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backfiring?
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Author:  hauser2169 [ Wed Jan 26, 2011 11:52 pm ]
Post subject:  backfiring?
I havent been out in the barn to work on the bug because of school, but this weekend i will. last time i ran it, well just about all the times i ran it it would backfire. sometimes out the carb but mostly out of exhaust. i triple checked my valve clearenance. the only thing i can think of is that it does have empi heads on it. would those heads have different valve tolernces then stock? any ideas?
Hauser
Author:  passat2800 [ Thu Jan 27, 2011 12:12 am ]
Post subject:  Re: backfiring?
What are the symptoms of a frozen busted dellorto? Ain't it black smoke and popping?Not sure.
Author:  DVS1 [ Thu Jan 27, 2011 11:50 am ]
Post subject:  Re: backfiring?
Most of the time I had a problem like that there was a crack in the head. Or sucking air from a loose or torn Intake gasket. Just my experience
Author:  eighty3bronco [ Thu Jan 27, 2011 2:00 pm ]
Post subject:  Re: backfiring?
could be timing too...
Author:  chris38375 [ Thu Jan 27, 2011 10:22 pm ]
Post subject:  Re: backfiring?
exhaust gaskets will do it too
Author:  passat2800 [ Fri Jan 28, 2011 12:44 am ]
Post subject:  Re: backfiring?
Maybe a stuck intake or exaust valve or both.A weak sring or tight valve guide ain't letting the valve close fast enough. A bent valve stem and a warped or burnt valve. ALWAYS do a compression test.A wo' out valve guide will let raw air into the exaust and make a pop and make an intake leak on an intake valve.Does it smoke when you let off the gas?Oh. While I am on the subject, Do not ever put a new head on used jugs. "New motor" cylinders and heads wear together thru time. You come along and put an air tite head on old jugs the new vacumm will suck oil up past the rings on the intake stroke. It will smoke!And foul plugs.
Author:  davehix [ Fri Jan 28, 2011 1:30 am ]
Post subject:  Re: backfiring?
Does it do it all the time? idle? mid Throttle? full?
Author:  ehale [ Fri Jan 28, 2011 7:40 am ]
Post subject:  Re: backfiring?
Wipe out the distributor cap moisture will cause it to run bad also a crack in the cap will too
Author:  gasman [ Fri Jan 28, 2011 9:22 am ]
Post subject:  Re: backfiring?
If back firing through the carb I'd say you have some sort of ignition problem.timing,distributor cap busted,points,weak coil,something that route.back firing out the exhaust you got air leaking somewhere I'd say.intake gaskets,carb gasket,in the head somewhere,cylinders.you need to give a little more info.does it back fire bad or just a constant little popping,does it get worst or better the longer it runs?when does it run best,idle or wide open.more info would help narrow it down and limit all the things that could be wrong,I mean it could be a lot of different situations.Chad :mrgreen:
Author:  hauser2169 [ Fri Jan 28, 2011 11:15 am ]
Post subject:  Re: backfiring?
It gets worse the longer I run it. I thinlnim going to do a compression test. As well as a leakdown test.my ignition is electric. New gaskets on intakes. Kinda weird
Does this sound like a air leak or burnt valve?
thanks again
Hauser
Author:  kevin f [ Fri Jan 28, 2011 8:40 pm ]
Post subject:  Re: backfiring?
Get some starting fluid and spray around all the joints of you intake, around carb. Also is running a single carb check the rubberintake boots. It sounds to me like you have an air leak. If you spray the starting fluid on the leak the motor should rev up or try to stall. If you notice any change in the sound of the motor you found your leak.
Author:  Firebug [ Fri Jan 28, 2011 9:27 pm ]
Post subject:  Re: backfiring?
kevin f wrote:
Get some starting fluid and spray around all the joints of you intake, around carb. Also is running a single carb check the rubberintake boots. It sounds to me like you have an air leak. If you spray the starting fluid on the leak the motor should rev up or try to stall. If you notice any change in the sound of the motor you found your leak.



I think it was you Kevin that had an intake coming apart at the seams and was popping bad,, and fixed it with some JB weld.
Author:  kevin f [ Fri Jan 28, 2011 11:00 pm ]
Post subject:  Re: backfiring?
Yea marty I had one do thart once. The intake was leaking where the metal tube goes into the aluminum casting. I pulled the tube out of the aluminum, cleaned it good and spread a coat of JB weld on it and stuck it back in. As far as I know its still running after about 5 years.
Author:  passat2800 [ Sat Jan 29, 2011 12:48 am ]
Post subject:  Re: backfiring?
Coils play games on their way out.Such as get worse as it warms up. Pull up coil checking vw aircooled. The compression is blowing back up the carb or exaust because the timing is off.Do you have a droop in the fuel line b4 the carb to catch moisture from the tank? After a COLD winter, I'd look into a busted carb.Add a little gumout or stabil to gas so your gas will stay dry.
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