Exhaust backfire?

First off...Thanks for all the input as to my clutch cable adjustment problem. I got it fixed..seems that when I put the cover back on the clutch release mech. wasn't seated correctly.
Now on to bigger and better things. The bike was always hard to start ever since I got it (2 months ago). Now not only does it NOT start, it backfires (sounds like a shot gun going off)
I've had the battery on a trickle charge, so I know that's not the problem with starting and yes the fuel is turned on and yes I put in new plugs. Any ideas?
As far as the backfiring... I had the carbs off once already,they looked clean, maybe the jets need attention or could it be the carbs aren't in synch?

Are you running points? It could be ignition rather than carburation.

The reason I ask is I installed dyna coils with wiredgeorge mod but kept running points. After 3 months it was hard to start and would backfire loud like you describe. I traced it to my condensers, the power from the coils was to much I guess. I installed a dyna ignition and problem solved. Starts every time now. If you can turn off your headlight while cranking you will get more juice to ignition and maybe she will start so you can diagnose the problem. Good luck as it is probably something simple hopefully.

OldHippie wrote:

... does it NOT start, it backfires....

If ignition has a mechanical advancer, would check it to assure not being stuck in the advanced position.

Could do static timing check to assure correct F mark alignment.

Would also perform compression test (or better yet, a leakdown test) to help determine whether an intake valve is leaking. First "dry" compression test, then "wet" (teaspoon of oil put inside through sparkplug hole) compression test. Remember to hold throttle wide open during compression testing.

Comparing psi figures between dry and wet compression tests often helps determine whether a valve is leaking, and extent of blow-by past piston/rings. The leakdown test identifies which valve (intake or exhaust, or both), and amount of blow-by past pistons/rings into crankcase.

Then check all valve clearances and adjust to specs if needed.

Good Luck!

If ignition has a mechanical advancer, would check it to assure not being stuck in the advanced position.

Could do static timing check to assure correct F mark alignment.

Hey thanks I didn't think and the advance.

Have look into getting the kit for compression tests, got the manual for the bike so I should be able to do the static timimg bit.

anytime i start a bike and it backfires at idle i go after the idle circuit in the carbs, looking for blockage and a lean mixture. sometimes points will arc when closed, might want to clean them and look for pits and burns. when condensers go out they burn on the points contacts. If the mix. screws make no change in rpm when turned in and out and the lean backfire is present suspect the idle circuit passage blocked on one or more carbs. any vac. leak at the boots can cause backfires. A fouled spark plug firing on alternate strokes can ignite fuel in the pipes. check for dry plug or plugs when diagnosing carburation.