Weak Spark

Brand new plug...Just finished cleaning the points (which weren't even that dirty)... So now I need to replace either the condenser or the coil...Right? Is there a way to test the condenser or the coil? I'd rather do a test first to make sure that is the problem...is there anything else that could be causing a weak spark? I've allready replaced the spark plug cap and wire

Re: Weak Spark

Its possible that the magneto magnets are worn and the gap has increased weakening the spark, check for cracks around the top of the coil (this is best done in the dark by cranking an engine and see if it is sparking or arc- ing(I found this out the hard way) to one of the coil wires) this can also be fixed with silicone gasket sealer but it is not a permanent soulution, the condenser is a trickier problem but it should be cheap enough to replace anyway,,, just a few ideas

Re: Weak Spark

It's also possible your flywheel key's out of place.Chuckle inserted !Don't start on me Ron.I learned my lesson! SEE! I'm passin' it on so some other poor fellow doesn't get hisself dope slapped into oblivion! GEEEEZ !! (;>)

Re: Weak Spark

Ron Brown /

Vespa,

Here are some words from a previous post.

This is a coil test:

From the plug wire to ground, you should read several K-ohms, maybe 5 - 15 K-ohms. From the points connection to ground you should read between 0.5 and 1.5 ohms.

To test the coil, connect a spark plug from the plug wire to coil ground, connect an ignition condensor (any will do for this test) between the points terminal and coil ground. Connect the negative of a 6V battery to coil ground and touch the points terminal momentarily with the positive lead. This should give you a spark at the plug.

If you have a vom, check the ignition components as follows:

Disconect the wires from the points. One of these wires goes to the magneto ignition power coil. You should read a low resistance to ground on this wire, 1-2 ohms.

Another wire goes to the condensor, read this to ground on RXMAX, that is your highest resistance range, the needle should kick, then settle down to infinity. Reverse the vom leads, same thing should happen.

Another wire goes to the ignition coil primary, this connection is also connected to the kill switch. Disconnect the kill switch wire only from the ignition coil, the wire to the coil should read 1-2 ohms to ground.

From the wire to the kill switch, to ground, you should read infinity with the switch in "run" and 0 ohms with the switch in "stop".

Connect the vom from ground to the wire terminal on the points and make sure they are 0 ohms when closed and infinity when open. This seems dumb, but sometimes points that look clean do not connect.

Re-attach all of the wires to the points. Disconnect the wire from the points at the ignition coil. Measure this with the vom, it should read near 0 ohms. If your meter is sensitive enough, you should see a slight deflection of the pointer as the points open and close.

With the vom still attached and set to about 12v DC range, spin the motor by hand. You should see some deflection of the meter needle.

Pull your plug (spark, that is) and make sure the piston is at or very near the top of it's stroke when the points open.

Re-connect the coil wire. Measure from the plug cap to ground, you should read 5-15k ohms. If this is infinity, unscrew the plug cap from the wire and read through it. This should be 5-15k ohms, if it is open, replace it, if greater than 15k ohms, it may still work, but replace it with a paper clip for test starting then re-install it after you get the ped running.

Read from the end of the plug wire to ground through the coil, you should see 1-5k ohms. If this is infinity, the coil is bad.

Lastly, using the ohmsX1 scale, verify that all of the grounds really are.

None of these tests are guaranteed to indicate a problem, especially where you read coil resistances and they seem ok. Substitution is the best test here.

Hope this helps,

Ron

Re: Cheap and Easy

As a rule, I always clean off any rust on the flywheel magnets and coils inside the magneto with one of those green pot scrubbers and WD40.

Rust on these items can scramble the magnetic field.

Jim

Re: Cheap and Easy

Thanks for the tips everyone, it will probably take me a few days but I'll let you all know when I get it figured out.

Re: Weak Spark

Jon Dalton /

Someone explained to me once that when ignition points get old, the sparking that goes on between them and the repeated contact will increase the carbon content of the steel and cause them to lose conductivity, so your points could look just fine but really be no good. I would get new points for it first, if they are available. I've had this experience with an engine before where I cleaned the points really good and still it had no spark at all, and I got new points and then right away it made a perfect spark. Also, with my Honda moped the spark was very unreliable, leading to a lot of breakdowns and cleaning the points would only help a little, and after I put new points in it i had no more problems with spark. My friend's honda moped, same deal.

Re: Weak Spark

Ron Brown /

Jon,

What you describe is true and I have heard it is worse for Honda points than others, supposedly because the points are plated and are no good once the plating wears off.

I have to say that I have never had this problem. I have had to clean the points several times before they worked correctly, but a vom has allways kept me straight by showing resistance when the points are closed.

Ron

« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account