Engine runs but won't idle

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Active Member
Greensboro, NC
I was running the other day fine. The next time out I switched by to Coleman camp fuel and Yamaha dirt-bike 2 stroke oil (oil used for several gallons now) at 25:1 ratio. The engine ran the same as always for 10 minutes and then it slowed down over a few seconds and then shut off. I restarted it after a few pulls and ran it again but when I came off the throttle it died again.

I dumped the camp fuel mix and went back to gasoline and oil at 25:1 because that is the only variable that had changed and I didn't have any wrecks on my last outing. I couldn't get the engine to turn over.

Finally I got it going but it won't idle. It just dies if left at idle. I got it going and kept the throttle up and it runs fine at moderate to high throttle but will die if allowed to idle.

I took the carb apart somewhat and did not find any debris on the diaphrams. I put the engine back together and tried it again and it still won't start.

I switched out my plug for a spare CMR7H that I'm pretty sure is a good plug. Both plugs have visible spark if held outside the engine against the head while pulling the starter cord.

The way the engine died off like it did and the way it will run at moderate to high speed I am confused at what I am fighting here. I have not checked for dirt or gapping on the coil yet. My engine is going to be a real pain to remove because the engine screw heads are partially cammed-out.

I did not know how many parts I should remove from the carb because I want to be able to get it back together. I could take it apart again and take off the low and high screws this time. I could soak it in carb cleaner to try and clean it. The diaphrams did not have much debris at all on them, though.

What do you guys think?
I've never switched back and forth but is it necessary to drain all the fuel out then switch to Coleman so there is no jelling? Not at all sure if it happens but its a thought?:blush:
Definitely sounds like a carb issue to me though.
I cleaned up and re-gapped the spark plug last night just in case. I held the plug outside the cylinder again. This time it not only sparked brighter it actually ignited some gasoline vapors. It was kinda cool looking after I got over the initial shock of it :scared:

It still would not start so I flipped it over and used the pullstart to force the excess fuel from the cylinder. I have left the plug out overnight so the rest of the fuel will evaporate. I will be trying it again this evening.

I suppose if it is still misbehaving I will tear down the carb further and give it a more thorough cleaning.

To remove the H and L screws do you just unscrew them completely? Is it just the opposite to screw them back in?
Unscrew them completely. be carefull when you do put them in. seat them gently so you don't screw up the end of the needles.
ya, flattens the needle end or breaks it off and its rebuild and in most cases a new carby lol, as you seat them hard you also muck up the seats. lol
Cool! That is the kind of 'words of wisdom' I was looking for.

So if I take off the plastic plate on top that holds the primer bulb, the cover on the bottom, both diaphrams and the H and L screws, is it ready for a carb cleaner bath? Should I pull off the throttle assembly or can I just leave that in place and get a basic cleaning?

Thanks for the info!

the bottom has a few more parts other than the cap. theres a diaphram and a small needle valve so be careful but ya that SHOULD be it. but its been a long time since i tore into a carby.
I was about to clean my carb when I decided to try and crank it one last time. It started up as if nothing had gone wrong!

The last thing I did was empty out the cylinder and leave the plug out for several days to let the fuel evaporate.

I suppose I was having some carb blockage problem that eventually corrected itself but I was flooding the engine in the process.

Whatever the case I'm up and running again! Thanks for the suggestions guys!
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