high/sticking idle, jetting problem?

22 replies to this topic

Posted December 25, 2005 - 01:12 PM


ok, so when im riding, and i let off all the way(to stop or slow down or whatever), the idle stays up a little high. if i blip the throttle, it usually goes up a little, then after about 2-4 blips of the throttle, the idle will come down to normal. and if im at a stop, in neutral, if i give it a little gas, the idle come up just as i explained and i have to do the same to get it to come down. also, it will come down, but after quite a while, definately nothing normal. is this a jetting problem? im not sure where to start if it is. i am probably going to clean my carb right now and maybe that will help but if it may be a jetting issue what do you think it could be? thank you.

  • new2blue450

Posted December 25, 2005 - 04:20 PM


i had the same prob with my 04 450, and i sprayed (lubed) the cable and the just rode it, and it stopped....i also posted the same question. do a search on it if you want more opinions.

  • Chopio

Posted December 25, 2005 - 05:53 PM


Did you put the slide plate in upside down?

  • MN_Kevin

Posted December 25, 2005 - 06:03 PM


you can also try turning your fuel screw out. It may be running lean (or an air leak?)

  • biznet1

Posted December 25, 2005 - 06:05 PM


I think it would run much worse with the slide plate upside down. First, when you stop, rotate the throttle to the minimum postition. In other words, make sure it not something in the throttle tube preventing return. Second, check you throttle cable by removing the plastic cover over the throttle cam next to the carb and see if it's frayed or binding. Next, Lube the cable using a good cable luber to make sure it's not sticking. Clean your carb very good. Check for clogged jets too. If none of this fixes it (which, by the way, is a good preventive mainenance procedure anyway), then start working on jetting.

  • greyhd

Posted December 25, 2005 - 07:46 PM


Was your jetting right before?

You most likly have lean jetting with temp changes, air leak or a tight valve. As stated start with your fuel screw.

  • yzf450jack

Posted December 25, 2005 - 08:49 PM


Check your hot start cable it may be loose at the carb. Or cracked intake rubber I don't think it would be the cable it's a push-pull throttle

  • grayracer513

Posted December 25, 2005 - 08:57 PM


Greyhd is the only one who's mentioned it: check the valve clearance. A tight intake will do that. It's not the only thing, but it will.


Posted December 26, 2005 - 12:03 PM


ok, completely cleaned the carb, lubed the cable(new cable anyways), checked for any air leaks, and it still does it. my jetting was pretty good before, im going to check the fuel screw in a little to see if that could be it, then i will have to get down to checking the valves.

also, another random quick question, i unplugged my TPS and the bike seems to be running good still. has kind of a choppy idle but throttle response seems really good. i know ive heard of this before but cant remember what it does. is it alright to leave it unplugged and what advantages/disadvantages does it have? thanks again for all your help.

  • MN_Kevin

Posted December 26, 2005 - 12:45 PM


also check your float height. If anything, it is too low.

As for your TPS, I seem to recall that in the early 2000's, guys were disconnecting their TPS for a (supposed?) good reason...

As for your fuel screw, too lean means you must turn the screw out >> more fuel.

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Posted December 26, 2005 - 01:46 PM


i still have yet to mess with the fuel screw, but i did take it for a spin around my block, my neighbors love me, no :applause: . but the bike runs really good, seems to be a little snappier with the TPS unplugged. but about the idle problem, i will richen it up a little and see how works. but, im pretty sure im completely lean right now, the temp is definately down from what it was last time i rode. its currently 58 right now, last time i rode it was 70, and at a higher elevation. damn, now that i think about it, i need to mess with the jetting before my big glamis trip. oh well, i know that this lean condition isnt affecting it because last time i rode the jetting was pretty on and it still did the same thing. oh well, ill see what i can do. thanks again.

  • WR TOM

Posted December 26, 2005 - 01:49 PM


Cable pinched?


Posted December 26, 2005 - 04:51 PM


no, doubt it. dont see anywhere it could be pinched. also, when it does high idle, i can turn the throttle all the way to closed and it still does it. so im almost certain that it has anything to do with the throttle cable.

