Question about Harley Davidson FXDL Dyna Low Rider Motorcycles

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I have a 1990 fxr with a single fire ignition, cam and s&s carb. I am not getting the rear cylinder to fire. I just cahnged the coil but no change. I have compression out the exhaust pipe for the rear cylinder. I have also swapped he plugs and wires but no luck.

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With a single fire ignition, you cannot swap the wires. A dual fire ignition, yes, but not a single fire. You need two things to get the cylinders to fire, spark and compression. Take the plugs out of both cylinders. Run a compression test on the rear cylinder. You need at least 100 PSI to get the cylinder to fire like it should.

Next, put your plugs in the wires, (they should already be in the wiresand grounded) and spin the engine over. Watch for the plugs to spark,especially the rear plug. If you have spark and compression it should run on the rear cylinder. If it still doesn't run, either something is way wrong with the ignition or a very bad air leak on the intake.

If you don't have spark at the rear plug, you need to check the coil. A single fire coil is different from a dual fire coil. The primary wiring is different as well. If you've got the primary wired incorrectly, you won't get spark at the rear plug. Go to the website of the manufacturer of your ignition system. Most of them have downloadable installation instructions. Check your primary wiring.

Posted on Oct 03, 2009

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