2004 gs500 at my wits end....

[cloudscrash325]

Hi all! Nice to meet all of you. I'm completely new to the forum and Iv looked over the site for my issue.. I can seem to find anything relating to my situation.

So for starters. My best friend's nephew bought a 2004 Suzuki gs500 in 2008
He ended up becoming a marine and never returning home.
I got a call about a week ago from my friend. He said he can't look at the thing anymore
And it's taking up to much space. He drops it off. Now I know my way around carbs and a bike.
But this one was puzzling. First off the last time the bike ran was in 2010
Tank is rusted internally. Carbs were some of the worst Iv seen. I cleaned everything out rebuilt and
Rebuilt the carbs. Re jetted as well for pods using this site ! Last night I got everything back together
To sadness. Bike still won't run. I tried starting fluid. To see if I'd get a response
To a defining loud bang I was pretty much at a lose for hearing for 30secs.
Replaced the spark plugs this morning same issue. Loud bang. I also tried ruling out the tank and feeding the carbs manually with a bottle and a line going right to the carb directly.

So now I'm at a loss. I feel like the carbs are in reverse. Fuel is shooting out the back of the intake.
I'd like any possible insight on this situation. This bike is in wonderful condition. And seeing as how I got it for free. I don't mind putting time or money in to the project. I was just really excited to get it running with the nice 2 weeks a head of me. Not much time before winter comes knocking at my door lol

Thanks all and I'm glad to meet all of you!

[Sporty]

Ignition or valve events are happening at the wrong time. Or the exhaust valves are not opening.

The exact cause I cannot say, but this what I'd be checking.

Make sure the coil primary wires are on the correct coils. Make sure that the pick up amp reluctor/ rotor are correct under the RH ignition cover. Check grounds.

Perform a compression test.
If low compression,
Remove the cylinder head cover, (baby the gasket, carefully pry the half moon cam ends up with the cover gasket) check that everything thing is working. Turn the engine over from the 19mm reluctor bolt and verify that everything lines up as it should when performing a valve adjustment.
Check valve clearance.  (Look up Baltimore GS videos on YouTube).

Shop manual here http://forum.gs500.pl/ftp/Studi/Suzuki_GS_500_E_F_1989-2009_Service_Manual.pdf

[cloudscrash325]

Thank you very much for the quick reply. I'll check all that's stated above.
My question is how would valve timing go out of wack without someone already tampering with it?
Sorry I know carbs and almost nothing about engines 

[Sporty]

Thank you very much for the quick reply. I'll check all that's stated above.
My question is how would valve timing go out of wack without someone already tampering with it?
Sorry I know carbs and almost nothing about engines 

My pleasure, just checking and posting on lunch break.

popping back through intake is a classic symptom of valve timing off/ exhaust valves not opening. I can come up with scenarios, but it will reveal itself as you diagnose.

Ignition can certainly cause misfires so that has to be checked too.