dead cylinder

Energy One
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sodak68

Member
Took my bike for a ride the other day and it ran great. Got home put it in neutral and laid it on the kickstand and right then it started running bad so I shut it down and started investigating. I found the plug wires were rubbing on the coil bracket and worn through the insulation on the back cylinder which I determined was not firing. I checked the spark by pulling the plugs and turning it over with them against the head and I have spark. I replaced the wires with twisted wires and new ngk plugs but the rear cylinder is still dead and it kinda looked like it was blowing back through the carb a bit. Could it be a bad ignition module? Any thoughts? ? Thanks
 
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sodak68

Member
Well when I tested it there was spark at the plug but when running the pipe is cold and it obviously sounds like it's on one cylinder. Maybe the coil went out?
 
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Sven

Well-Known Member
Shove a rubber handle [so you don't get shocked] screwdriver, up the plug cap, take the shaft of the driver and get it close to the spark plug in question. The spark should jump from the shaft to spark plug go an tap the starter.

No spark it's the other coil.
No spark and it's only one coil, then the wire is broken on the outside or poorly connected. Why? Because the single coil is really one wire in and one wire out. Can't be one spark works and the other does not?

Has spark... Then check compression on both cylinders and report.
 
Th3InfamousI

Th3InfamousI

Administrator
Staff member
Sven said:
Has spark... Then check compression on both cylinders and report.
Click to expand...

Said he had spark so can't be a bad coil. Check the compression if you had spark to the rear cylinder.

If you got the twisted plugs, I know on mine they pop off at the coil occasionally has happened to me twice now while riding and it obviously goes down to one cylinder and it's a bitch to get back on without pulling the coil cover off!
 
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sodak68

Member
This happend before I changed plug wires and didn't change after I switched them. Yes I had spark but thought maybe it was just too weak? I'll check compression when I can. I guess I thought if it was mechanical I'd hear some horrible noise?
 
KaptinAmerika

KaptinAmerika

Guru
Not necessarily.
I have an 03 chopper sitting in my shop right now with an Ultima 120 motor in it.
Customer said one second he is riding along happy and the next he is sitting on the side of the road. No noise just a sudden decrease in power and running super rough.
When he brought it in I fired it up and sure enough a dead rear cylinder.
I pulled the rear plug, it had spark. I looked through the plug hole and could see the valves opening and closing. I put the compression tester on the rear cylinder and 0 compression.
Pull the tank, pull the rocker cover and there is the problem. A deformed beehive intake valve spring that isn't pulling the intake valve closed completely.
 
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sodak68

Member
Well I did a a finger compression check and i'ts very obvious that the rear cylinder as very little compression so I'm going to pull the tanks and rocker cover this weekend if I have time. I'm in the middle of a car build and dont need the expense right now lol. any offers? lol
 
john sachs

john sachs

Well-Known Member
If the motor still has TP rocker boxes, and some mileage, it's probably a worn or broken exhaust guide causing the valve not seating. Some don't think they have a problem with the TP/SS combo until the shit hits the fan. :bang:
John
 

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sodak68

Member
I would sell this bike for 7,000$ as it sits now.Including pillion seat, spare fender struts, sissy bar with back rest and winshield.
 
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