sparking problem

Jon Dalton /

Apr 15, 2001 04:03PM

ok this is happening again after the moped worked fine for a day, I was on my way to toronto, about 30 miles away from my house when all of a sudden the engine crapped out and started backfiring and jerking and losing speed. I thought it was as if the timing suddenly got retarded so I played around with the timing and got it to run again. Further down the road it screwed up again though, so I played around with the timing again. It broke again and kept doing that until eventually it would take 20 minutes to get it running and then only go half a mile before breaking again. So then I took out the spark plug and it was sparking fine, but after fiddling with the points it would not spark at all, and nothing i could do would make it spark again. So I started pedaling. After pedalling for a long time I stopped and tried to fix it again, this time something I did, I don't know what, made it spark again, but the spark was not great. It ran really bad for a while then quit again, presumably lost spark, so i pedalled the rest of the way, finally reaching my destination more than 6 hours after I left. I can't figure this out. The points are filed shiny clean and i just put a new condenser on. I'm suspicious the new condenser is doing nothing, as what it's doing now is similar to what it did when the condenser wasn't hooked up. It would seem like a loose wire but i don't think there is a loose wire anywhere.

Re: sparking problem

Chris Robertson /

Apr 15, 2001 06:20PM

You just perfectly described what happens when a spark plug gets fouled and needs to be changed.

Re: sparking problem

Jon Dalton /

Apr 15, 2001 07:14PM

it did indeed have a fouled-looking spark plug, but it was the same with a brand new one.

Re: sparking problem

Miguel /

Apr 15, 2001 08:16PM

your new plug is probably fouled now, too. check it. you're probably running too rich or lean or something like that. what's your oil/gasoline mix ratio? check some other things, too.

use fred's guide to troubleshoot. no sense ruining good spark plugs. and use a bosch platinum.

Re: sparking problem

Jon Dalton /

Apr 15, 2001 11:37PM

I put a brand new spark plug in and it behaved exactly the same as the old one, even before it was in the engine at all, i.e. every time I checked the spark I checked with the spark plug in there (new) and another one that had never been in the engine. I have several new spark plugs. My friend just told me it could be the coil, which shorts out when it gets really old, and the resistance in it changes with heat as the insulation breaks down. That's what he said anyways, and it would explain how it takes forever to get the engine running (tbe coil eventually cools down enough to work) and it only runs for 1/2 mile and then gets messed up again (coil gets hot and shorts out) I hope that's it, then I can find a coil and make it fit, I know internet sites that have a universal coil

Re: sparking problem

Chris Robertson /

Apr 16, 2001 12:21AM

What kind of moped are you driving?

You're right. It sounds like the plug isn't the problem. Unless your flywheel or points are loose, I don't think the problem is timing, but it does seem like the ignition is what ails you.

I'll assume that the gas in your ped is newish and there isn't any water in your tank or carburetor bowl.

You could indeed be dealing with a bad coil or condensor. I'd be wary about buying a "universal" coil, though, as I've never heard of these and high tension coils are very precisely engineered for the engines they go into. Contrary to what some people may tell you, there is no easy way to test either the coil or the condensor without plugging them into an identical moped that works (and seeing if it stops working). Forget about testing resistance or conductivity! A bad coil can still appear good with these tests.

Look for loose wires or a faulty kill switch.

Have you tested your engine compression? It's possible that you have a heat-related compression loss. Try measuring the compression with a cold, and then hot engine to see if there is a difference.

Chris.

Re: sparking problem

Jon Dalton /

Apr 16, 2001 04:40AM

The compression is good, surprisingly good for the age of the engine. New rings made a difference, I just replaced them because I broke one of them and didn't want to shell out for a piston. I can tell the compression is good because of the effort it takes to pedal. It is the same hot or cold. The problems on this moped so far have never been gas, only spark. It's pretty obvious that the ignition is erratic when I test with a brand new plug and it gives a weak spark, perfect spark or no spark at all and I never know why. I'm just going to try to replace ignition parts one by one until I fix it. A loose flywheel might have to do with it. I did tighten that nut pretty hard though, just the pin inside isn't perfectly stiff anymore.

Re: sparking problem

Ron Brown /

Apr 16, 2001 11:35AM

Jon,

If you can find it, romove the wire from the kill switch to the points, just in case it is shorting to ground somewhere. If you have an ignition switch that connects power to the ignition, bypass that as well. Look for any wires/connections which may be marginal and fix or bypass them.

Buy a can of circuit cooler from Radio Shack and when the ped dies, spray the coil or the condensor with circuit cooler and see if that fixes it faster than normal cooling. You can also do the reverse and heat components with a hair drier to see if you can make them fail.

Ron

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