My new to me 90 FLHTC that I picked up New Years Day was running great. I got it out a couple times for short runs. After checking the oil I decided an oil change was in order.
The oil I drained was thick and black. The oil I replaced it with is Mobil 1 V-Twin oil.
So today I rode up the road a half mile and turned around. On the way back it started backfiring as I rolled throttle in. By keeping the RPM's down I limped it back home and parked it.

It was running fine when I got it. After the oil change it started backfiring. The only other change would have been two gallons of pure gas from a gas can I put in. But I ran it afterwards with no problems.

I'm hoping I find a loose battery cable I may have bumped futzing with the oil tank cover.

I got a three day weekend coming up with some nice weather so I was hoping to get some rides in.

 

Try new gas first.

 

My guess is that the two aren't related (oil change backfire). Make sure you're running the higher octane, fresh gas. I would say that's the likely grimlin. 91 octane is what I run. I have never tried anything less than 89 but, they tell me it will run like crap.

BTW, congrats on the electraglide. You're gonna love it.

 

I think we can say the oil change has nothing to do with any back-firing! That leaves the gas. Ride it until you can fill the tank as much as practical with decent stuff.

 

What did you use to rempve the oil filter?
The crank position sensor can be easily damaged if it is hit by the filter wrench, this will affect ignition timing.

 

On a stock '90 the filter is under the rear of the trans, well away from delicate stuff like crank sensors!

 

Check the wiring,especially under the seat area.Someone in the past may have twisted wires together or cold soldered for an accessory connection and a loose or corroded connection is showing up.

 

Think I would dump the gas and put in new. If it was still doing the same I would check ignition wires, battery cables, coil and spark plug wires

 

Change spark plugs first thing. Going from dino oil to synthetic will clean out the combustion chamber and may have messed up a plug. Also, you will find that synthetic will leak at the base gaskets. I changed to Mobil 1 Vtwin in my 99 and it started seeping, so I changed it back to dino and it has not leaked for the last 20,000 miles. I have 43,000 on it now with no leaks anywhere.

 

exactly my thoughts.