Runs on One But Not the Other

[90FXRS]

A stock engine.....has an aftermarket revtech ignition, accell coil, new top end, compression is 2lbs difference, new plugs and wires.....will run when one plug wire is disconnected but not when the other? The one that will not run seems to suck back into the exhaust from time to time when both wires are connected. Also has new s&s lifters and pushrods......set at 4 turns. The ignition and coil are same as before the top end rebuild. It is an 87 XLH 1100. This bike will be the death of me.......or she, the owner, will.

I forgot something. When the plug wire on the rear cylinder, the one in question, is disconnected there is a difference in the engine. The front cylinder keeps hitting and running. When trying to run on just the rear......it dies

 

[NCBILL]

Possible weak coil? Bench test it for results.

 

[HDDon]

Does the Rev Tech ign. have any external adjusters? Can the Rev. Tech be set up for single or duel fire?

 

[tourbox]

Sounds as though you are running on just the front cylinder only. The rear pipe is or should be colder than the front. Reverse your plug wires in the coil & plugs. Take the front wire off the plug and coil then place it to rear plug and rear section of the coil. Do the same with your plugs. You can check to see if they,the spark plugs, fire by taking both out and ground them to the heads and crank it over. They should both fire.Unlike newer model with ION sensing. If the trouble follows the plug wires then it is a bad plug wire. If one plug fires grounded and the other doesn't then reverse the plugs in the wires. If good plug doesn't fire on other wire then plug wire or coil is bad. If good plugs fire on other wire then other plug defective.
tourbox

 

[90FXRS]

Thanks for the response and here is an update. I never thought about feeling the rear pipe. I did swap the plug wires at the coil to see if one side of the secondary was defective, no change. Pull the front wire and it dies. I know Sportsters are a different breed but I would figure it should run on both or either cylinder. I don't know the history of the bike. Is it possible for the cam gears to be off by a tooth if someone has been inside the right side? Also, the ignition is a new Dynatek 2000i-1P. Coil resistances are 2.9 on the primary and 11.8k on the secondary.

 

[joel]

Here is a thought.
Have you confirmed proper charge rate?
Maybe low charge rate can affect coil output.
Use a spare spark plug installed onto the rear cylinder wire, ground it to the head, start the engine and monitor the plug for spark from idle up to 1500 or more to see if and when spark begins to show on the plug.

 

[tourbox]

Did you change from the Rev Tech ign. to the Dyna? Did it run right before the top end?
Yes you could be off a tooth if some went into te gear cover side.
tourbox

 

[dolt]

2psi difference in compression from on cylinder to the other would indicate that the cam gears are in time. Problem sounds electrical to me.