Backfire on Deceleration - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 15 (permalink) Old 05-05-2008, 05:20 AM Thread Starter
 
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Backfire on Deceleration

I have a 97' vn750. As far as I can tell everything is stock.

When i let go of the gas, it backfires quite a bit, not really loud backfiring, but popping sounds. It does this quite a bit more when I'm decelerating. All though, it still does do it when the bike is not in motion. while the bike is just sitting idle, it is a rare thing to have a backfire.

My service manual says this could be three things broken vacuum switch valve, air suction valve, or the coasting enricher.

I popped off the little coasting enricher cover on the right side of the bike, and found a spring, and a tiny piston, along with a small hole in the cover that I removed. Its all very clean, and there is nothing i can see to be adjusted in there.

As far as the other two possibilities according to my manuel, i have not checked at all yet just becasue i dont have means to test a vaccum, or a possibly part. But does anyone have any suggestions or advice for stopping the backfiring?

This is my first post, and i think you should all know i'm very new to motorcycles! This is my third bike, and I haven't even been riding 9 months yet. Ive never taken carbs apart before, and i'm afraid thats whats going to be required of me for this problem. =)
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post #2 of 15 (permalink) Old 05-05-2008, 05:31 AM
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Hey, welcome to the group! Before you start taking stuff apart, I'd suggest a little research around here first, starting with this-

https://www.vn750.com/forum/showthread.php?t=1083

It's not an uncommon problem, and it's not hard to fix....

Once again welcome!
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post #3 of 15 (permalink) Old 05-05-2008, 08:22 AM Thread Starter
 
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Thank you =)

I looked at that link and found lots of possibilities.

It says that its most likely a fuel air/mixture issue, which is what i was looking for when i opened up the coasting enrichers. However, i found nothing in there that is adjustible. That link says "Back your carburetor mixture screws to about 2 1/2 turns" Is another word for carb mixer screws possibly pilot screws? I'm thinking that there the screws that the coasting enricher "tail" is nearly pointing too about an inch away.. I can only find one diagram in the manual under carb assembly that labels it a "pilot screw plug hole."

That must be what I was looking for, ill try turning them tomorrow.
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post #4 of 15 (permalink) Old 05-05-2008, 08:55 AM
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Backfiring on decel is just part of the vn750 lore. You'll learn to love it!

97 VN 750
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https://www.vn750.com/forum/showthread.php?t=5385
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post #5 of 15 (permalink) Old 05-05-2008, 09:07 AM
 
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eventually you just learn to ignore it, or be the jerk like me who has to travel a tunnel very day and let her backfire in the tunnel. It will turn some heads.
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post #6 of 15 (permalink) Old 05-05-2008, 10:52 AM
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Research Marbleing and or Coastering on this site. Your answer and solution will be found within. Cheers

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post #7 of 15 (permalink) Old 05-05-2008, 01:05 PM
 
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Three things:
1. Marbleing or coastering can fix your problem.
2. Adjusting pilot screws can fix your problem (they are covered with lead cap)
3. Exhaust leaks can cause your problem.

As far as learning to live with it, you don't have to. Personally I hated it when I got my 750, and resolved the issue quickly by coastering. You can find all the info you need here to perform the recommended adjustments.
Goodluck.
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post #8 of 15 (permalink) Old 05-05-2008, 03:40 PM
 
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Talking

Quote:
Originally Posted by KENNETH FORTUNE View Post
eventually you just learn to ignore it, or be the jerk like me who has to travel a tunnel very day and let her backfire in the tunnel. It will turn some heads.
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post #9 of 15 (permalink) Old 05-05-2008, 04:43 PM
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I had an old chevy with a 350 4bolt that I had built and tuned with dual glass packs. I loved the popping on decel in her but kinda not on the bike. After I marbled the kaw the popping quit and only have an occasional back fire at around 55 on decel and a little rumble in first gear going down the hill of my drive way out of the apts., not bad at all. I also only have my screws turned out to 2 turns.

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post #10 of 15 (permalink) Old 05-05-2008, 06:24 PM Thread Starter
 
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Thanks for all the help everyone. After reading about marbleing and coastering, i do actually think that this has been done to my bike. On the rear cylinder towards the top, on the left side of the bike, there is a 3/4 inch hose that runs down under the seat, and it is sealed off there, as well as the place it looks like it connects. Ill have to look at the other cylinder to see if its the same deal, but i think it is actually under the tank.

Edit: Nvm it looks as though each carb takes in fuel in a different place. What that other rubber hose is is beyond me, but ill just leave it alone for now =)

Last edited by Bodaciousbrian; 05-05-2008 at 10:01 PM. Reason: edit
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