Can't stop the backfiring! - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 16 (permalink) Old 04-06-2011, 01:21 PM Thread Starter
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Can't stop the backfiring!

O.K. So I marbled it, replaced the exhaust gaskets with the H/D ones, and have the screws turned out 3 1/4 on the left, and 3 on the right, and it still backfires like crazy! Am I missing something?
It sounds like the left side is the worst. How far out can I turn thoses screws out?
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post #2 of 16 (permalink) Old 04-06-2011, 02:32 PM
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Quote:
Originally Posted by Puddles View Post
O.K. So I marbled it, replaced the exhaust gaskets with the H/D ones, and have the screws turned out 3 1/4 on the left, and 3 on the right, and it still backfires like crazy! Am I missing something?
It sounds like the left side is the worst. How far out can I turn thoses screws out?
Sounds like you still have an air leak somewhere.

Typically the fuel/air adjustment screws have about 5 full turns of threads before they fall out. (Confirm this figure on your carb.)
So you have a maximum of ~3 1/2 turns out for adjustment.
Lock the adjustment with a bit of silicone sealant on the threads so they don`t fall out.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
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post #3 of 16 (permalink) Old 04-06-2011, 02:59 PM
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Didn't someone say the HD gaskets didn't fit well and recommended the OEM ones? Could that be the problem?

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
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post #4 of 16 (permalink) Old 04-06-2011, 03:17 PM
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Not 100% sure, but I think you can also get the backfires if the carb boots aren't properly seating/sealing/closing around the carb. Might want to check them.

I also did the marbling and I couldn't get the backfiring to stop... I suspect the carb boots cause I know I didn't install them right and you can tell by looking at them that air could pass through... however, I hate the air box so much that I don't even want to look at it, so I'm not taking out the carbs until I get the filters for the ear shave so I can take out that damned air box
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post #5 of 16 (permalink) Old 04-06-2011, 03:53 PM Thread Starter
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Thanks guys. I'll recheck all that stuff.
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post #6 of 16 (permalink) Old 04-06-2011, 04:56 PM
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Quote:
Originally Posted by flitecontrol View Post
Didn't someone say the HD gaskets didn't fit well and recommended the OEM ones? Could that be the problem?
The H-D gaskets were recommended a long time ago, then someone said they were smaller in diameter, harder to keep in position while installing, and had a tendency to leak.

Since then I have been of the opinion that Ma Kaw`s exhaust gaskets are the ones to use on Kaw motorcycles. This is not based on any personal experiences, only on reading what others have said. Someone recommended the H-D crush gaskets again a few days ago. I didn`t want to be contrary, with no real evidence of my own, so let it pass to see how they worked out.

It is not clear at this point if the H-D gaskets are the cause of the continuing backfiring, or if it is something else. The jury is still out on the gaskets I guess.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/showthread.php?t=9127
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post #7 of 16 (permalink) Old 04-06-2011, 07:38 PM Thread Starter
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I pulled the left side pipe off and the new gasket looked like it didn't seat right. Think I'll just get the kawi gaskets insted. Also ordered coaster plates today. I'll let ya know how everything works out.
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post #8 of 16 (permalink) Old 04-06-2011, 08:10 PM
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If the carb boots were not seated I think the bike wouldn't idle right

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post #9 of 16 (permalink) Old 04-06-2011, 08:32 PM
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curious, what do a pair of exhaust gaskets run?

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post #10 of 16 (permalink) Old 04-06-2011, 09:43 PM
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Quote:
Originally Posted by carolesteven View Post
curious, what do a pair of exhaust gaskets run?
$3.93 each here at OEM Parts:
http://www.indyoem.com/fiche_section...1991&fveh=9040
Shipping on orders up to $100 costs $10 in USA.

or $6.14 each at Bike Bandit
Orders under $20 ship for $6.95 in USA

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/showthread.php?t=9127

Last edited by OlHossCanada; 04-06-2011 at 09:57 PM.
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