popping/ backfiring - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 06-01-2011, 10:20 PM Thread Starter
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popping/ backfiring

Hi everyone after a lot of reading in here and some of the posts are the same but I have somethings to add.
I have a 1993 with 58000 kms on it, Which I just bought last week. All is good with the bike start very good, accelerates good shift fine. But when I let off the throttle all the way it backfires/popping only on the right side.
It has a new battery too.
This bike has fishtail exhaust pipes on it with non removable baffles in pipes, so when I read the post no 1 said much about what kind of pipes they had.
When I was looking at it I asked if they had it re-jetted and they said that they bought it from someone else so as what I think they never had it re-jetted, I am thinking on it is from not getting it re-jetted but wanted to ask in here before I go this way.
I looked on the carbs and saw that they tried to set the factory settings on the jets never tried to adjust the screws wanted more info first.
A person thought it might be from the lack of back pressure so I tried a big washer in front of the baffles only on the side it back fires it took about 80% of it away but still thinking on re-jetting too.
Any info would be helpful.
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post #2 of 9 (permalink) Old 06-01-2011, 10:46 PM
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Welcome to the Vulcan madness

You need to coaster/marble the reed valves, and turn the fuel/air adjustment screw out on the backfiring cylinder, to richen the mix when decelerating.
Read this for an explanation and follow the directions:
https://www.vn750.com/forum/showthread.php?t=1081

Ask if anything isn`t clear.

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/11-vn750-general-discussion/9127-top-ten-items-you-would-suggest-new-owner-do-his-new-ride.html

Last edited by OlHossCanada; 06-01-2011 at 10:52 PM.
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post #3 of 9 (permalink) Old 06-02-2011, 11:21 AM Thread Starter
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Hi thanks for posting a reply and will try this before taking it to a dealer to get carbs done. But wondering any pictures to show where the right hose is for marbling ?
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post #4 of 9 (permalink) Old 06-02-2011, 12:32 PM
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Quote:
Originally Posted by scubadiver View Post
Hi thanks for posting a reply and will try this before taking it to a dealer to get carbs done. But wondering any pictures to show where the right hose is for marbling ?
http://jr_allas.tripod.com/documents/Ear_Removal.htm
Look at the 4th picture down, "Both Carbs Removed".

At the front of the front cylinder head, behind the throttle cables, there is a rectangular steel plate ("coaster") about 2 1/2" X 3" held on by two small bolts. It will be behind the air filter housing (ear) on your bike. That coaster replaces the reed valve with the hose that you want to marble. The other one is exposed out in the open on the left side of the rear cylinder head. You can see the rear coaster on the second to last picture in the series.

I`ll see if I can find a pic with the reed valves and hose in place.

Ok here it is.

Scroll down to the 6th picture in the opening post to see the left side reed valve with the hose going around behind the rear cylinder head.
:https://www.vn750.com/forum/showthread.php?t=10466

the 7th picture shows the front reed valve.

(Just noticed that when jt got this basket case, the rear valve cover with the heat shield was installed on the front head.)

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; 06-02-2011 at 03:59 PM. Reason: add link
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post #5 of 9 (permalink) Old 06-02-2011, 04:15 PM
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Question Poping on decelleratiion

Is this really normal? I figured it was part of the bike and there was no harm being done. If it doesn't bother a person there is no real bennifit to worring about it is there?

Just want to know

Mcneuby
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post #6 of 9 (permalink) Old 06-21-2011, 01:15 PM Thread Starter
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hi everyone after taking my bike in to see about the popping /backfiring at a Kawasaki dealer they found out why it was doing this. He found that the diaphragm in the 1 carb was nothing left so the popping from the carb cause of the popping only on the 1 side but they replaced both. hope to pick up the bike today. I'll post more after.
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post #7 of 9 (permalink) Old 06-21-2011, 01:38 PM
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Quote:
Originally Posted by scubadiver View Post
hi everyone after taking my bike in to see about the popping /backfiring at a Kawasaki dealer they found out why it was doing this. He found that the diaphragm in the 1 carb was nothing left so the popping from the carb cause of the popping only on the 1 side but they replaced both. hope to pick up the bike today. I'll post more after.
im just wondering if the "stealership" will have your "old damaged ones" ready to show you !!!. just a thought. i dont trust dealersips one bit !.
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post #8 of 9 (permalink) Old 06-21-2011, 11:50 PM
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im just wondering if the "stealership" will have your "old damaged ones" ready to show you !!!. just a thought. i dont trust dealersips one bit !.
I agree with you but if the bike was sitting for a bit then it possible that the rubber in the carb got dry rotter from either water in carb from the gas and will do this on occasions. Its not common but not unlikely... I would have guessed dirty jets but would have found out when pulling the carbs apart myself. I always pull the carbs apart when I buy a motorcycle from someone else for the shear reason of neglect. Even if i can see through the holes of the jets, i always clean them with a cutting torch tip cleaner because they are small enough to not only clean the holes but bore them out a tad.
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post #9 of 9 (permalink) Old 06-24-2011, 04:33 PM Thread Starter
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Hi just wanted to updated you all about my carbs when I got to the dealer to talk more about the carbs they wanted to clean them and look in to it more but after talking to them and all they told me the carbs were pretty clean and very well stored off driving months but the diaphragm was almost nothing left in the 1 carb but replaced both just to make sure and some o-rings and re-jetted mid-range jet they wanted to re-jet main jet but it is on back order till the end of July. So I want to ride more than wanting it in shop but after i got it back all popping/ backfiring was gone. So I will trust the dealer that I took it to for more work on it if needed.
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