Do I need a new ignition coil?

Question

My problem:
Bike runs great for first 20 minutes until it gets hot. When it's hot it sputters and backfires at around 4000 rpm. I have tested my ignition coil and it tested ok, but I have read that they can fail when they get hot. Can I replace it with one off of any 125? The plugs look good, no signs of overheating. Cleaned carbs, compression is good. Bike is 78 KawasakiKE125 enduro

Answer 1

Best thing to do probably is to pick up a used coil from a bone yard and see if that fixes it. I've had problems before like this with trash in the carb jets, but that would usually happen all the time, not just when the bike is hot.

Make sure you are not getting a presurrized fuel tank and starving for fuel - pop the gas cap and see if it helps.

Answer 2

It can be the coil, lead or plug itself although am assuming you would have checked these out. Points and condenser can also give you this problem and even if the points look ok the spring steel can lose tension and bounce.. Some other things to check especially if it's a two stroke is buildup of oil and other contaminates in the exhaust, if it's never been cleaned you can soak it in a solvent (kerosene is probably the cheapest) for a few days and then either a waterblaster or hose to clean it out and leave it out in the sun to evaporate the water. Check the wires and connectors, I know it sounds wierd but I had one that would start and run great but would do a similar thing initially when i hit bumps and ended up as soon as I sat on it the engine died. Took a while but tracked it down to the chain shorting the wires that passed through there when the suspension was compressed. Other parts again if it's a two stroke is the reed valves in the manifold between the carby and the barrel, or the rubber manifolds themselves. Seals on the crankshaft are crucial on a two stroke may leak when hot. And if it's cdi possably the unit itself. Most ignition coils are similar just check on the voltage (6 or 12). Good luck. Hope this helps,

Answer 3

30 year old bike...how many miles on it? Its true, the coil can test ok, then fail when it gets hot but with a bike that old there are numerous things that could be wrong. I would think that the coil is pretty inexpensive, buy one (for the KE 125) and see if that cures the problem. Those things were pretty indestructible, they built them forever it seemed. You can probably find some parts on ebay motors real cheap.

Answer 4

It could be the coil - CDI - pick up coil (on the engine).
Test the coil when the bike craps out - you might not be getting a proper reading with the coil cooled down.

Answer 5

Doubtfully it is an electrical problem, unless you have an electrical choke. This happens to my Jeep Cherokee sometimes. It is the choke valve on the jeep. I assume your bike is carbureted since bikes dont do emission tests. My gsxr is F.i. anyways, it is a carburetor problem.