  • grayracer513

Posted December 26, 2005 - 05:47 PM


The TPS provides the CDI with information to use in mapping the ignition advance. Back in the day, the timing was fixed; you set it at one point, and it stayed there. Not very sophisticated, and something that would never work on a modern 4-stroke with the rev range they have.

Next, there were CDI's that used a tach signal to advance the timing to match the engine speed. Much better, but such a system still ignores the fact that the engine will run cleaner and sharper at part throttle if we can also advance the timing some more when the throttle is partly closed. That's where the TPS comes in. The CDI unit advances the timing based on RPM, and then moves it around to match the throttle position.

If you disconnect the TPS, the system sees full throttle all the time, and maps the timing curve accordingly. Full throttle performance should not be affected, but part throttle will, and you may or may not like the results. One of the things this is supposed to cure in the '03 450 was a mid rpm "hit". Dyno tests showed that the hit was actually a sag in power followed by a sudden return to normal. Mine never had it, and I found out by experimenting with the exhaust that it wasn't there because the power bomb header had already gotten rid of it, so there's more than one solution. My vote is to leave the TPS alone, and in any case, it will not cure your idle problem.

  • PumpkinHumper

Posted December 26, 2005 - 06:17 PM


Check your valve adjustment. Tight valves will cause the idle troubles you are describing.


Posted December 26, 2005 - 09:07 PM


the question about the TPS wasnt related to the idle problem at all, just a quick side question that i wanted to ask without starting a whole new topic. thanks for the info, seems to be fine with it unplugged so i will see how it runs then go from there.

as for the idling, richened up the fuel screw and didnt really see much of an improvement, got a little late to be messing with my bike(kinda loud), so i will see if i can mess with the fuel screw a little more tomorrow as well as checking valve clearances. as always, thank you all very much for your help.


Posted January 05, 2006 - 10:19 AM


so i finally checked my valves the other night. exhaust were right on but the intake were way too tight. i couldnt even get my smallest feeler in. so as soon as the shim kit comes in ill be fixing that problem.

ok, so since ive found that my valves are tight, they've definately got some hours on them, should i think about replacing my valves soon to prevent any possible future problems? i was kind of thinking about kibblewhite black diamonds and their spring kit as well. anyone with any experience please let me know what you think. thanks again for all your help.

  • grayracer513

Posted January 05, 2006 - 10:54 AM


ok, so since ive found that my valves are tight, they've definately got some hours on them, should i think about replacing my valves soon to prevent any possible future problems? i was kind of thinking about kibblewhite black diamonds and their spring kit as well. anyone with any experience please let me know what you think. thanks again for all your help.

What you may find is that your valves have actually gone to, or even beyond, zero clearance. This will show up if you end up with a shim .15mm smaller than the one you took out but still don't have at least .15mm of valve clearance. It happens.

Either way, if you have had to shim .10 or less to get back to spec, begin checking your valves more frequently to see if they will hold their adjustment. If you need to go .15 -.20 or more, start planning to redo the head as soon as possible. With that much wear on them, the valves no longer have any hard coating left, and will wear very rapidly. If they wear eccentrically, they will experience a bending load at the stem as they seat, and that can lead to the stem failing.

Read this post for confirmation and some images you don't ever want to see IRL.

Here are some pictures of Worn Valves at different stages.

Use stainless valves if you want. I don't think that you'll find them anymore reliable than the OEM Ti valves, though, and I have seen some negative comments on them. The bad reports could well be the result of improper seat preparation, though. Remember that stainless valve need springs made for the purpose, and the Kibblewhite kit is expensive.


Posted January 05, 2006 - 05:38 PM


what valves would you recommend i use? i figured that i should probably upgrade to aftermarket valves and i thought that kibblewhites were good. maybe i was mistaken. any input on this would be great. im going to adjust them, see how bad they are, and try to hopefully make it through one more glamis trip next weekend.

  • grayracer513

Posted January 05, 2006 - 08:19 PM


Differing opinions exist on Kibblewhites. I have not tried them myself, but I do get excellent service from the stock Yamaha valves. Purchased through the TT OEM parts store, the price is much better, too.

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