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Tracking down a backfire problem - SOLVED - Thank you all!
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79SuperVert
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PostPosted: Sun Oct 17, 2010 3:34 pm    Post subject: Tracking down a backfire problem - SOLVED - Thank you all! Reply with quote

Short version: poor seal between J-pipes and muffler. Solution, Permatex Copper High-Temp Gasket Maker, then metal or asbestos rings and clamps.

Long version:

I have to find the source of the backfiring when engine braking. I can reach all the exhaust nuts except the two top ones on number one and three cylinders. Can I get to those by removing some tin in the engine compartment or do I have to drop the engine?
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Last edited by 79SuperVert on Sat Nov 06, 2010 11:43 am; edited 3 times in total
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Glenn Premium Member
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PostPosted: Sun Oct 17, 2010 3:35 pm    Post subject: Reply with quote

You should be able to get to them with a swivel socket.
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79SuperVert
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PostPosted: Sun Oct 17, 2010 3:48 pm    Post subject: Reply with quote

You mean like one of these?

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PostPosted: Sun Oct 17, 2010 3:50 pm    Post subject: Reply with quote

79SuperVert wrote:
You mean like one of these?

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EGGzackly
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79SuperVert
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PostPosted: Sun Oct 17, 2010 3:51 pm    Post subject: Reply with quote

Thanks.
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PostPosted: Sun Oct 17, 2010 4:07 pm    Post subject: Reply with quote

Or take a cheap box wrench and introduce it to your bench grinder. Personally, I like the brass nuts with smaller heads for these.
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Michael Fischer
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PostPosted: Sun Oct 17, 2010 6:30 pm    Post subject: Reply with quote

I use a half moon 13mm.
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79SuperVert
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PostPosted: Mon Oct 18, 2010 6:01 am    Post subject: Reply with quote

Never heard of those. This kind?

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[/url]
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79SuperVert
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PostPosted: Mon Oct 25, 2010 10:27 am    Post subject: Reply with quote

Swivel sockets worked nicely. Tightened the exhaust nuts and clamps all around. Had to loosen and move the heater boxes but that wasn't any trouble. Unfortunately, it still backfires. It may be that the gaskets are shot but I'm going to try other "easy" stuff first.

By the way, can the gaskets be changed out on the front exhaust ports easily? I suppose if I undo all the exhaust clamps the pipes can be moved forward enough to clear the studs.

The VW shop manual says that backfiring can also be addressed by turning the idle air mixture screw out 1/8 turn. I'm going to try that next.
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Harris
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PostPosted: Mon Oct 25, 2010 10:36 am    Post subject: Top nuts on Exhaust Reply with quote

If it's on your '62, make sure you have the the smaller 32mm asbestos looking gasket (muffler to J tube connection) I'm guessing here but I think the larger is 35mm and the smaller is 32mm. The 32 fits tight on the J tube. If the larger one is one there it could backfire. Mine did until I got the right one installed.
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79SuperVert
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PostPosted: Mon Oct 25, 2010 11:15 am    Post subject: Reply with quote

This is the pic of the Wolfsburg West muffler installation kit for a 40hp stale air. Can you show me which one you are referring to? It looks like there's only one size gasket ring that would fit over the J tube.

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PostPosted: Mon Oct 25, 2010 11:21 am    Post subject: Reply with quote

79SuperVert wrote:
Never heard of those. This kind?

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[/url]


Yes. I have a complete set but the only one I have ever used is the 13mm. Very useful wrench. Works great for pulling the carb too. Every VW owner should have one.
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Harris
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PostPosted: Mon Oct 25, 2010 11:28 am    Post subject: Tracking Down a Backfire Problem Reply with quote

It's the round gasket that looks like it's made of asbestos.

Joe, if the ones you have fit loose on the J tube, PM me with an address and I'll send you two that fit. Most kits have the larger gasket. The one you need fits tight on the J tube and most kits only include the larger gasket.

Lou
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Erik G
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PostPosted: Mon Oct 25, 2010 12:14 pm    Post subject: Reply with quote

backfiring out of the exhaust, or through the carb? it can be both, and that will tell you where the problem lies
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PostPosted: Mon Oct 25, 2010 12:45 pm    Post subject: Reply with quote

I hope this doesn't sound stupid, but if I only hear it when I'm driving, I don't know how to tell whether it's through the carb or through the exhaust. It kind of sounds too loud to be coming from inside the engine compartment but I don't know if a carb backfire sounds different. Would there be some visual indication around the carb area?

Also, if it only happens during engine braking, would it backfire through the carb? Other than for the backfire it runs great, starts right away, no hesitation, smooth acceleration in all gears, no other indication of a problem.

Thanks for all the replies so far, by the way.
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PostPosted: Mon Oct 25, 2010 12:48 pm    Post subject: Reply with quote

79SuperVert wrote:


The VW shop manual says that backfiring can also be addressed by turning the idle air mixture screw out 1/8 turn. I'm going to try that next.

Are you sure about this?
Backfiring on decell can be caused by exhaust leaks and/or too rich a mixture. I think I would try turning it in 1/8 turn.
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79SuperVert
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PostPosted: Mon Oct 25, 2010 12:50 pm    Post subject: Reply with quote

61SNRF wrote:
79SuperVert wrote:


The VW shop manual says that backfiring can also be addressed by turning the idle air mixture screw out 1/8 turn. I'm going to try that next.

Are you sure about this?
Backfiring on decell can be caused by exhaust leaks and/or too rich a mixture. I think I would try turning it in 1/8 turn.


I will read it again before I actually turn the screw. But also note, it doesn't backfire on deceleration. It only backfires when I brake with the engine. The note in the shop manual specifically refers to turning the screw out when it backfires as the engine brakes the car.
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PostPosted: Mon Oct 25, 2010 12:58 pm    Post subject: Reply with quote

I'm sorry if I wasn't clear, but by "decell" I meant engine braking.
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79SuperVert
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PostPosted: Mon Oct 25, 2010 1:00 pm    Post subject: Reply with quote

61SNRF wrote:
I'm sorry if I wasn't clear, but by "decell" I meant engine braking.


OK. Because if it was also backfiring every time I took my foot off the gas it would be driving me nuts.

And I WILL check the wording in the manual before I turn the screw! It's running fine otherwise and I would like to keep it that way.
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PostPosted: Mon Oct 25, 2010 2:07 pm    Post subject: Reply with quote

I will be interested in hearing about this as I have the same problem with my '62.
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