Running on one cylinder

[StrawBerry]

Hey y'all!

I've got a problem with my 1990 FXR.

It starts up just fine, and runs great for about a mile, and then the front cylinder stops firing. If I shut it off and try to restart, it still doesn't fire; but if I leave it for a while itl run fine again. The exhast will smell like unburnt fuel.

A little about the bike-
Its a '90 FXR with a Zipper 80/80 kit. Spyke single fire coil, Zipper thunderbolt ignition, thunderheader 2-1, 40 3-phase charging system. (previous owner toured with a trailer), and wayyy too much chrome.

I ran a line from my positive terminal to the positive posts on the coil, to test for shorts. Still no good.
I replaced the coil. Still no good.

I pulled the plugs and ran it, and it sparks to ground just fine.

Do any of you have any idea what this might be? I'm mechanically inclined, but inexperienced.
My only other thought is something causing the exhast valve not to seal?

Thanks guys!

[TriNortchopz]

Sounds like a bad spark plug. Did you change them? Even just try swapping them - front to back. A plug may not fire properly under compression when it sparks okay testing it out of the engine. Try swapping plug wires next...But do just one change at a time so you can rule out what is not the problem.

Links to components listed for reference:

Zipper's 80/80 Evolution® Big Twin Kit: http://www.zippersperformance.com/zi...-kit-carb.html

Spyke® Coils:

http://www.zippersperformance.com/spyke-coils.html

Zipper's Thunderbolt Nosecone Ignition:

http://www.zippersperformance.com/zippers-thunderbolt-nosecone-ignition.html

[BadMonkeyMW]

As mentioned, replace that front plug right out of the gate. You could also have a plug wire breaking down after it heats up a bit, so try swapping front to rear and see if the problem migrates with it. Assuming you have the stock FXR coil mount setup, the plug wires are the same length.

[StrawBerry]

Fresh plugs. Same problem. Swapped wires. Same problem. Replaced ignition coil. Same problem.

Anything else I should try before I order a new thunderbolt?

[TriNortchopz]

Fresh plugs. Same problem. Swapped wires. Same problem. Replaced ignition coil. Same problem.

Anything else I should try before I order a new thunderbolt?

Any chance the switches for the Thunderbolt got changed:
"The Thunderbolt nosecone internal ignition is designed to fit all Evolution® Big Twin and Sportster® models, as well as ‘70-up Shovelhead and ‘71-up Iron XL’s. It is fully contained within the cam cover, replacing the externally mounted module on all models originally equipped with electronic ignitions. It features external switches that control single or dual fire operation, multi-spark function, advance curve selection and RPM limit."

What about checking it with a laptop: "The Thunderbolt is also programmable with a laptop or standard PC. Software and an interface cable are required for connection between the tach port and the computer USB port (purchase separately)"

See what this guy found on his '88 FXR: "UPDATE: Turned out to be the ignition module. The bolt that holds the timing cup on came loose and wiped out one of the sensors on the back of the IM. New cup, LOCTITE on the screw (!) and a Dyna2000i ignition and she runs great..." https://www.reddit.com/r/Harley/comm...er_not_firing/

[Guest]

Fit Point's & an Advance/Retard unit and ride it,.... ya cant beat points

[StrawBerry]

I'll check the timing cup bolt and get me some points and update. Might be a while because of life things.

[Tattooo]

Fit Point's & an Advance/Retard unit and ride it,.... ya cant beat points

You got that shit right... Runs better cranks much better especially with a kick bike...

[TriNortchopz]

Fit Point's & an Advance/Retard unit and ride it,.... ya cant beat points

Yup, simple is good, no battery (or laptop) required. Been sparking plugs since 1910, thanks to Charles Kettering:
"The first reliable battery operated ignition was developed by the Dayton Engineering Laboratories Co. (Delco) and introduced in the 1910 Cadillac. This ignition was developed by Charles Kettering and was a wonder in its day. It consisted of a single coil, points (the switch), a capacitor and a distributor set up to allocate the spark from the ignition coil timed to the correct cylinder."

https://ipfs.io/ipfs/QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco/wiki/Ignition_system.html

[Dragstews]

1910 Cadillac Model 30 ran a dual ignition consisted of a new Delco four coil system and low tension magneto.

Did a little "Fact Check"

[47str8leg]

I've been running on one cylinder my whole life...

[TriNortchopz]

I've been running on one cylinder my whole life...

Well, my crank's bent, head's warped and when the timing is off, often backfire out the intake...