1980 GS750L airbox turned fire ball??

[2005JJT]

I have been restoring a 1980 GS750L with the help from this site and feedback from the forums. Thanx to all with the help. Alright let me first start with whats been done. The bike had been sitting for 16 years. I did the carb clean, timing, a new battery, coils, petcock, airbox, air filter, gas tank and plugs. My last parts came in (petcock) so put it on and went to fire her up. After trying the choke full out for about 30 minutes. I sprayed 4 shots of starter fluid into the airbox and sealed it back up. I started to crank it with full choke and a massive back fire erupted my new airbox in to a fire ball. I had to spray it with a water hose to put it out. I cleaned it back off and nothing melted. It must have been a bad aim with the starter fluid. So I wiped it off and let it dry for about an hour and I tried to crank her again. She tried to start on full choke but wouldn't grab.
Shot two shots of starter fluid in it and started. This time it backfired or maybe not because wasn't very load and the airbox was on fire again. This time I blew it out like birthday candles. (screw the water to messy) My only question is why is it back firing. I'm about to try it again but now half the neighbor hood is afraid (my wife) or laughing there tatas off (everyone else). Please help.!!!!!

[gs54]

Try not to use the choke so much, I can flood my gs750L with just a quarter pull of the choke, for the first time try to push start it, it my be a better way for you to try and start it for the first time good luck.

[chef1366]

You have the 80 petcock which is a pos. Put it on prime and apply vacuum to the petcock and let the bowls fill and then run for the hills. You need a small slotted screwdriver. Up and down is prime.

[rustybronco]

I did the carb clean, timing, a new battery, coils, petcock, airbox, air filter, gas tank and plugs.

recheck wiring of coils and or spark plug lead hook up.

[2005JJT]

O.K. checked that bowls had fuel and refilled. I checked flow of petcock. It was perfect. I rechecked plug wires. They where going to correct cylinders. I am getting a backfire on 3-4 and 1-2 nothing.
I switched the plug wires 1-4 to 2-3. 3-4 still backfired but this time out the exhaust instead of airbox. I checked plugs still look new and rechecked gap .024-.028. I have them at .027.....I am out of ideas. The last thing is the plugs are dry. If they are not firing I would expect them to be wet. I can spray starter fluid on it and turn it over pull it back off and dry....Anything ideas.....

[chef1366]

Do a compression check.

[2005JJT]

I was thinking the same thing. Maybe tomorrow or early next week. I will pick up one and due it. Thanx

[chef1366]

Also check your valve clearance and cam timing.