Ignition question (updated)

[GWGAllisfan 159]

Will an automotive timing light work on small engines like a 243000 series briggs? I've got on that won't start. It has compression, and plenty of fuel, but not flooded. Though the carb was the problem, so changed to a known good one. From holding the plug wire on the block I have spark. Holding the plug to the block I have spark. Touching it with the left hand I surely have spark![:0] I just thought I would check with the timing light, so I hooked it up and it didn't light except at irregular intervals. I took the wire off the plug and the light lit about like it should. I then pulled the plug and set it on the block and the same thing happened. Cranking speed seems high enough with the plug in, by the way. Does this mean: The plug is bad? It has only about 30 minute of run time on it. Or do I have too little ignition voltage to fire under compression? If that's it would a new condenser help, or is it replace the coil time? Any ideas/opinions?

[BLT 717]

Timing light won't help you as you don't have any reference points to shine it on. If you can get an eighth inch spark or better the plug should do well under compression as that is four times the normal plug gap.

[ReedS 5]

I think that I would try the new plug thing first, it won't hurt anything and if it doesn't change things you'll have a spare for some other time. I've seen bad ones right out the box. Make sure your plug, new or used is properly gapped as well. As far as the timing light Q goes I believe that and 12v inductive (clamp on plug wire) style timing light will indicate that the coil is indeed firing but as far as indicating proper timing is concerned the problem would the lack of timing marks that would mean anything. The marks that do exist on the flywheel where meant only for static timing (engine not running) if haven't lost my marbles. Back the ignition question if the plug doesn't solve your problem then it would be time to turn your attention to the points and condensor making sure that there is nothing shorting the pionts out ie: kill switch and it's wires, loose screws etc, as well as mkaing sure that the point gap is set properly to .020 and that they are clean and not pitted. As far as the coil goes if it hurts when you are holding the plug wire chances are good that it is ok. I have had some engines that'd run just fine with an orange spark but what you really want to see is a bright blue spark that's present every time the points open and close. Good luck!

[GWGAllisfan 159]

Thanks I was hoping I had found the problem, but it appears that it lights the light less often under compression is meaningless... It just doesn't make sense. It has fuel, it has compression, but doesn't run.

[D-17_Dave 12]

There is a mark on the Briggs. It's on the flywheel on the side of the aluminium finns faceing forward. It's an arrow pointing to the magneto. You'll have to run it with the shroud off to see it. I think you have low ign. voltage. It shouls jump across 1/3" good w/ a blue spark. Yellow spark or irregular spark patterns won't fire the plug under load. I'd try a plug first, but double check you magnet for a clean surface. Likewise with the magneto surface and the air gape. Then regape and clean the points. Weak or dirty points might still fire but clean points will always fire hotter.

[Bear 47]

You may want to do a leak down test to be sure valves are seating.Have you tryed carb spray or gas in plug hole. If no poping I would check valves.

[GWGAllisfan 159]

I went to the local Ace and bought a new J8C plug. After a few seconds it caught and fired and ran. For the first few minutes it black smoked and quit after a minute or so, but would start right back. After a few minutes it settled down enough to adjust on it some and it is running at every thing from slow idle to top speed. I do think you are right, Dave, the spark is weak. After it had run for about 30 minutes, I though I'd see if it would start again with the old plug. Results: Older plug (j8c) Wouldn't run Back to ACE plug: Ran Tried an RJ19LM: Won't run Back to ACE plug: Ran I think it has marginal spark voltage. By the way the older plug had only 15 minutes run time. would never believe it if I hadn't seen it. Thanks for all the advice.:)

[tec2484 1]

I'm with Dave, Check the magnet for rust and check the gap on the magneto.

[ZippoVarga 61]

I've had experience with fouling out plugs if i didnt run the engine long enough to get it up to temp before shutting it down. Also it sounds as though the carb may have been out of adjustment with the black smoke you referenced along with having to make adjustments to get it to idle and rev with out hesitation. This too could have caused your original plug to foul out prematurely. What color was the original plug's end? If it was any other color but a light cigar color then your either preigniting the spark plug, running too rich a mixture or too lean causing a blackened plug end...I think I got that right. At any rate, just sounds to me like a bad plug from a mal-adjusted carb. But, I tend to think on the simple side of a problem before the complicated end. Sean aka Zippo

[B.Ikard 2]

Randy, Are you off Monday? I might be able to pay you a visit and we can put our heads together on this problem.... The timing light can be used with an auxilary 12V battery and the shroud removed-there is an arrow on the flywheel and another on the coil mounting bracket-it is all spelled out in the older briggs manual (brown cover) I marked one of my 16's flywhel, made a pointer, and drilled a hole in the shroud so I could time like a Kohler. I used a dial indicator to find & mark TDC on flywheel....then timed per briggs manual with the before mentioned arrows for a firing mark of reference. I filed a groove in the flywheel for both marks and hit with a little white paint. Sometimes I like to split hairs I guess :) Brent

[GWGAllisfan 159]

It seems to be running OK now. I ran it for about half an hour at everything from slow idle to full throttle and it runs about like it should. It's weird that the plug made that much difference, isn't it? Thanks for the offer Brent, but I don't get President's day off, so I will have go to work Monday.

[ZippoVarga 61]

Like I mentioned in my earlier post, a fouled plug will stop the charge from the coil dead in it's tracks. I have one of the handiest little contraptions ever devised. And it's saved me numerous trips over the years to purchase a new plug. It's a spark plug cleaner that is like a tiny little sand blaster. Glad all is well with your tractor now. Sean aka Zippo