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Idle Problems???

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For the past several weeks my xr500 has been holding high RPMs after cracking the throttle or accelerating. At first i thought it might have been the slides sticking or something carb related - but after spraying out the slides and cleaning the jets the issue remained. I've also checked for air leaks in the boots and cleaned the throttle cables with no luck.

I've noticed, however, that the bike will stop holding RPM's when i back off the idle screw (or at least hold for shorter periods of time). Only problem is the bike wont idle backed off this far. Any suggestions? I'm at a loss...

Thanks!

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Thats what i thought, but why would turning the idle up or down affect it? Any idea where to look?

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What year bike is this. May pay to put the machine you own in your signature so we don't need to ask. I'm assuming its the 83 RFVC model. You said you lubed the cables but have you checked them for any binding on their route to the carbs. Any sort of bad routing can affect their performance..We also assume you have taken the Accelerator mechanism on the Handlebars completely to bits and checked and lubed it and also made sure it's not binding on the tip of the bars..ie it has the mandatory quarter inch gap between the end of the bars and the actual housing. Did this problem suddenly just start occurring or have you had the carbs completely separated from one another at some time previous to the issue..??? I might just add that you should put a new Spark Plug in her and then retune the carb..maybe it's just so far out of what it should be air screw wise that the idle adjust screw isn't really even close to being where it should be for the amount of air or lack of air thats getting into the carb..I'd also be checking any electrical wires around where the accelerator cables connect to the carb to make sure they aren't impeding the operation of the mechanism ,,

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If you can't find an air leak around the intake or exhaust ports, it could be a valve issue. That's the way my bike ran when it had a stretched cam chain.

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Thanks for the good ideas!

Horri, the bike is an 83 RFVC just like you said (sorry for not mentioning that earlier). Cables and housing are all adjusted properly, free from obstruction and lubed etc. The issue began prior to any work being done to the carbs and ive never had them separated completely. I also replaced the plug about a month ago. It is possible, however, that the carbs need tuning (perhaps major tuning) - its just curious how this began without having made any changes to the bike.

uranys, thats also a definite possibility. The engine makes a lot of noise even after my valve adjustment and i'm beginning to think it might be the cam chain tensionor. Could that cause this to occur?

Thanks

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Quote::: i'm beginning to think it might be the cam chain tensionor. Could that cause this to occur?

I wouldn't think so. Seems you've covered all the likely scenarios that'd cause the thing to overun. Dunno what to suggest really..All I can say is carb kits ain't cheap for the twin carb bikes. Sooner someone fabricates a flange so we can go from the two to a single carb the better. It's something I've looked at but shyed away from due to my not being an engineeer/machinist..Maybe check all the overflow tubes are clear of obstruction ,,bout the only thing I can think of that could cause some weirdness..

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Yeah someone ought design a single carb conversion for these things - it would make life a whole lot easier. Would you happen to know if a later model single carb xr600 engine would work in the old 500 frame? Just a thought...

Thanks for all the suggestions. Hopefully i'll have some time this weekend to mess around with it. I'll post again when i know more.

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Quote::: Would you happen to know if a later model single carb xr600 engine would work in the old 500 frame? Just a thought...

Can't say a 100% as I've only put the older 83 XL600 engine into the 500 frame so I didn't get involved with the single carb . I'm certain the Motor will fit it's just the issues to do with the positioning of the Shock mounting point on the twin carb models and the use of the single carb with it that I am unsure about..Airbox would plainly need modding..Tomorrow I'll study the intake manifold on the twin carb and the intake from a single and see what I can come up with in the way of changing things..Don't hold your breath though as I've looked at them before and run a mile. May have some sort of brainwave if I spend enough time pondering it while I skull an Ale.:) .

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I have the exact same idle issue in my 83 xl600r, and if I put tension on the throttle to hold it shut it idles down, even though the throttle assembly doesn't appear to move anymore. So I adjust it so the normal idle is high and when I close the throttle hard it idles ok, or the normal idle is correct but it dies when pressure is applied to the throttle. Both my carbs have been cleaned and rebuild (kits for both, did it myself) and the idle jet bumped up. Also brand new throttle cables (old ones wouldn't even return shut). So I am also trying to figure out how to even out the idle (unfortunately my buddies 86 XT600 idles amazingly well :thumbsup: ) Only thing else really done to it is an FMF Q and Uni intake, with the airbox opened up a bit, I have a new iridium spark plug and regular plug for it (they didn't make a difference) and spare stator, pulse generator, 3 coils, and a CDI, the CDI hasn't really done anything mine and the spare seem to work the same. Hopefully once the weather clears up I can start opening it up and figuring this out.

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