Won't start, BIG BANG! backfires at the end of each attempt

[JanetsMechanic]

83 with pamco electronic ignition system from Mikes (also their replacement stator alternator charging system).

Was working great for a couple of months after installing the new electronics. Bike then sat for a while and then fell over hard in the grass (on its right side) now it won't start and as soon as you release the clutch or hit the kill switch after turning it over it backfires so loud that it scares the crap out of you. I have checked compression - good. I can see spark when I pull the plugs and hold them against the block (I can't tell if it is "strong" or not - not enough experience). Seems to have fuel flow and I have replaced the gas in the tank a few times now. I have tried starter fluid and nothing seems to make it fire when I am cranking it over. Then BANG again when I stop. It seems like timing is the most likely but the new electronic timing system has very little adjustment and I have tried it "in the middle" as well as advanced and retarded all with the same result. I have tested the coil and wires for ohms and continuity according to the manufacturer specs and it seems to be in spec. I have tried and test a LOT more but absolutely no change in behavior.

I am desperate for suggestions.

 

[Signal]

Bike ran fine but after sitting 2 months it won’t start and you have altered the timing. My immediate thoughts are that the fuel has gone off and the battery is low. These are two things that “go off” when a bike is sitting.

Put the timing back to where it was, it is unlikely to have changed. You may have to go through the Pamco instructions to get it back to the static timing position.

You have replaced the fuel in the tank, have you drained the carbs? If not drain them, stale fuel could still be in the bowls.

Charge the battery or better replace with a known good one. Your battery may have lost some electrolyte when it was on its side.

A low battery will crank the motor but the load decreases the battery voltage to a level where the ignition will not work. When you stop cranking the voltage rises and the ignition fires. Low voltage makes electrical components do funny things.

The fault finding wizards will hopefully chime in with some more suggestions.