preignition, detonation, or backfire?

[Guest]

OK, I am on my way to work this morning on the bike, 82 1100GL and about 8 miles in I get what I think is a backfire on the interstate. So powerful I could feel it through the seat, footpegs and handlebars. I think whoa that was weird, but the bike is still running strong. I keep on going and about 2 miles later it starts doing this softer and louder and more consistently. By the time I got to work, my ride is only 15 miles total, the popping and banging was almost constant at 55 to 65 mph. All of the popping and banging is accompanied by a slight tapping feeling through seat and such. Pull in the parking lot at work and at idle the engine completely stops making the racket and goes nice and smooth at low rpms and idleing.

Anyone have any ideas on this? I have covered all of the commen maint. issues with the bike, as far as my noob self is concerned anyway. Done all the basics, oil change, valve clearances, carb dip, new plugs, new o-rings all around from Mr. Barr., new petcock, vacuum sync, air filter.

So far as I know the carbs are all set to stock and I have the stock exhaust. Mix screws are at 2.5 but that wouldn't affect my cruising speed mix would it?

Ah heck I am so confused now. I hope she gets me home without going under.

Thanks for any advise!
Parker

[rustybronco]

spark plug wire going bad or loose on plug, voltage to ignition coil intermittent, cdi module going bad, but you should feel the engine dropping a cylinder(s) before it back fires.
recent fill up with fuel? possible water in fuel or bad fuel.

[dr_fosg8]

Thanks for the ideas rustybronco. I will check the caps for tightness to the wires and the plugs when I leave work. I did just fill up with gas (mid grade 89 octane) but I had about 22 miles on the tank of fuel before this mornings trip.

Now for the important question. Am I going to destroy my engine if it continues on my ride home and I keep going?

P.S. I don't feel any loss of power at all ( at least that I have noticed ) while it was happening. Ie, loss of a cylinder.

[rustybronco]

I would take it easy going home.
if there is water in the fuel or a intermittent spark condition, you should feel a loss of power or notice a bad running condition.
If the backfire is great enough, it could do damage to the exhaust system and/or mufflers, if they are in a weakened state (thin).

just a suggestion, get some dry gas and try it.

I wish I could think of something else that would be the cause of your problem.

[dr_fosg8]

I will take some back roads home and ride slower.

Is there a way to test the wires and caps to see if they are bad? I have stock coils and from what I have read it is hit and miss as to whether the wires will or will not come out of the coil for replacement.

So exhaust pipe damage is the worst of it? The pipes I have are in good shape and solid so I won't worry about that. I was concerned about engine internals being damaged. Valve rods, pistons, connecting rods and bearings.

Again, thanks for the input.

[rustybronco]

Is there a way to test the wires and caps to see if they are bad? I have stock coils and from what I have read it is hit and miss as to whether the wires will or will not come out of the coil for replacement.

So exhaust pipe damage is the worst of it? The pipes I have are in good shape and solid so I won't worry about that. I was concerned about engine internals being damaged. Valve rods, pistons, connecting rods and bearings.

Again, thanks for the input.

yes there is a way to test them with resistance readings. but that won't tell you if you have a coil going bad under heating conditions, substitution of the coil will.

engine internal damage is a slight possibility, but I think it would have to be the cause, such as a broken valve spring and that could be detrimental to the pistons, rods, ect.

do you notice any valve train noises?

have you since tried starting it?
if it starts easy and runs fine at first, then sometime after running gets to backfiring again, suspect a component going bad when it heats up, such as a coil, pickup coil, ignition box.

[dr_fosg8]

Update!

Ok folks I went to ride away from work today and the bike fires right up and is running good. Put it in first and ride away then wham! The banging started right up. I am speculating that the U-joint in the drive shaft is the cause. Mainly because there are fine metal shaving around the rubber boot that covers the U-joint. It is part 34 on the fiche for final drive at bike bandit and it is you guessed it, discontinued.

I will have to try to get the bike home tomorrow night in a buddies truck. I will take some pics of what I find behind that boot when I get her home.

[SqDancerLynn1]

Pull the boot back It could just have loose bolts.

[dr_fosg8]

Holy sheeet!

Went out to the bike at work this morning and pulled back the boot covering the U-joint assembly and found that one of the bolts that connects the drive shaft to the secondary assembly had come completely out and was bouncing around inside the boot!

Well the good new is that I know what the problem was/is. Now I have to attempt to fix the damage done to the back of the engine case where the secondary exits the engine case.

I will post some pics of the damage tonight or tommorrow.