jawa 40 - running problem

ok, ive had this same porblem with my jawa for like a month now, and ive elimnated jus about everything...

the problem is this, when its cold, it starts up fine, regardless pretty much of the mixture screw setting. it drives great for about 20 minutes, maxing out at 25. after this, it starts cutting out right at 20 and looses alot of power going up hills. i rev it on the stand at this point, and the high end is awful, it sounds like its not getting gas. (cutting out and misfiring) so i put it away and take it out 20 minutes later and it runs great for ten minutes. it sounded like a gas issue to me, but whenever i pull the fuel line of the petcock, theres a steady stream of gas.

-the compressions fine (120 warm, cold)

-it runs the same with the gas cap unscrewed

my dad thought it might be overheating, although the fins are clean... the other thing is ive been running it with out the air filter lately, the foam thing discintegrated and was getting sucked into the engine.

thanks for any suggestions!

Re: jawa 40 - running problem

sounds like an electrical problem, the heat seems to be affecting the coil. Try to find a manual and use it to test the ignition system.

Re: jawa 40 - running problem

yeah, i thought that might be te case, i poured cold water on the coil for a bit one time, and it didn't seem to do anything...

my dad has an old lucas 12v coil, will that work on a 6v moped?


Re: jawa 40 - running problem

George Smith /

nah and especially not a jawa, you may have an issue with the ignition coil and or the lighting coil for it, it's possible that someone replace the lighting coil on the coil pack with a headlight one and that will cause exactly what you're talking about, i had a jawa doing exactly that then i opened it up and bang there it was, the coil with the red wire on the retaining ring should be smaller than the rest, if it isnt there's ya prob if it is, may not be a bad idea to replace it... also check your grounds if the only ground you are using is at or on the coil it will also cause this issue.

Re: jawa 40 - running problem

well, i think i fixed it...

i had some crappy spark plug boot i rigged up, and the wires fell out.... anyway, i put a new one on, and now it runs all right...

how should i go about creating a second ground?



Re: jawa 40 - running problem

George Smith /

generally from factory mine have had a ground at coil for coil and horn, and one off of fuel tank but if it's running fine leave it for now :)

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