So I got a chance to get my paws on a 76 sportster bicentennial edition. This will be my first Harley, was a car mech for 7 years, before changing carers, and have a good knowledge of mechanical stuff, but never worked on a Harley, I've been a sport-bike rider since I was 16, and dirt-bikes before that, basically Ive had a motorcycle since I was about 8 years old... the current owner, my uncle, said the bike has an issue with backfiring. He said he would be riding, the bike, and it would start backfiring severely. He said he thinks it is in the wiring somewhere, and that he stops the bike, wiggles the wiring harness around, and the symptoms stop. anyway, so I'm thinking about driving it back home from Illinois to Florida, and wanted to know if anyone has had this problem, or suggestions about where to look. common pinch points etc... dont want to get stuck out in the backwoods of Alabama...
thanks for the help in advanced, and thanks for putting together such a nice board, I'm sure I will be using it a lot!
Noah

 

Well,You sure have found the right place to get answers! Sounds like You've got a chance at a rare bird,that bike,hope Ya buy it! Folks like Pinion Gear,Ironmick,and everyone else will help you out I'm sure..Getting another Iron back on the road makes everyone here happy from what I can tell from a year or so of reading.Good luck with it!

 

Not sure an electrical problem is what is going on there but you would be looking for common pinch points in the ignition system wiring. You have a coil wire that runs from the kill switch and a wire that runs from the same switch to the key switch (wire runs under the tank) as well as the other side of the coil running down the frame to the points inside the cam cover from underneath. Any one of those has a "pinch" potential. It could be the wiring at one of the two switches or the switches themselves as well. While you are at it make sure the battery and regulator wires have good firm contact. They are all easy to get to and check. Get a factory manual soon!!!!!! You did not mention if this is an electric or kick start. Makes a difference.

 

With the problem you are describing, there is no way I would want to take off on a ride from Ill to Fl. Trailer it home and get the backfiring problem fixed. Most likely you will encounter other problems as well on short rides at home.

There is a chance that the backfiring issue could be from a lack of fuel. My 75 would pop and jerk pretty bad at highway speeds and I found out that it was starving itself for fuel. The fuel tank, petcock, fuel filter (if you have one) and carb should all be cleaned out. That fixed my problem. Unless this bike was already a daily rider, it's a good idea to clean these parts anyway.

If you decide to ride it anyway and get stuck in those Alabama backwoods, call me. I'll try to get there before cousin Clem and Scooter start pinching your ear and tell you to "squeal like a pig". ha ha

 

Thanks for the advice, so far, it is a push button start for sure, It may have a kick as well, I'm not sure. I also am not sure if this is an electrical problem, or if it is coincidence that it stops after he has wiggled the wiring, may be heat related, and him turning the bike off to wiggle the wiring corrects the problem. I don't really have a way to trailer it home, I drive a beater with a heater, and have a nice bike, as my daily driver. I'm just getting to old, and have been a medic for long enough that my (oh what is it you guys call them...) "RiceRocket" kills the back. not sure if my beater old pickup will make it all the way, so its fly there, and spend a week fixing up the bike to ride it back, or drive two ways in the beater and fix it up when I get back.... dont really have enough $$ to rent a truck. I figure I will have to gather more information, when I get there and start looking at it. I just though there might be a common problem that, you guys might be able to snap out a quick oh yea they all have that problem its this...
Thank you all so much for the advice so far, I'm sure Ill have a ton more questions
Noah

 

The most common reason for a Sportster backfiring is because there is an air leak in the inlet manifold O rings.
If the carb has been removed lately (ask uncle) then that would be what I would check first.
If there is no brace on the carb (brace attached to the air cleaner backing plate on one end and the engine on the other end) that will allow the carb to droop and create an air leak.

But, wiggling some wiring does not stop an air leak. So if that is a legitimate fix, then it is not an air leak.
Check the wire connections on the voltage regulator and make sure that are connected tightly.

This very difficult to diagnose with so little information. There are a number of things that can cause backfire, and an air leak is right there at the top of the list.

Good luck to you on the ride, should you decide to do it. If the Sporty was in tip top condition, a ride from Florida to Illinois is still quite a trip on a Sporty.

Be aware that if the bike has the 2.2 gal gas tank your range between gas stations is going to be no more than 65 miles, with 75 being the absolute outside limit.......... Don't ask how I know that.
pg

 

As PG wrote manifold air leak is on top of the list... then I'd look fuel filter inside of petcock, to do so you need to remove petcock. Sametime you can flush fueltank.
If you find "someting" it would be wise to clean carb.

and with 3,3 gal "king tank" you could get 100 mile distances..

 

My 77 XLT started backfiring bad 1 day, problem turned out to be the pos cable was grounding out sometmes.