sputter at low speed low rpm - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 33 (permalink) Old 04-03-2012, 12:43 PM Thread Starter
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sputter at low speed low rpm

2003 VN750
In first or second gear at low rpm, or when backing off the throttle I experience what feels like and sounds like engine misfire. There is no loss of power or stalling. Can't tell if it happens at higher speeds/rpm, too noisy.
My mechanic replaced the spark plugs and caps and vacuum tested the carbs. tells me the carbs are balanced and voltages are good.
After I got it back, it still does it, but not as much.
What else could cause the misfire experience (if that's what it is)?
I run high test only and each refill gets Sentry gas treatment.

Sam
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2003 VN750
Purchased 4/27/2010
@ 23813 miles
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post #2 of 33 (permalink) Old 04-03-2012, 12:57 PM
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Try running regular 87 octane, the hi test doesn't improve performance. Some one that knows more will tell you the same thing I'm sure. My 2000 always runs good on the 87.

2000 VN 750
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post #3 of 33 (permalink) Old 04-03-2012, 12:58 PM
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Part of your problem is likely due to running high test gas and sentry gas treatment.

These bikes need to run on Regular gas.

2nd...are you taking about a "popping" from the motor when you close the throttle??

If so.... This is normal. Do a search for "marbling"...

If the motor is in fact "missing" do you smell gas? Does it backfire loudly? If not, it's likely not missing...but the aforementioned de-accell popping due to the reed valve system.

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post #4 of 33 (permalink) Old 04-03-2012, 01:08 PM
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Here's good info from the Versus on the backfiring issue. My next project is removing the emission stuff:

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



Pete Herrmann
1994 Vulcan 750 40K on the clock and counting....

Bought 4/2011 28k Miles,
New Rick's Motorsports R/R
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post #5 of 33 (permalink) Old 04-03-2012, 05:13 PM
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Just a note here the popping on decel also occurs on bikes with out the emissions stuff on board, my 86 UK model does the same and has never had emissions stuff fitted at all.

Last edited by Swagman; 04-03-2012 at 05:19 PM.
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post #6 of 33 (permalink) Old 04-03-2012, 05:16 PM
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Quote:
Originally Posted by Swagman View Post
Just a note here the popping on del also occurs on bikes with out the emissions stuff on board, my 86 UK model does the same and has never had emissions stuff fitted at all.
but not as bad.. i took my emission stuff off, coasted and still have pops, but not as loud.
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post #7 of 33 (permalink) Old 04-03-2012, 05:24 PM
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Quote:
Originally Posted by slimvulcanrider View Post
but not as bad.. i took my emission stuff off, coasted and still have pops, but not as loud.
Yeah I guess it does quite down some as a lot of you guys or most of you have coastered your bikes, but as you say it still pops and if you are knew to the bike you could think something is wrong when there isn't
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post #8 of 33 (permalink) Old 04-03-2012, 05:48 PM
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Here is a thought,as it happen to me last night. I have alot of lights on my bike that I am going to replace with led lights. Check your battery and your charging of the battery. I know last night I ran out of charge on my battery. I run two fog lights that run at 55watts a piece. Luckily I was going down hill when I was giving it throttle,but was dogging. I was also coasting,so was not really charging battery. I turn off the fog lights and then took a little bike the bike started to run fine. The only thing I think is running these lights drain the battery. The spark plugs were getting no power to them. I could be wrong, but that is the way it seemed to me. I found 3 watt replacements for the 55 watts. I also ordered the 6 watt replacement for the 55 watt headlight that is on there now.


2002 Vulcan 750
V&H Pipes
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NGK Iridium Spark Plugs
Green Led Night Lights
Shinko 230 Tour Master Tires

Last edited by Kufbass; 04-03-2012 at 05:54 PM.
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post #9 of 33 (permalink) Old 04-03-2012, 07:53 PM
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Hey Sam, my `91 vn, made for sale in Canada, never had any of the emmission equiptment on it.
Canadian bikes came with the coaster plates installed instead of the fresh air reed valves, but mine still pops and backfires when declerating too.

Many members here have cut the popping way back by pulling the cover or seal off the top of the fuel/air mixture screws and turning them further out, to enrichen the mixture.
I believe the factory setting is about 1 5/8 turns out from closed.
The usual recommended setting to cut back on deceleration popping it between 2 1/2 to 3 1/2 turns out.
Put a little dab of silicone on the threads to keep the screw in place when done adjusting the screw.

Gordon

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

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https://www.vn750.com/forum/11-vn750-general-discussion/9127-top-ten-items-you-would-suggest-new-owner-do-his-new-ride.html
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post #10 of 33 (permalink) Old 04-03-2012, 08:21 PM
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Quote:
Originally Posted by Kufbass View Post
Here is a thought,as it happen to me last night. I have alot of lights on my bike that I am going to replace with led lights. Check your battery and your charging of the battery. I know last night I ran out of charge on my battery. I run two fog lights that run at 55watts a piece. Luckily I was going down hill when I was giving it throttle,but was dogging. I was also coasting,so was not really charging battery. I turn off the fog lights and then took a little bike the bike started to run fine. The only thing I think is running these lights drain the battery. The spark plugs were getting no power to them. I could be wrong, but that is the way it seemed to me. I found 3 watt replacements for the 55 watts. I also ordered the 6 watt replacement for the 55 watt headlight that is on there now.
110 watts is way too much draw for the bike. I don't think the posters problem is electrical ....although yours certainly is. Surprised the bike was rideable... The Vulcan has perhaps 70 watts of available power, and that's at 5000-6000 rpms. Two 55 watt lights will kill your battery. You say a 6 watt replacement? LEDs I assume. I just used 20w halogens.

Even without the "emissions" crap as you call it,the bike can still "pop" when you close the throttle while breaking. This is somewhat due to lean mixture, and response if the CV carbs.... And how "open" the throttle was before you closed it.

For the record, it's not really hurting anything and some folks like me....actually like it.

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