Major Backfire! - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 11 (permalink) Old 07-24-2012, 12:49 PM Thread Starter
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Major Backfire!

My bike runs well, but on occasion it after a ride when I go to start it again it will seem to flood out and then a major backfire. It will start after that, but it is pretty embarassing.

I also apparently need to look into how my carbs are vented because at highway speed the bike tends to sputter, but only when the wind is blowing a certain direction. I have read a few posts on this, but haven't tried anything yet. I do want to get all the bugs worked out because I am going on my first long trip in a few months.

Thanks,
Scott
86 750, 6,200 miles



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post #2 of 11 (permalink) Old 07-24-2012, 01:09 PM
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I also apparently need to look into how my carbs are vented because at highway speed the bike tends to sputter, but only when the wind is blowing a certain direction.
Make sure the vent hose behind the right ear (air filter) is plugged into one of the slotted holes. What you described here sounds like the issue that a dangling hose will cause. Also, if the hose did come out, you should go ahead and cut the end at a 45 degree angle so it won't bottom out.

Also as far as the backfire, I had my bike do that once when the hose fell out of the ear too. Never had it happen again after that was fixed.
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post #3 of 11 (permalink) Old 07-24-2012, 01:15 PM
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I may be wrong, but backfire usually means a lean mixture....happens with POOGS sometimes or if you run the carbs dry.

Check your tank venting system.
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post #4 of 11 (permalink) Old 07-24-2012, 01:23 PM
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Back fires like that also come from weak or low battery. Since we get spark at both power stroke and exhaust stroke some times a low voltage will not ignite at compression but it will on the exhaust stroke.

02 honda sabre 1100
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post #5 of 11 (permalink) Old 07-24-2012, 02:16 PM Thread Starter
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Thanks for the tips. Last night it "went off" and sounded like a shotgun being fired in the neighborhood. I'll check it out over the next few days. I had a friend of mine rebuild the carbs about a year ago, and he removed all of the smog stuff, put in plates to cover the emissions outlet and installed K&N air filters. I have no idea what he did with the vent tubes...The battery is only a year old, but I'll check on that too.



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post #6 of 11 (permalink) Old 07-24-2012, 02:49 PM
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if the battery is a wet cell type...get rid of it and replace it with a AGM maintenance free battery. The VN750 needs a good voltage source to start and run well.

A weak battery can...and does cause backfire on starts.

thanks niterider for the reminder!
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post #7 of 11 (permalink) Old 07-24-2012, 03:26 PM
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My bike did the same thing and when I finally changed the plugs (I replaced mine with the iridium plugs) and it stopped doing this. Plus it started much easier too.


1986 VN 750
20,000 miles
MF Battery
Replaced Stock Turn signals
Starter Clutch
NGK plugs
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Seafoam
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post #8 of 11 (permalink) Old 07-25-2012, 01:16 AM
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Another possibility is after you shut it off, and start it again, and you get a backfire, that sometimes will indicate raw fuel in the cylinder and or exhaust pipe igniting and causing the backfiring.
If at all possible after running it, pull a plug and see if it's wet or dry. A wet plug indicates fuel in the cylinder. A dry plug indicates no raw fuel.
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post #9 of 11 (permalink) Old 08-02-2012, 10:14 PM
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Quote:
Originally Posted by niterider View Post
Back fires like that also come from weak or low battery. Since we get spark at both power stroke and exhaust stroke some times a low voltage will not ignite at compression but it will on the exhaust stroke.
I agree with Niterider on this one.... I was having having backfire issues at startup and all of the classic symptoms of "POOGS". I ran Seafoam through a couple of tanks of gas but saw no improvement.... (except that my fuel guage started working again) Checked the plug gaps and they were fine. So I decided to check some electrical connections under the seat for possible corrosion. What I found almost made me soil myself. There was enough corrosion on the positive battery post to cover it. After cleaning the whole mess up, I bought a new Deka AGM battery (American Made) at Advanced Auto for around $73.00. Before installing, it got a charge on the Battery Tender... Old "Trigger" never started better since I bought her back in 1989. And I haven't had any "POOGS" symptoms since. It's true!! A weak battery can cause all kinds of headaches that can make you think that it's fuel related. "Now if I can just use some of that Seafoam to get my tach working again".... Hmm. Lol!!

Terry

87 VN750 A3
"Trigger"

Black with Silver on tank
Willie & Max saddle bags
Silver Star head lamp
Engine guard
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New Stator - Spring 2008
New relocated R/R - Spring 2008
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post #10 of 11 (permalink) Old 08-02-2012, 10:33 PM
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Check your tachs ground and the connection to the front coil. Thanx for the vote of confidence. lol

02 honda sabre 1100
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