Something causing unwanted WOT

[86Rrider]

I've got one that is puzzling me some and I hope you guys can help point me in the right direction here:

Problem: on steep up-hill climbs or landing jumps, engine will rev to the moon with no throttle control. Get engine shut down (kill switch or locking brakes to stall it), restart and runs fine until next hill or jump.

What I have found: 3 occasions now, while out riding when this happened, I've pulled the filter to carb boot and found a lot of residual 2-stroke oil laying in the boot. The filter side of the carb is very wet looking, slide and other parts look OK. Well that is except for the large wear-marks on my slide. The last time this happened was this past Saturday at the MX track during practice. This time I found the needle down in the jet bore, no longer in the slide when I took it apart. When I took the slide-cable apart, I found the circle clip but it was "un-folded" where it would go on the needle. I got another clip from a friend and put it back together. Second jump it did it again! My buddy had his stock '89 with him, so thinking that the worn slide might be it, I took the slide out of his 89 and put it in mind. Now, mine is not running well and wants to die when the throttle is opened. So, I swapped all the parts back and loaded my machine on the trailer!

OK, what I have: '86 with stock carb, Boyensen Rad valve with the fiberglass reeds, 10mm over-bore from stock, very mild port work, Uni foam filter.

I have not removed the carb and tore-into it yet. I'm kind of thinking I might have a float or float valve issue. Or do I have some other major issue here that you guys have seen before?

[JohnBeton]

I think your engine is leaning out because you're going uphill.
That's also why the fuel runs to your airbox.

[Motofool250r]

i have a spare stock carb if you want a parts carb, maybe it works out for ya.

otherwise i suggest new carb

[RyanWsly]

Make sure that little spring loaded holder is in good shape, the thing you twist in to the slide to hold the needle in place where the throttle cable attaches. The sides wear off of them where it is held in by the slide.

[86Rrider]

OK, I had the time to get into things last night- I pulled the carb loose from the engine and intake boot, turned it so I could see in the bore good and worked the throttle. I did not see any binding/draging of the slide. What I did notice was that the needle was moving in and out at an angle? As the slide went up, the needle moved off to one side, then when the slide went down, the needle straigented back up. Pulled the slide/needle/cable assembly off the carb and took apart. RyanWsly- from best I can tell, the needle retainer looks fine, no wear on the "ears" that hold it in the slide, as well as no real wear marks on the brass cap that has the spring on it in the bottom of the retainer. What I did find was my needle has a badly worn area about 5mm below the bottom circle clip groove. I believe this would explain the needle "moving" during the slide travel.
Next took the carb apart- no sign of the float needle sticking or crap on it or seat. Did not check the float level, will do so tonight. Inside of carb clean except for the main jet- it is just black! No brass color left on it! Pilot jet is still normal brass color. Is this one of the issues with ethanol laced fuel?

Finally, checked throttle cable. Had a couple of dirt bike guys tell me I could have a frayed cable causing this. Seemed OK to me.

So, as of now, my theory is the worn needle possibly was catching on the main jet or passage and holding the slide open? Any idea as how this happened? Or is this just my lack of experience with carb maintenance or not seeing something like this from not being around racing where I hear wears parts out quickly? Any other suggestions or things to check?

Motofool250r- I may take you up on the offer of that carb. PM me with a price and how you would want to trans-act it.

[265 sleeper]

Also check for some sort of air leak between the carb and cylinder. I've ran into that from jet skis and atvs.

[wolvman]

i am wondering if the needle holder threaded plug that you hook the throttle cable into is excessively worn letting the needle move around an hang up going back down in the main jet .throttle spring an plastic ring good shape also is your thumb throttle spring on the arm in side thumb throttle housing in good shape

[86Rrider]

Thanks for the replys!

What I ended up doing was getting another carb from jamieg45 on here and using that carb bore, and slide. I then installed the float, pilot jet, baffle and fuel bowl from my carb. Put in a new needle, circle clip and main jet. I also tore-down my thumb throttle assemble, inspected, clean, lubed and re-assembled it.

Just got back from putting 290 trail miles on it over the last 4 days and had no problems!

Now, when I was putting all of this back together, the new needle in the used slide, with the "best" condition retainer gave me the least amount of movement of the needle in the slide. Is there suppose to be no movement at all? I'm thinking that there will be some, due to the fact that the needle retainer has the spring on it? Or, do I still have a worn slide? Or a worn retainer?

[bobizzle]

i would highly suggest you buy yourself a cable luber. i use it as preventive maintenance and to keep some life in my clutch and throttle cable.

remember when using it on the throttle cable to disconnect it from the carb. is it is connected then you will have the lube drain down into the slide of your carb.

the luber also helps sticking cables that can act up in the middle of riding.

[wolvman]

I went out an look at a known good working needle an slide gently moved slack to one side then to the other it had 1/8 in play out at the end of the needle so I am going to assume if yor have more play than that it might need a new slide needle retainer saw somewhere maybe eBay they had new retainer an shims to keep needle tight hope this helps

[86Rrider]

bobizzle and wolvman; thanks for the additional info. Sorry, I have not been to the site in a few days to see your posts.

bobizzle- thanks for the recomendation on the cable luber. I was jsut talking with my riding friends this past ride about that. However, as far as life-span of a cable- my throttle cable is the original one put on the machine by Honda in '86. So, I think I got my money's worth out of it. But, since I now have an after-market cable, I definitly want to lube it to make it last as long as I can!

wolvman- my original slide-needle combo had over a 1/8 of movement, but the new needle in the different used slide combo I have about a 1/16 of movement at the tip of the needle. So, I might try the shim idea to try and reduce that more.

[bobizzle]

glad to see the information helped you. just dont wanna see the people have issues with their quads and have a lot of down time. rather be riding that sitting trying to figure out a small pesky problem.