Brainstorm for My Backfire Problems - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 08-14-2007, 08:57 PM Thread Starter
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Brainstorm for My Backfire Problems

Hello everyone. I just picked up a 1990 VN750 and am having problems with a backfire. After starting the bike with the choke, there is a noticeable backfire every 4 to 5 seconds followed by a pronounced 200 - 300 bump in RPMs and the cycle repeats. The backfire seems to be coming out of the exhaust pipe attached to the aft cylinder. Also, on deceleration there always seems to be two to three smaller backfires. Any thoughts on the culprit?
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post #2 of 6 (permalink) Old 08-14-2007, 09:19 PM
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Do you have stock pipes on, and is the premuffler installed (aka Goatbelly)
It is a large black bulky object connected to the exhaust under the bike in front of the tire.
Coastering or Marbiling is a easy fix.

Chad Falstad "Hawk"
Vroc #17649
2011 HD Ultra Classic "angel"
2001 Nomad 1500 Sold March 2012
2001 VN 750 "Sold June with 2008 with 21,000""Serinity"
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post #3 of 6 (permalink) Old 08-14-2007, 09:44 PM
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Hears what I know,on my 86 the aft cylinder always takes a Little longer to fire than the front when it's cold 200 - 300 bump up when it takes off.That might be your backfire.On mine it doesn't back fire no-more can of seafoam took care of that.It still take longer for the rear to warm up.As for the rest just check out the forums under Engine / Exhaust / Cooling Man let me tell you these guys got my bike running excellent and I never ask a ? allso Carbs and Fuel System

86 Vn 750 30,000 Miles
Stripped of emission
Led Battery monitor
Harley Exhaust
Lubed all over the place
Tool bag and saddle bags
all lights led
Rick's stator
oem r&r
160 thermostat
mf battery
led license plate
Shaved, autozone air breathers (chrome)
404 dunlops
Lots more to do.

Last edited by HotRodPro; 08-14-2007 at 09:48 PM.
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post #4 of 6 (permalink) Old 08-15-2007, 06:34 AM
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Sounds a lot like what mine was doing. I put a half a can of Seafoam in a full tank of fuel, ran it long enough to get the mixture into the carbs and let it sit for 3 days. When I cranked it after letting it sit, it ran like an entirely different bike. It still ran on only one cylinder until about 3000 rpm when the other cylinder would kick in then after about a mile it would run fine. I repeated the procedure and after sitting for a couple of days the bike ran great, both cylinders firing immediately on startup and it doesn't even backfire any more. All this happened after I had paid my local Kawasaki dealer $315.00 to clean my carbs and tune it up for the season. After they tore the carbs apart for the 2nd time and it ran no better this factory certified "technician" said that there was a hole in one of the carbs but he couldn't find it, so I should buy new carbs and maybe that would fix it.
I had never heard of Seafoam before I joined this group and didn't have much faith in any kind of fuel additive to fix a problem like that but I've been convinced. Do a search for "Seafoam" on this forum for a lot of other stories about it. You can find it at Autozone, O'Reilly's and at some Wal Marts.
Hope this helps. At least it won't hurt anything and just might save you a lot of money. Good luck and enjoy your bike.
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post #5 of 6 (permalink) Old 08-15-2007, 07:03 PM
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I agree Seafoam made a believer out of me to.

86 Vn 750 30,000 Miles
Stripped of emission
Led Battery monitor
Harley Exhaust
Lubed all over the place
Tool bag and saddle bags
all lights led
Rick's stator
oem r&r
160 thermostat
mf battery
led license plate
Shaved, autozone air breathers (chrome)
404 dunlops
Lots more to do.
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post #6 of 6 (permalink) Old 08-17-2007, 03:52 PM Thread Starter
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Thanks for the suggestions. I am going to head home today and put my first can of seafoam to use and see if that will fix my problems. I even had the grand idea to give it a try out on my wife's old car. I will let you know if the seafoam does not work the miracle I need.
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