Author Topic: backfiring, bike won't start womp noise  (Read 1267 times)

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Greg

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backfiring, bike won't start womp noise
« on: February 21, 2006, 09:59:35 PM »
hi all
so a few months back my 76 750f was hit by a dummy. i warngled with the insurance for about 6 months and the bike just sat there. the other day i tried to start it up.
after a few cranks with the starter she stumbled to life, backfired, blew dark smoke, and then died.
few days later tried again. couldn't get it to catch, strange "woomp" noise from one of the cylinders as she tried to start, lots of backfiring, even blowing fire out the pipe on a couple of occassions.
adjusted the timeing and dwell. funny squeeking coming from the engine as i manually rotated the crankshaft.
tried again. nothing.

i thought maybe it was the timing, but i fixed that and it doesn't seem to help. pulled plugs on cylinders 1 and 4 - both were wet with gasoline and had a good deal of carbon on them.

any thoughts? what else could i look for? a friend suggested the backfiring meant that an exhaust valve was sticking open - any truth to that?

thanks everyone!

greg

Offline scondon

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Re: backfiring, bike won't start womp noise
« Reply #1 on: February 22, 2006, 12:42:25 AM »
so a few months back my 76 750f was hit by a dummy. i warngled with the insurance for about 6 months and the bike just sat there.

What was the extent of the damage to your bike, specifically the engine/cases. Did it lay in a ditch while you were in the hospital?
I've picked up a bike that got knocked over and lay there for an hour and it was a real #$%* to get started even though there was no damage. Also had a bike sit for nine months and it would not do anything but shoot booming clouds of smoke until I thoroughly cleaned the guts of each carb.

     Install new plugs. Check that you are getting spark to each. If not then I'd check for damage to the points plate or timing shaft, coil damage or disconnected wires(hard to guess what may have been damaged so let us know). Remove the airbox and spray carb cleaner directly into air intake of each carb then try to start the bike. If it runs good for 2-3 seconds then I'd pull the carbs and clean'em and check float heights.Fuel, air, and spark in the right amounts and at the right time. Check'em all. Hopefully it's one, or a combination, that needs attention and not something serious requiring an engine teardown.

a friend suggested the backfiring meant that an exhaust valve was sticking open

Bad timing, fouled/improperly set carbs, rats in the airbox are but a few causes of backfiring.

     
strange "woomp" noise from one of the cylinders as she tried to start,

Alright now, which is it, a "woomp" or a "womp"? Makes all the difference ya know :)  Seriously though, could be compression escaping or it could be just the sound of a non-firing cylinder going up and down and you never heard it before 'cause the bike usually started right up.
Give me..a frame to build a bike on, and my imagination will build upon that frame

Greg

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Re: backfiring, bike won't start womp noise
« Reply #2 on: February 22, 2006, 07:30:31 AM »
Sean
Thanks for the reply. I'm the guy you met on Saturday at Tyler's shop. Funny to see you here!

One other thing that I forgot to mention was that I rode it home from the original accident, 7 or so months ago.

I'll pull the carbs and clean 'em and then report back.

Thanks again!

greg

Offline scondon

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Re: backfiring, bike won't start womp noise
« Reply #3 on: February 22, 2006, 08:19:57 AM »
Ah yes, Greg with the blue 550 Four. If you rode it home then I'd be leaning away from any catastrophic engine problems. New plugs, fresh charge on the battery, pull the float bowls and make sure there's gas in each, try the carb cleaner starting trick(no more than a couple times). You've got my number, give me a call if ya need any help with the diagnostics, always happy to..
Give me..a frame to build a bike on, and my imagination will build upon that frame