OzVMX Forum
Clubroom => Tech Talk => Topic started by: noisy toy on June 26, 2013, 10:00:22 am
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Hi, does anyone know what the cause might be for a 83 Honda cr480 throttle to stick? Twist grip like new, brand new cable, slide and carb body look fine. Has original Keihin round-slide.
an interesting ride when you are stuck on full throttle and the kill switch is a waste of time!
I have heard of the slide guide pin having issues, any thoughts?
please help before it kills someone! :-\
cheers.
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I think you will find that the throttle housing needs replacing. I had the same issue that didn't end well.
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Mmm that de be interesting, not much fun I'd imagine.....
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thanks 090, does anyone know where i could source a new housing?
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You need to get a complete new aftermarket throttle assy. There are heaps on eBay.
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do you mean a complete carby or throttle slide?
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do you mean a complete carby or throttle slide?
The throttle assembly is on the handlebars nowhere near the carby...
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"throttle assembly" is new and returning fine, seems like the "throttle slide" may be sticking in the housing.i have heard the plastic slide guide pin can sometimes cause issues but i dont know what the fix is?
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"throttle assembly" is new and returning fine, seems like the "throttle slide" may be sticking in the housing.i have heard the plastic slide guide pin can sometimes cause issues but i dont know what the fix is?
It is the plastic slide and housing. Again the fix is to buy a whole new assembly...
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Get a Domino two stroke throttle, same as on the current model KTM two strokes. $99 retail. Not cheap but neither is your we'll being.
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You will find that it is possibly the carb being worn if it is building revs and the throttle is not stcking then it is defiantly a carb that you should replace with a new one.
#8
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'does' sound like a carb problem rather than a twistgrip one. Might have to think outside the square if the normal tricks don't work. Sounds like you've covered the obvious so ummm, is it really sticking or not say a partially blocked pilot jet, then idles been turned up to compensate [when cold] then it warms up & won't slow down far enough at the first corner [ok maybe not that]!! If it's physically sticking you should really be able to feel it just by drawing the slide up & feel it return minus the spring pretty much. I'm assuming it's a heavy brass slide? but if those big carbs had an anodised or teflon coated lightweight slide well--ditch it & get a chrome/brass heavy type. [or get a later 'flat' slide carb if allowed in vmx--think not]. Finally, hasn't got a bad case of a leaking crank seal on the magneto side?--or sucked a base gasket in causing very lean running, maybe sort of running on when throttle shut off at end of straight etc. All clutching at straws ideas without being 'johnny on the spot' but hope you get it sorted. I'll be having nightmares of my 490k sticking on full song now. My thought for the day. Cheers.
ps, not really relevant but going back 45 years to my DT1, if the 'bolt up' type carb flange wasn't flat or had been overtightened & warped things, the slide [anodised type] would stick just from the carb body going out of shape--plus the anodised slides don't like water or moisture, had that problem back in the YZ80 days so fitted the heavy slide from one side of the yamy R5 350 twin & no more problem.
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My old XT 500 on methanol has a problem with the slide getting sluggish on return after two or three races and sometimes allows the outer cable to jump out of its end retainer. This is made worse I think with the quick action twist grip.
Before each race I now open the throttle fully (engine stopped) and slam it shut.
If I dont hear the slide slam shut I spray a squirt of carby cleaner through the carby throat.
I think its sludgy gunk from emulsified condensation,plus fuel plus a tiny bit of oil blow back.
cheers pancho.
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nother story--not even bed time [alcohol fuel] reminds me when i ran alky [shell racing spirit special--purple] in my DT2 as had no race kit for that so used the high com head from the DT1 kit but ran the oil [shell M or super heavy by memory] ran it through the pump which puts it entering past the carb rather than through it, consequently the slide used to stick, [yellowish anodised slide], think it sort of left a dry powdery deposit but maybe not. So mixed the oil with the fuel & that fixed it straight away but did have trouble with the oil not mixing on cold days--just went milky, used to put something with it to fix that but not sure what.
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Acetone.
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When does it occur? All the time? Only when hot? Pull the carb off, leave the cable connected and make sure the slide is definitely snapping shut?? Is there to much free play causing the cable to pop out of the top of the housing? Is it sucking air, causing it to run lean and pick up revs?
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Acetone, that'll be it. I'm sure i saw or heard on the news the other night that acetone's involved in 'drug' making, suppose you have to fill out screeds of paperwork & have your mug shot taken just to buy a bottle nowdays, bloody hell--what's happening.!!