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Dt125G Sticking and Revving on its own

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I bought a 1980 Yamaha DT 125g that was running well before but the carb was dumping fuel out the overflow so I tried replacing gaskets and needle valves etc. eventually I put a new carb on and fixed the fuel issue but now whenever the bike is idling and I try to give it throttle at about 3000rpm the rpms will stick and stay there. When I get it even higher sometimes it will shoot up to 7000rpm after I release it. One time the bike even did it on its own. The only way I can stop it is by turning the bike off completely. It doesn’t feel like the throttle is really sticking and I even lubed the whole mechanism up. Does anyone have a clue as to how I can fix this?

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Sounds like an air leak or the slide in the carb is sticking

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I had something similar when I used an emergency circlip fix (read bodge I was 17) on a gp100. The jet needle was lose and could move and made the bike do some odd things. 

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Hi there, all very familiar!!

have a read of one of my previous posts about my DT....


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Further to the above thread, I also replied with this which you may find helpful as it relates to the airleak i had.....


This idle problem may well be air related, I had a not disimilar problem, albeit it would race away. But mine would not idle properly either until I solved the airleak.

One solution to locate a leak (mine was the bottom gasket) was to make a load of soap suds bubbles and brush it all around the engine with an old paint brush whilst its running, any bubbling will locate the leak.

(A similar method is used to spray WD40 on the crankshaft seal as mentioned before)

Might be worth a go....its only soap suds!!! and you'll clean your bike at the same time!

Edited by NE0
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