This is an intermittant problem but is occurring more regularly now. Happens when engine is hot and when engine is cold.
96 Harley FXDL, Crane hi 4 single fire ignition, 12.53 volts measured at battery terminals, all electrical connections checked for tightness and cleaned.
Forward and aft cylinder electrical leads from ignition module to coil and plug wires switched - Aft cylinder still did not fire. (Coil good)
Lead wires from module checked, intact, no apparent damage.
Module removed from nose cone, inspected, no apparent damage.
New plugs installed and gapped to manufactures specs. (approx 200 miles on new plugs)
Inline spark tester installed, when cylinder not firing very weak spark noticed, when cylinder started firing very strong spark noted.
I agree with "rselvy". Plugs will foul easily when you modify things and do short "test" starts. had it happen twice to my 2000 custom sporty. Both times the front fired but not the rear...(sometimes backfired though) plugs got carbon fouled real quik.
An expert who has achieved level 2 by getting 100 points
An expert that got 5 achievements.
An expert who has written 50 answers of more than 400 characters.
An expert whose answer got voted for 20 times.
Re: Rear cylinder not firing
The first thing I would do is replace the spark plugs again. You can foul a plug and it will cause you more problems than you can ever imagine. I see you have done all the logical things that I would recommend but I did not see you have replaced the plugs after the 200 miles. You would be surprised at how many times a $2.00 part can cause fits beyond belief.
a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need. goodluck!
- If you need clarification, ask it in the comment box above.
- Better answers use proper spelling and grammar.
- Provide details, support with references or personal experience.
Tell us some more! Your answer needs to include more details to help people.You can't post answers that contain an email address.Please enter a valid email address.The email address entered is already associated to an account.Login to postPlease use English characters only.
Tip: The max point reward for answering a question is 15.
I would check the compression on the engine. It should be about a hundred pounds and there should be no more than 10% difference between the cylinders. The next thing I'd do is check the primarys of the coil. Your bike came with a dual fire ignition system on it from the factory so this means that the ignition system is not stock. This is where I'd be suspicious. The coil will have three terminals on it if it's a single fire coil. Check between the center terminal and the outer terminals. You should have 2-3 ohms resistance from the center terminal to one of the outer terminals. Check center to one terminal, then center to the other terminal. If this checks good, it may be the ignition unit itself. Take the cover off of the timer cavity in the nosecone of your engine and go for a ride. If this cures the problem, then you know this is it, getting hot and misfiring. If it keeps missing, stop by a Radio Shack or an electronics supply house and purchase a small can of "component cooler". Ride the bike until it starts missing and spray a bit of the cooler on the ignition unit. See what happens. It could be a vacuum leak as well. Might be the intake to head gaskets or the intake manifold seal where the carb plugs in if the carb is stock.
The 120° advanced reading may indeed be correct. Here's why. Your bike is equipped with a "dual fire" ignition system which means both spark plugs fire at the same time every time a piston comes to top center. This creates a "wasted spark" as one spark plug is firing on a cylinder that is on the exhaust stroke. Since a Harley engine is a twin cylinder engine that uses only a single crankpin, the pistons are on a cycle that is not exactly 180° apart like in most engines. If I had to take a guess at your problem, I'd say that your fuel air mixture is too lean either due to improper setup or you have a vacuum leak. If your bike is equipped with a carburetor, check to make sure the accelerator pump is working like it should. Take the air filter off so that you can see into the carb. With the engine OFF, crank the throttle to wide open position while watching the brass nozzle just inside the carb opening. It should spray a squirt of fuel into the carb. If it doesn't, you need to replace the diaphragm in the accelerator pump in the float bowl of the carb.
Check the pipe right where they come out of the heads. It depends on what type of exhaust system you have on your Road King. If the stock exhaust is on the bike, the rear cylinder exhaust is directed to both mufflers. With the exhaust from the front and part of the exhaust from the rear cylinders going to the right side muffler, it gets more exhaust than the left side and runs hotter. Like I said, check the temp of the exhaust pipes at the cylinder heads. If one of them is cold, that cylinder is not firing. As long as both of the pipes are hot there, you're fine. Just ride the bike and have fun.
fuel flow to cold pipe cylinder may be stopped with trash or sticky float.Resistor in plug wire for the one not firing could be bad. Try changing coil from one that is firing to the one thats not,see if that pipe gets hot or does the same thing still happen. coil ,plug wire, or fuel would be my primary focus.
Do NOT ride it on only one cylinder. Lots of bad things can happen. Sounds like some kind of electrical problem with the one cylinder. Could be bad plug or plug wire or a loose connection or intermittent short/damaged wire at or near the coil.