Harley Question????

[ctraylor]

I am working on a friends 98 Harley 1200 Sportster. It runs descent cold but as it warms it starts to backfire through the carburetor and the tail pipe. It acts like it is starving for fuel but I know it is getting fuel. I have replaced the coils with known good coils but still the same thing. Has anyone had this problem before? I know this is not a Harley forum but I need some help on this one.

 

Thank you,,,

[Squidley]

The 1st thing I would look at is if it's sucking air someplace. It's a CV carb, so the concept is the same as our Ventures. A vacuum leak somewhere, or a line that has come off. Did you work on the carb at all? Just throwing out some random thoughts here....

[ctraylor]

I can see the slide working when you twist the throttle but you are right there might be a vaccum leak on the carb. base. I think he had the carb. off. I will check that.

[SilvrT]

There is a mixture screw on the carb hidden behind a plug that might need adjusting. You have to drill out the plug to get at it. I had to do this on my son's '03 Sporty and it cured the backfiring (mostly). I say mostly coz I don't think anyone can totally eliminate it from all operating conditions.

 

If you do a google search on this I think you'll find some technical writeups about this and what to do. I didn't save the info I had.

[Guest tx2sturgis]

I am working on a friends 98 Harley 1200 Sportster. It runs descent cold but as it warms it starts to backfire through the carburetor and the tail pipe. It acts like it is starving for fuel but I know it is getting fuel. I have replaced the coils with known good coils but still the same thing. Has anyone had this problem before? I know this is not a Harley forum but I need some help on this one.

 

Thank you,,,

 

 

Is it backfiring on acceleration, steady cruising, or on deceleration? Choke open or closed? Different operating conditions when its backfiring would help us to help you. Its unlikely that the engine backfires during all these conditions. 'Backfiring thru the carberetor', do you mean its doing what we call a carb-fart? Or is it a true 'backfire' thru the aircleaner?

 

Feel the backside of the aircleaner. If you feel the plastic aircleaner housing, then most likely the stage one has never been done. If you feel empty space, then do your fingers pick up black oily residue? is it dry, dirty, and black? or is it wet and very oily?

 

Spark plug wires on a 15 year old bike are suspect. So is the fuel filter, the stator/battery/rectifier combination, and of course, it never hurts to run some fuel system cleaner thru the bike, such as Seafoam or Startron.

 

Just a few things to look for.

 

 

Edited February 2, 2012 by tx2sturgis

[ctraylor]

It is severly backfiring back through the carb and out the muffler. You can hold the throttle at a constant and it will blow fire back through the carb and out the muffler.

[Guest tx2sturgis]

It is severly backfiring back through the carb and out the muffler. You can hold the throttle at a constant and it will blow fire back through the carb and out the muffler.

 

When you say hold the throttle at a constant, do you mean its backfiring going down the road? If so at what speeds, 10 mph? 50 mph? 70 mph?

 

Or does it backfire only when sitting still and parked, and someone whacks the throttle open and holds it?

 

Or does it do this moving AND stationary?

 

Im just trying to get an idea of what exactly is happening.

 

Bear with me.

 

 

[Caveman]

Done a valve check?

[Scooter Bob]

My 83 sporty did that. It was a bad electronic ignition module that kept throwing the timing around, early sometimes, late sometimes, and others where it belonged.

 

Also +1 on the valves, maybe. I think the evo sportys had hydraulic tappets, but might still be adjustable.

 

Just my $.02, Scooter Bob

Edited February 2, 2012 by Scooter Bob

[Scooter Bob]

Another thought related to timing...

 

I believe there is manifold vacuum sensor that helps decide where the timing should be. Might be a much cheaper place to start than the brain box. Maybe a broken vacuum line to it even.

 

Later, Scooter Bob

[tazmocycle]

i had a friend who had a siimar problem but not as bad. after running for several miles it would foul out the plugs. after changing out a couple set of $15 harley plugs he found a vacuum leak on a little hose thats hard to see, maybe the vacuum avance hose. after replacing it it ran fine. another friend who had a new harley with fuel injectors had one cylinder missing and mifiring, the harley shop put 5 ign mods on it and it still ran the same. they brought a factory tech in and a few weeks later found that the wiring going to the injector had been strechedout real thin and was not getting enough voltage to make it work properly. sometime it take a little head scracthing to figure it out!LOL!!

[muaymendez1]

I say you atre doomed.You will never get rid of that knock

[Snarley Bill]

sounds like a clogged pilot, or main jet.