation and any future mods. it also give you the ability to easily re jet for new riding areas at different elevations. if i am guessing correctly your carb is factory stock. what you describe sounds lean and that would coincide with the factory settings. they are lean from the factory. if you cant swing the jet kit jump up to a 162 or 165 and see what happens. i am running a 170 with a pipe airbox mod and some mild motor work at sea level and i am a little lean. the diaphragm is part 81 and 82 but i think you found the problem and just need to fine tune the jetting. both of my yfz's pop and snort a little when you are holding rpm's in neutral
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I have a 168 main in right now but the carb was stock when I started and it had a 158 main in it.
I made a big discovery today but I dont know what it means yet. If I block off the 2 little holes in the front of the carb on the air cleaner side when its running it starts running perfect. I can rev it up hold rpms no popping. the choke will bog the warm motor down but when I remove my fingers from the 2 holes it starts running like crap. I have to cover both holes for it to make the quad run well.

what does this mean?

I found this out because i tried blocking off the hole air box with my hand and it only made the quad run better. So I then took off the air housing and covered the carb with my had. It died right away.
gas is 2 weeks old. I flushed the tank also
I've had problems like this before and the carb had small particulate inside where you couldn't see it, had ultrasonic solution cleaned and it fixed issue. Not sure that's your problem, just a suggestion.
Interesting to know that Bigsilvey, can you elaborate more about the ultrasonic solution?
are your leak jets in good shape. i am not sure what those hole do but my guess is they are tied to the leak/starter jets somehow. have you looked at the manual to see if you can tell. i have to get mine out of the trailer this week so i will look and see if i can figure it out.
I know this is an old post but I have a 2005 with what appears to be the same exact problem. I have a dynojet Stage 2 kit jetted as they recommend. It only runs well when I restrict the airbox inlet. It doesn’t look like this issue was ever closed out here so I’m hoping you could give the final details. Thx
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