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Discussion Starter #1
Hi everyone,

I just bought a used ogm140 and it came with a mikuni vm26 carb with the pull choke on the side.

I finally got the engine started today after fixing some problems with the old cdi.

When I start the engine with the choke on (pulled out) it seems to idle fine other than maybe being a little low.

When I turn the choke off the engine revs up fairly high (like it should when the choke is on) for about 4 seconds and then the idle drops, it backfires twice, and then stalls out.



What should I do?

Is it the fuel air mixture? main jet size?



the main jet is at a 165.
 

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Discussion Starter #3
roaoro said:
sounds like an air leak somewhere...


the manifold and everything is tight and def. isn't leaking....... could there be a leak inside the carb itself?

what would I check, how would I know?
 

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Air leaks can be hard to detect, especially if your bike won't idle to begin with. If you can get the bike to a steady idle, then you can spray some carb cleaner, starting fluid, wd40, or something similar, around the intake and carb bowl. If there's a leak, the motor will usually either speed up or down when you spray. One other thing to check is make sure your throttle cable isn't sticking, and your spring in your carb is pushing the slide down properly. Your float could also be stuck, letting fuel over fill in the carb. Good luck.
 

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Discussion Starter #6
roaoro said:
Air leaks can be hard to detect, especially if your bike won't idle to begin with. If you can get the bike to a steady idle, then you can spray some carb cleaner, starting fluid, wd40, or something similar, around the intake and carb bowl. If there's a leak, the motor will usually either speed up or down when you spray. One other thing to check is make sure your throttle cable isn't sticking, and your spring in your carb is pushing the slide down properly. Your float could also be stuck, letting fuel over fill in the carb. Good luck.


thanks for the advice man..... but I kinda solved the problem. I had to change the main jet to a 175 and I had to move the C clip on the needle to the 2nd from the bottom notch.
 

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Discussion Starter #7
need some TUNING TIPS now.



when I'm riding it and go to crank on the throttle it bogs slightly. how do I fix this???
 

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You need a larger pilot jet.. 17.5 a 20 or a 22.5 see what size you have in there and go up 1... It should be one of these 3...
 

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Discussion Starter #10
taz69 said:
You need a larger pilot jet.. 17.5 a 20 or a 22.5 see what size you have in there and go up 1... It should be one of these 3...


so how do I know what size it is???? all it says on the needle is 5E75
 

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Discussion Starter #11
taz69 said:
You need a larger pilot jet.. 17.5 a 20 or a 22.5 see what size you have in there and go up 1... It should be one of these 3...




how do I know what size it is??? the only numbers on it are:



332 [] 0-0
 

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The jet on the left in the pic below is what your pilot jet should look like, the only numbers on it should be the jet size. The number you posted above was for the emulsion tube, or needle jet, which is where the main jet sits. It is part #26 in the second pic shown below. Parts #24 and #27 are the pilot and main jets.









 

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Discussion Starter #13
haha, alright thanks man :)





I pulled it out and its a 17.5..... so if I buy the 20 it will fix my problem right?
 

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Discussion Starter #14
[quote name='dirtbkr188']The jet on the left in the pic below is what your pilot jet should look like, the only numbers on it should be the jet size. The number you posted above was for the emulsion tube, or needle jet, which is where the main jet sits. It is part #26 in the second pic shown below. Parts #24 and #27 are the pilot and main jets.







haha, alright thanks man




I pulled it out and its a 17.5..... so if I buy the 20 it will fix my problem right?
 

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Discussion Starter #15
dirtbkr188 said:
The jet on the left in the pic below is what your pilot jet should look like, the only numbers on it should be the jet size. The number you posted above was for the emulsion tube, or needle jet, which is where the main jet sits. It is part #26 in the second pic shown below. Parts #24 and #27 are the pilot and main jets.




haha, alright thanks man




I pulled it out and its a 17.5..... so if I buy the 20 it will fix my problem right?
 

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Discussion Starter #17
dirtbkr188 said:
Pick up the #20 and the #22.5, just to have. That way you won't have to make two trips in case you need to go bigger than the #20.


thanks a lot bro, i'll try it out and see how it works for me.
 

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Also ... check your valve clearances to make sure they're OK as a lack of clearance can allow blow back thru the inlet tract which can mimic carb problems ...
 

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Pat Farsole said:
Also ... check your valve clearances to make sure they're OK as a lack of clearance can allow blow back thru the inlet tract which can mimic carb problems ...


Exactly,,,,Tight valves will cause lean running symptoms. Idle hanging, stalling etc.
 

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Have you tried adjusting the AIR SCREW? (#17 on the diagram)



Try that before changing the pilot jet. Start a 2 turns out and adjust it to in or out a half turn at a time to see if it runs better.
 
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