Backfire at high rpm on decel - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 07-09-2007, 07:50 PM Thread Starter
 
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Backfire at high rpm on decel

I have noticed that I am getting alot of back firing on decel. How do you find out which side it's coming from or due you adjust both side equaly. I have never had to adjust the carbs and to be honest I don't know how. Any help would be great.
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post #2 of 12 (permalink) Old 07-09-2007, 07:56 PM
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Originally Posted by KENNETH FORTUNE View Post
I have noticed that I am getting alot of back firing on decel. How do you find out which side it's coming from or due you adjust both side equaly. I have never had to adjust the carbs and to be honest I don't know how. Any help would be great.
Probably you want to adjust your air/fuel mixture if you haven't already (now I'm afraid to say whether you're running lean or rich!). The air/fuel screws are on the sides of each carb, just by where the vacuum hose connects. Gently bottom out each screw (i.e., turn it clockwise until you feel a little resistance - then you're at the bottom); most folks enrich the ratio (less air = more fuel) by turning the screws out counterclockwise about 2 1/4 turns. Or thereabouts. Factory setting is 1 5/8ths, which is really, really lean. Word on the street is to not take it out more than 3 turns...

And if you've already messed around with the screws, ignore my reply and hopefully someone will jump in with next steps.

C
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post #3 of 12 (permalink) Old 07-09-2007, 08:02 PM
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After you have done what Cindy suggested, search on "marbling" or "coastering" here in the forum. If you don't mind disabling the reed valves, it will do wonders for stopping the muffler pops.

Jon

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post #4 of 12 (permalink) Old 07-10-2007, 07:52 AM Thread Starter
 
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Probably you want to adjust your air/fuel mixture if you haven't already (now I'm afraid to say whether you're running lean or rich!). The air/fuel screws are on the sides of each carb, just by where the vacuum hose connects. Gently bottom out each screw (i.e., turn it clockwise until you feel a little resistance - then you're at the bottom); most folks enrich the ratio (less air = more fuel) by turning the screws out counterclockwise about 2 1/4 turns. Or thereabouts. Factory setting is 1 5/8ths, which is really, really lean. Word on the street is to not take it out more than 3 turns...

And if you've already messed around with the screws, ignore my reply and hopefully someone will jump in with next steps.
I have not touched the screws. So I will Start their. Thank you
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post #5 of 12 (permalink) Old 07-10-2007, 07:53 AM Thread Starter
 
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After you have done what Cindy suggested, search on "marbling" or "coastering" here in the forum. If you don't mind disabling the reed valves, it will do wonders for stopping the muffler pops.

Jon
What is the purpose of the reed vavles. I will do what it takes to get rid of as much popping as I can.
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post #6 of 12 (permalink) Old 07-10-2007, 08:04 AM
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My decel backfiring ceased completely when I swapped out the stock spark plugs.

EZC

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post #7 of 12 (permalink) Old 07-10-2007, 08:06 AM
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Originally Posted by KENNETH FORTUNE View Post
What is the purpose of the reed vavles. I will do what it takes to get rid of as much popping as I can.
The reed valves are part of your emissions system - the idea is to introduce additional air into the carbs to burn off any unburnt fuel (before it hits your exhaust system and burns there). The popping on decel is - if I'm explaining this right - like little backfires as the fuel gets consumed. The only potential problem with marbling the valves is passing emissions inspection - not sure if you have to go through that or not. If you do, you can pull the marbles before inspection or just avoid marbling altogether and run it stock.

C
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post #8 of 12 (permalink) Old 07-10-2007, 10:34 AM Thread Starter
 
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The reed valves are part of your emissions system - the idea is to introduce additional air into the carbs to burn off any unburnt fuel (before it hits your exhaust system and burns there). The popping on decel is - if I'm explaining this right - like little backfires as the fuel gets consumed. The only potential problem with marbling the valves is passing emissions inspection - not sure if you have to go through that or not. If you do, you can pull the marbles before inspection or just avoid marbling altogether and run it stock.
I'm a car mechanic so I understand the backfiring concept. I also found that my screws were almost out to 3 turns. Backed them all the way in and turn them to 2 1/4 turns. Have not ridden yet to see if any better. I've got new plugs I just was waiting to fix the backfire first. Should I go ahead and replaced them then start my adjustments. Also I live in Virginia and their is no emmission laws yet. But if doing that helps then thats what I'm going to try. Thanks for the help.
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post #9 of 12 (permalink) Old 07-10-2007, 10:46 AM
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Quote:
Originally Posted by KENNETH FORTUNE View Post
I'm a car mechanic so I understand the backfiring concept. I also found that my screws were almost out to 3 turns. Backed them all the way in and turn them to 2 1/4 turns. Have not ridden yet to see if any better. I've got new plugs I just was waiting to fix the backfire first. Should I go ahead and replaced them then start my adjustments. Also I live in Virginia and their is no emmission laws yet. But if doing that helps then thats what I'm going to try. Thanks for the help.
Typically, the screws get turned out to lessen the muffler pops, so you turning them in to 2.25 turns will probably make it worse, not better.

Put our new plugs in and take it for a ride. If popping is still bad, turn the screws out another .25 turn each and see if this helps, if not try another .25 turn.

If still popping, get yourself a couple of marbles.....

Jon

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vn750.com Member # 828

Rick's Stator and R/R
MF AGM Battery
Coastered
Degoated
Shaved & Jetted
Iridium's
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Dunlop D-404's
23,XXX miles and holding pending gasket change (underway!!!)
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post #10 of 12 (permalink) Old 07-10-2007, 11:21 AM
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Ken, if you're getting backfiring on three turns out, maybe you're running too rich a mixture? Like I say, stock set-up is 1 5/8ths so you might want to try somewhere between 1 3/4 and your current 3 to see if that makes any difference (moving 'em a quarter turn at a time). As far as which side is causing the problem...I don't know how to tell you that exactly; if it's not obvious (like your right eardrum explodes), sometimes it's just a "feel." Sorry that's not more helpful - anybody else got an easier way to tell? Can someone riding behind ya see which pipe is backfiring?

C
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