I apologize if this is a possible repeat of a previous thread. Too many to look through to make sure...

Ok, here's where it all began..I bought a 1976 Sportster Ironhead 1000cc a few months ago. It ran like brand new up until just recently when it started behaving badly. It started to buck like a wild horse in fourth gear traveling down the highway...(I feel like I could get long winded with this so I'll get to the point)

The problem would seem to fix itself and over a matter of a few more rides it got worse,,,fast forward to today and now I feel like I have a big paper weight sitting in my garage.

I removed the starter, generator, and voltage reg. Everything was good except the voltage regulator. Brand new VR (94.00) installed. Fuel filter had a bunch of debris in it. Wallah! That must be the problem! New fuel filter and line (10.00)....point adjusted (gap 0.018/45mm). Now when I try to start it turns over but it seems like no sound is coming out of the pipes. I hit the start button four more times and it eventually acts like it wants to fire with a poof of white smoke out of the carb and a loud unnerving clank sound from the clylinders like a wrench is bouncing around with the pistons. Maybe the fifth try it fires up but loudly backfires out of the rear exhaust pipe over and over again about every two seconds.

I've taken the plugs out and hit the starter and have good compression coming out of both holes. The plugs get blackened very quick after I clean them but I can't keep the bike running long enough to adjust the mixture. I have not messed with the timing but then again it was fine before and I can't get the bike running. I'm worried about the clanking/slapping coming from the engine.....

Before anyone goes off on me.....I am a new guy to all of this having decided to buy my first Harley at the age of 32. I am wanting to learn as much as I can, hince the reason I bought an older bike.

Any help would be much appreciated.

Thanks,
Colin

 

Time to pull the cyl's off to check the rods/bearings etc

 

When mine was bucking like that, it was some rust in tank getting in fuel and clogging lines. Had to clean my tank and coat with some caswell epoxy (made for fuel tanks for gas and alcohol) Then dropped bowl on carb and replaced fuel lines and filter. Since you found dirt in the filter, I would get that cleared up first. Got some bad gas once that had some water in it and it did the same thing and was a bitch to start. While tweeking my carb, I got it too rich at one point and it would bark and puff white smoke out the carburetor. Debris might have gotten in your carb messing your float up causing it to be way rich. I'd check the oil and see if it smells like it has gas in it or just change it out, oil is cheap.

 

I just had the same backfiring problem with my 80 it turns out my problem was timing it thought for sure I had it correct the first time i set it but after double and triple checking i was off a bit on my advance time. I got the backfiring to stop but now I'm not getting constant fire in the back cylinder. as for the bucking in fourth i don't know enough to help with that one.

 

Thanks guys! I've also been thinking I need to do a little rehab on the tank due to the debris found in the filter and line. What is the best way to clean and coat a tank with only the small hole. I've seen the kits before...., are the instructions right on or are there some tips you can let me in on? And also, to take the cylinders off, is there any way to avoid having to take the entire engine off?

Thanks again for the reply's and help!

 

The tank sealing kits are pretty good. A little messy but it can't be helped. After you get the fuel tank straightened out. Check your advance mechanism and your timing. A bad set of flyweights will give you all sorts of grief. Check your manifold seals, wiring and every other simple thing you can think of before tearing into the motor. Nothing is more aggravating than spending tons of time and money only to find the problem could have been fixed in a couple of minutes.

 

Before you start with too much work like pulling the heads. Try first looking at the push rod adjustment. That clanking noise could very well be a loose push rod clanking around in the tube. Which it will also cause the problem starting and running like you mention. Especially if one is completely undertightened and it's not opening the intake valve or exhaust valve.

Just a thought.

 

Ditto - check the pushrod adjustment before tearing into the motor. If you have a compression tester, check that also before doing anything more serious. I'd check the static timing and condition of the advance unit and condenser, too. You can remove the top end (heads and cylinders) without pulling the motor out of the frame. If you don't have a factory shop manual, get one and look it over before you try anything involved.

 

When mine started doing the bucking thing in 4th gear at around 55-60mph it would only do once in a while and continually got worse. I found that because my carb did not have a support, it sagged from the weight and too much air was getting in through the intake seals, causing it to buck and sneeze. After a seal and clamp replacement and carb support, it runs perfect. Like 83XLX said, make sure the compression is good on both jugs.

 

i agree to check the pushrods, if they are too tight the valves wont seal and wont have compression. therefore will not fire or if it does it will run like crap as if out of time.