Spark on one cylinder, tried all I can think of!

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badhabit1

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Aug 5, 2011
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11
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56
Location
Illinois
Been using this website to try and diagnose my problem. Thought I'd post and ask for help. Anyway, I have an 81' Excel 3 340cc. Bought it this summer and it had been sitting for a couple years. Got it home and drained fuel and cleaned the carb. Got it running. Ran really great, would rip across the grass and idled perfect. Anyway, about a month ago it develop a missfire and will only spark on one cylinder, very occasionally will it spark on the flywheel side. Switch wires and it will spark on the other side. On my second CDI and my second coil. Unhooked ignition, kill tether and shut off switch, no help. Double checked all grounds, even adding one from engine to frame. Ohmed everything on the stator, everything ohms good. Even took stator off and gave good general cleaning. Even tried cdi and coil from my brother in laws john deere sled. Fired on both sides, just really weakly. Could'nt rev and barely idled. I'm completely stumped, need some ideas from the experts. I monitor the misfire with clamp that goes around the spark plug wires and gives rpms. Any ideas?
 
If I am not mistaken aren't these sleds based on a "wast spark" system that is supposed to spark both plugs at the same time? Did you ever replace the wires. If you switched wires and the side with spark switched that tells me that the spark plug wire is your problem. I'll bet the good wire is getting the spark to the spark plug but then the electricity is returning through the other wires shielding instead of through the spark plug.
 
Yes, waste spark system. I've ohmed the wires and coil, all checks good. Gonna try a new wires anyway though. I think I've tried everything else! lol.
 
They may ohm out well but that is not the problem, the problem is weak shielding that is letting the electricity through the shielding instead of reaching the plug.
 
You have thousands of volts being delivered through a 5000ohm resistive plug cap. If there is a nick in your wire to ground (Aluminum/metal), it will take that path and not deliver the voltage to your plug. Shielding is the wrong term. There is no semiconductive layer in a spark plug wire. It is simply a low count, course strand unshielded conductor with no mechanical protection.
A high voltage shielded conductor would be nice, but you would need a technical consultant every time you changed a plug cap.
 
I got ya, basically the coil is producing good voltage but all the voltage is jumping down one wire only. Will try new wires tomorrow. Any other ideas anyone?
 
The plug boot (cap) is high resistance to limit current and not over duty your stator. If your plug cap is below a 2000ohms or so. it will tax your stator and not deliver the voltage required for proper ignition. There are spark testers out there (more common in the outboard world), that measure spark jump. That may be a viable test if you suspect a bad cap or wire. The easy solution at this point, (being that you already changed a bunch of stuff), would be to change the plug boot and wire to eliminate.
Hope this helps!
 
So using some left over plug boots from my ol' 5.0 mustang would be bad. They have almost no resistance at all. Need to ohms the plug ends today.
 
Pulled the plug boots and ohmed them. Got about 5.5k on each cap. Still need to install new wires yet. Got some 8mm silicone jacket, stranded moroso spark plug wire laying around, should work right? It just has a plain wire core, like the stock wire.
 
Another possibility.

The cooling shrouds are plastic on those ET's and the head gasket is fiber. The only ground for the head to the system is the nuts that hold it down. Corrosion between the nuts/studs/head could cause what you are describing. Electricity will go to the least resistive point which could be your PTO cylinder leaving the mag side wanting. Try a jumper wire from the cooling fins on the problem side to ground and see if things change.

Good Luck, opsled
 
Well, plugs aren't "brand new" but I have about a half dozen laying around. Tried various plugs. Gonna try grounding the cylinder head, as mentioned, tomorrow. Try new wires too. Will put a couple clean plugs in for the heck of it too.
 
had the same problem with my 80 enticer 340cc everything would test good every time i would test it. till one day i change the ignition coil with a after market one. ran good for a couple of weeks and started to do it again. so i changed it again with the same thing happening. Got to the point that i just told my self F#@@# am pick up a new yamaha coil. it bin a couple of years now and it still running good. Am not saying that could be your problem just saying what it maybe
 
marc8_2 said:
had the same problem with my 80 enticer 340cc everything would test good every time i would test it. till one day i change the ignition coil with a after market one. ran good for a couple of weeks and started to do it again. so i changed it again with the same thing happening. Got to the point that i just told my self F#@@# am pick up a new yamaha coil. it bin a couple of years now and it still running good. Am not saying that could be your problem just saying what it maybe
Click to expand...
Another interesting idea here, and I appreciated everyone's ideas. After all the testing I've tried, I'm ready to hear any ideas! It does appear that my current coil is an aftermarket one as it has no brand name markings.
 
badhabit1 said:
Another interesting idea here, and I appreciated everyone's ideas. After all the testing I've tried, I'm ready to hear any ideas! It does appear that my current coil is an aftermarket one as it has no brand name markings.
Click to expand...

If everything test good and you try everything i would try a yamaha coil. hope it work for to as it did with mine. good luck and lets us know
 
Put my digital volt meter on the leads that go to the coil. Orange and black wires. Just curious as to the output. Never got above 1volt. Actually never any higher than about .7 of a volt, pulling the recoil as fast as I could. Just wondering if this is good, bad, thoughts?
 
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