Backfire

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Backfire

Post by peregrine67 on Wed Aug 18, 2010 6:35 pm

So she's been running just fine for the last few months. I even got her up to 75 on the freeway today. However, lately when I let off the gas in second or third and put a drag on the engine i get some mild backfiring. Suggestion? I'm hesitant to play with the timing since otherwise she's running so well.
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Re: Backfire

Post by aircooledaddicts on Wed Aug 18, 2010 7:44 pm

It could be the mixture on the carb being a little rich or a leak in the exhaust somewhere.
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Re: Backfire

Post by peregrine67 on Wed Aug 18, 2010 8:53 pm

It's fuel injected. I'll dial back the mixture a little bit.

I do think I have an exhaust leak somewhere. I just didn't realize that would cause backfires.
Thanks
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Re: Backfire

Post by meinvw on Thu Aug 19, 2010 9:32 am

Are you running the stock dizzy? Check your dwell on it, that can cause a backfire as well as an exhaust leak.
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Re: Backfire

Post by meinvw on Thu Aug 19, 2010 9:35 am

Oh yeah, do not hesitate to check the timming, you can be a bit off and it run great but will do some damage if not dead on. A friends bus is back in the shop with a chunk missing from his exhaust valve on his 74, not sure what caused it but thinking his timming was off.
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Re: Backfire

Post by peregrine67 on Thu Aug 19, 2010 10:31 am

meinvw wrote: Are you running the stock dizzy?
What's a dizzy?
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Re: Backfire

Post by peregrine67 on Thu Aug 19, 2010 10:41 am

At this point I'm sure I have the exhaust leak. I'm gonna work on that and then see what I need to do to the timing. Thanks guys.
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Re: Backfire

Post by Grifspop on Thu Aug 19, 2010 11:14 am

peregrine67 wrote:
meinvw wrote: Are you running the stock dizzy?
What's a dizzy?

slang term for Distributor
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Re: Backfire

Post by peregrine67 on Thu Aug 19, 2010 12:57 pm

Sorry, I should have known that. I've been out of the loop for too long.

Considering the previous owner put in a motor out of a 412 I don't quite know what stock is anymore. Stock to the bus? stock the 412? is there a difference?
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Re: Backfire

Post by Bugman114 on Thu Aug 19, 2010 7:08 pm

well if its a 412, you'll want what ever is stock to the 412. just because its in a bus, doesn't nessecarily mean you should put bus parts on that 412 (unless they are the same motor, i have no idea). I wouldn't put VW parts on a baja with a subi conversion Laughing

Finding the exhaust leak should be too hard. You'll prolly see black carbon wherever the leak is.

Like in this pic of a snowmobile engine, the area around the leak will be covered in carbon
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Re: Backfire

Post by Hobug on Thu Aug 19, 2010 10:11 pm

A 412 engine is a type 4 like a bus. The exhaust components should interchange. I have a type 4 from a Porsche 912 with VW 411 heater boxes and a 72-74 bus muffler.
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Re: Backfire

Post by vwtattooed on Fri Aug 20, 2010 7:46 am

if you have any Type 4 questions call Jake Raby at Raby's Aircooled Technology or Dave McCutcheon over at DTM Engineering. both are VERY knowledgable and can set you up with any parts you may need.
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Re: Backfire

Post by peregrine67 on Tue Sep 14, 2010 11:01 am

Okay I've located the leak but I need some advice on how to fix it. The muffler flanges on the driver's side isn't quite square with the passenger side. So if I tighten the driver's side down first it opens up the passenger side on the bottom like 2mm. And if I tighten the passenger side first the driver's side is open on the top about 2mm.
So what do I do? I know I could solve the problem with just a thicker gasket on both sides. The old asbesos one I took off was about a 1/4 inch thick but it fell apart and I can't reuse it. None of the parts stores had anything that I could make one out of either.
I was considing just making a ring of #6 copper wire and hammering it into shape but that seemed like kind of a ghetto repair to me so I wanted to bounce it off of y'all before I did it.
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Re: Backfire

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