Sticking? Not too likely but could be bent or have a busted/worn valve spring but these things rarely happen on the super durable 1500 engine unless through accident, misuse or abuse.
Well I painstakingly checked all 6 wires....what a freaking job. It's a bitch getting those things reconnected, especially with an engine that is still very warm. I ran an OHMs test on all the wires and they appeared to be fine. Too much trouble test the coils....lol That'll have to be for another day. But at this point, I'm certain the wires are fine. They are protected by a heat sleeve, and none of them appear to have any insulation damage. I ran the engine after inspecting them, and sprayed each one down with water; there was no change to engine operation. So at this point, minus the possibility of bad coils, I'm going to call the ignition system good...for the time being. And since the backfiring inside of the intake manifold only seems to happen on the left side, that is the side I will concentrate on.
What I do know (or at least strongly believe) is that the left and right intake manifolds SHOULD have steady vacuum. There should be no wavering or erratic bouncing of the needle at idle (vacuum gauge needle). I agree with you that the GL1500 is a super reliable bike, but unfortunately had a very unreliable owner who left his bike parked outside in the snow and in the rain without any shelter or cover WITH ethanol BTEX fuel and that without any fuel stabilizer or treatment. He is doing the very same thing to the Goldwing he has now...sold this one to me, and bought a 1998 model with over 300,000 miles on it. The guy who owned it prior to him was a motorcycle racer, so their might be some possibility for abuse. The owner before the gentlemen I purchased the bike from modified his exhaust system by cutting the baffles out of the stock mufflers, and installed end caps (chrome). I'm not sure about Goldwings, but on V-Twin Shadows, it is almost a MUST to rejet the carbs when free-flowing exhaust has been introduced to the system. The larger jets is needed to increase fuel delivery in order to reduce popping in the pipes. I'm curious if the free flowing garbage that's on my bike now might be calling for a rejetting of the carbs....I doubt it, but just a though.
Okay so I'm at a stand still for tonight...bike is all torn down. I'm not yet convinced the carbs are the problem, nor the ignition system, so I'm going to write those two off for now. This leaves possible vacuum leaks from a hose underneath the intake manifolds, or the intake valves. If an intake valve is not sealing well, it will not close tight enough and so blowby will seep past the valves and back into the intake manifold; this is easily identified by a shaky vacuum gauge.
Exhaust valves are the most common ones that leak with enough corrosion. However, because oil companies reformulated their fuel mixtures in the late 90's, mixing BTEX additives to the fuel, engines of all kinds have been failing far too early, mostly from clogged or damaged fuel systems, or gunked valves. BTEX stands for Benzene, Toluene, Ethylbenzene, and Xylene. Tests show that Toluene and Xylene are very destructive to plastics, seals, and copper. It is my opinion that the oil companies added BTEX to intentionally damage engines so that consumers would blame this on the ethanol industry. Ethanol is not corrosive as people assume; it's BTEX that is doing the dirty work, while alcohol gets the blame. Ethanol, which can be made from many resources such as trash, food wastes, wood, certain crops, and even plastic wastes is a very good renewable energy source. While its BTU output is less than gasoline, this can be compensated by forced induction systems (turbo), increased cam duration and lift (for increased compression), and/or advance ignition-timing.
My point is that BTEX, when unburned, can leak from faulty fuel injectors or leaky carbs, and buildup around a closed intake valve. Gasoline will evaporate over time, leaving a small oily residue. Alcohol will also evaporate leaving little to no residue. But BTEX, oh boy that is a different story. This crap forms a hardened candy-apple type coating that is hell getting off. It dries up into a carmel state and once completely hardened, it will require a drill and a wire brush to get it off. I found this out when I rebuilt my Chevy engine, and it was my intake valves that were caked with this crap so bad that I literally had to use a grinder to get it off. Not even soaking the valves in parts cleaner overnight would remove the stuff.
The previous owner ignored his carburetor issues, and his floats were likely sticking, and so fuel would leak down into the intake manifold, which we all know is bad juju. It is my opinion that the clicking sound I am hearing is lifter noise, likely from a sticking intake valve from the foremost cylinder on the left side (I do not know which cylinder number that is yet). Since the poor bike was left in the snow and rain for even 2 years straight with little to no riding, it is likely some (or one) of the intake valves is sticking and not closing all of the way. So for now, I'm using B12 Chemtool fuel treatment which I hope will dissolve any buildup. If not, and it turns out the intake valve is indeed sticking, then I may have no choice but to remove the heads and have them cleaned and relapped. In a few moments, I am headed to the parts store to pickup a can of seafoam spray and I'm going to let the engine soak over night. Oops! So much for that idea...didn't realize it's almost 10:00PM. LOL So guess it will have to wait til morning.
I'm open for other suggestions folks. Believe me, I do not want it to be the valves. Where's a freaking Jeany when you need one. Major Nelsen didn't realize how lucky he was to have such a fine, hot, and attractive Jeany. LOL
Good night all!