Hi all, hope someone can advise. 89 1200 recently had a module go bad so fitted a later one I picked up from a swap meet. Think it’s for am FXR. Tick over is fine but as soon as I open the throttle I get a small back fire through the carb. Seems once warm and hard riding its ok but it does take maybe 10 minutes to stop back firing. My guess is timing as the advance is going to be different between an XLH and an FXR. Is there anything that can be done. Should I advance or retard the timing a notch or two ?
Any advice appreciated.

 

Have you adjusted the idle mixture? You probably should not try to tune unless the engine is completely warm, that's the preferred (and best) method.

I have no idea what timing curves are on the FXR vs. XLH module, maybe someone like aswracing can help out, or ask in the FXR forum.

John

 

Haven’t changed a thing other than change the ignition module. I took I out tonight and it ran like a bag of ****. Pulled the choke and it got better so am now thinking air leak. Sprayed the area with easy start but had no effect. Did a search and seems to be a common issue.

 

Yes, it's a good idea to change the manifold and carb seals if you really want to eliminate any issues. That's a very easy job.

John

 

I check my intake with brake cleaner spray and that little red extended nozzle that comes with it.
I've used WD40 and it works great too.
Start up and get down there where you can see the seals and spray them. If the engine changes then the seals are leaking.
Brake fluid or WD will slow down the engine (what you want). I'm not sure what easy start is. If its starting fluid then I'd not use it.
If you move your timing first make sure you mark it real good where it is now. That way you can go back. You don't want it out of time.
Good luck with it.

 

Just a thought.
If your bike has a VOES switch have you tested it to be working?
VOES is a vacuum operated electric switch. Its probably under the gas tank mounted near the intake manifold, connected with a vacuum hose and 2 wires to a plug-in.
The test is to idle the engine and disconnect the wires. The engine slows down then its working.
If it's not working you might notice it at low speed (open position). idn
Wouldn't hurt to check that out.

 

more thoughts...
Since its running good when you're getting on it then I'd leave the timing be. At least for now.
The VOES (if you got one) doesn't do anything above like 2500. That advance curve is built in the ignition module you put on there.
Between 1500-2500 is where you want the VOES switch deactivated (not connected). If its connected then you probably will get some spark knock.
At idle to about 1500 (the HG set point) you want it working, switch turned on, that tells the module you're not on the throttle very much and advances the timing.

Or something like that anyway. lol

 

All good points. I’ll keep you all up to date. Probably the worst fault you can have as it could be anything .