KymcoForum.com

I skimmed over the past posts here so may have missed it.


Did you check your ground connection to the engine block? The engine block provides ground for your spark plugs. I've read many posts on other forums about a corroded ground connection causing strange electrical issues including no spark or low spark voltage/current. I've read this for cars as well and actually fixed one of mine by using a wire brush and cleaner on the ground connection and bolt.


Just a thought. Like I said, I may have missed it if already thought of.

Just realized you already indicated when it ran it ran flawlessly so that SHOULD get the injector off the list.
You also said something about the plug would spark when out but not when in. How did you know it did notbspark when in? Straighten me out on that one, please...

I think I have read about all the forums on this subject, and pretty much checked them all off, and I am still stuck.  My problem is a no spark issue.  I have a spark checker that I have used on small engines for years, if the spark will jump the gap, it will fire under compression.  With the plug out, I have good spark, plug in,  no spark. These are some of the things I have done with basically no change in the problem.  I had bought a new battery when I got the scoot before I knew about this problem.  Once I got into it, and reading all the blogs about batteries, I bought another one with the CCA of 175, the same as what came with it.  I fought with the theory of possibly starving the ECU while cranking with the plug in.  Voltmeter proved that wrong, but still I used another battery to power everything but the starter, no change. Okay, so it is not voltage drop, it does crank slower with the plug installed, so could it be the signal from the pickup/pulsar/crank position sensor.  It ohmed out correctly and I really hated to do it, but pulled off the crankcase end to get to it.  It was melted pretty badly.  Oh boy, thought I had it, replaced the coil , checked the gap, running about .015, perfect, buttoned her back up, no change.  I have ohmed out the ECU and connector to the manual, everything checks, removed and replaced all ground wires and have used dielectric grease on everything. Checking the output from the pulsar coil, it is showing about .45 volts AC cranking without the plug installed and maybe .42 with it in, not enough to make a difference one would think.  I am showing over 12 volts going to the hot side of the coil as well as the power to the ECU while cranking.  The only code she is throwing right now, is the O2 sensor because the exhaust is still off from changing the pulsar.  I keep thinking it is something stupid and when I find it, she will purr like a kitten, because I have about left no stone unturned, including valves.  I have checked continuity from the ECU to the signal side of the coil along with about every wire in the harness.  I am starting to look real hard at the ECU but everything says it is okay, it performs the precheck perfectly, throws a code when it should, but what else is there. I have cranked it long enough on a couple occasion that it has started, once running, it runs perfect.  You can tell when she is going to start as the tach starts to jump. Any and all suggestions will be truly appreciated.


Crud, I haven't gained a thing.  I have now another ECU and I have replaced the stator and pickup coil.  I have wrung out every wire, powered the ECU separately from the starter, checked all grounds, and still, using a spark checker, have spark with the plug out, no spark with the plug in.  Plug is not hooked up,  using the spark checker is both cases, plug just fills the hole like a plug and raises compression.  Engine turns over a little slower under compression, but still quick enough.  Have jumped it with a car battery.  Have two new coils, two ECUs, new pulser and stator, and I am right where I was a year ago.  I assume it is the ECUs job to determine which of the flywheel tabs trigger the coil.  I assume the square tabs, might be 6 of them are for the injectors and possibly timing advance, where the big rectangle one is for ignition.  I just can't see that much of a change between cranking with the plug in or out, only a small difference in the strength of the signal generated by the pulser coil.  Hate to drop another $372 for another ECU, if any of you guys have the hood off your 300 and wouldn't mind plugging in a couple of ECU to see if they are any good, I'll gladly pay shipping both ways.  Thanks!

Sorry to see there is no progress.
Yes, why not trying to bypass your ECU with an external CDI-box. Would be interesting whether it works. Pls keep us posted about any outcome whatever.

Welcome and you seemed to have done EVERYTHING that can be harped on in a situation like this! I think Ruffus is on to something simple like a faulty plug wire or cap except for it runs great once it starts! The normal for this and the People GTi300 with the same engine is two revolutions on the starter and it runs.

Sounds like the only thing left is to plug in a "known to be good" ECU to at least rule out that possibility. The only problem with that is NO ONE just happens to have any of those laying about!

Have you tried a new plug yet? Or did I miss that?

Oh, I have tried a half dozen different plugs, finally ended up with the nine dollar titanium plug that the electrode comes to a point. Nothing.  I wish I knew someone who had a 300 with easy access to the ECU .  I certainly would pay shipping both ways to have someone plug this thing in and either thumbs up or thumbs down it.

@JaydeeFL,
I know it sounds strange, but try to take a new spark plug and put a simple short piece of stiff blank electrical cable from your ignition cable (sparkplug cap taken off) onto your sparkplug. Try to start. Check this blank cable piece is not touching anything.