Misfire & Backfire - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Engine / Exhaust / Cooling
\ From the radiator, through the case and out
the exhaust. If it has to do with the cooling,
engine or exhaust, discuss it here!

LinkBack Thread Tools Display Modes
post #1 of 9 (permalink) Old 08-26-2008, 11:31 PM Thread Starter
Join Date: Aug 2008
Posts: 48
iTrader: (0)
Misfire & Backfire

Hi guys,

I'm new here and new to vulcans. I just got a '93 VN750. I really enjoy the bike and riding, but it has two small problems. The bike doesn't want to idle until the engine is fully up to operating temperature and it is hesitates like it has a misfire problem. Today one cylinder totally cut out so the bike was just running/driving on the other cylinder. After the bike got up to operating temperature both cylinders were working/firing. The bike was sitting out in the rain for only 5 to 10 minutes the night before.

It seems now and then the battery is having a hard time cranking the engine starter. The battery is just three days old and was fully charged before installation.

And besides this "dead cylinder" that came back to life; the engine always feels like it has no spark on one cylinder or spark coil. This is causing the engine to backfire and sputter some.

Ideas of what it can be?

Some things of what i think it may be:
bad spark plug wire/s,
fouled spark plug/s,
airbox is not sealed airtight,
battery cables corroded or worn out,
bad or corroded electrical ground,
short circuit in the wire harness somewhere,
bad ignition coil,
vacuum leak near carbs,
stator not working correctly.
VSB is offline  
Sponsored Links
post #2 of 9 (permalink) Old 08-27-2008, 12:44 PM
Calif Rider
weh44att's Avatar
Join Date: Jan 2006
Location: Petaluma Calif
Posts: 725
iTrader: (0)
Is the battery a lead acid or MF battery? Mf batteries give you more cranking power on cold starts. How good is the battery charging, check voltage. Try cleaning up all your electrical connections. How do the spark plugs look when you pull them. Everything you mentioned could be the cause of the cylinder cutting out.

2004 25,500 miles
Led tail light enhancement
Homemade floor boards
Headlight modulator
Extra heat sink on R+R
R+R relocation
Homemade driver's backrest
Fused Stator
Mcct conversion-cost 4.50
Ride-on in tires
crash bar with home made hyway pegs
iridium plugs
home made fork wind deflectors
coil pickups adjusted.
Kenda kruz tires 110/90 170/80
weh44att is offline  
post #3 of 9 (permalink) Old 10-09-2008, 01:10 PM
Junior Member
Join Date: Aug 2008
Posts: 2
iTrader: (0)
I've got something similar on my "new" '92, the front cylinder cuts in/out.
Rode in to work today on one cyl, hope it starts OK tonight like that...

The plugs were clean last time I checked, but I can smell raw gas at stoplights and the backfiring is definitely in the right exhaust only. So that narrows it down to (most likely) a front spark issue.

If you can narrow down the possibilities to front/back, fuel/nofuel, you'll probably git 'er fixed faster.
Good luck.
unclephil is offline  
post #4 of 9 (permalink) Old 10-09-2008, 01:29 PM
and the Adventure Cycle
hyperbuzzin's Avatar
Join Date: Jun 2004
Location: Western PA
Posts: 6,138
iTrader: (1)
Once again, try Seafoam. It's available at many auto part stores and many Wal-marts are now carrying it.

Could also be the carbs need some attention (cleaned/check for bad hoses)
Neither of ya mention how many miles are on your bikes or what kind of general condition they're in.

AKA: Tim & 'The Adventure Cycle' VROC #24567, NEVROC, SteelCity VROC

"When life throws you curves,
Aim for the apex."

Author Unknown
hyperbuzzin is offline  
post #5 of 9 (permalink) Old 10-09-2008, 02:18 PM
Join Date: May 2008
Location: northeast pa
Posts: 881
iTrader: (1)
2x on the seafoam, that may be the place to start. some have had battery issues that made the bike run bad. maby you can check the battery with a multimeter or you can take the bike to autozone where they will check it for free. good luck

dutter is offline  
post #6 of 9 (permalink) Old 10-09-2008, 04:17 PM
Once Banned
cegodsey's Avatar
Join Date: Jun 2006
Location: Bryant, Arkansas
Posts: 2,125
iTrader: (0)
As with the rest of the gang, make sure it is a Maintenance Free battery (it doesn't have anywhere to add water). All the parts stores (including walmart) show that a wet cell battery will fit our bikes, but in reality, they may only work for a couple of weeks at the most. You'll need a Maintenance Free (MF), also called an AGM battery.

Assuming that it's not the battery, it could very well be your charging system.

As to the misfiring, you'll probably need to clean the carbs. I'd try doing a search in the box above for gumout, and review the procedure to "backwash" the crud out. Here's the link: http://vn750.com/forum/showthread.php?t=8345
If that doesn't work, you may need to pull the carbs. Personally, I'd recommend letting the shop do it, unless you are REAL HANDY with mechanical stuff.

BUT, before trying the gumout and carb cleaning, try the SeaFoam as per HyperBuzzin. There's nothing like it, so don't use just any gas treatment. Add about an ounce per gallon. You can get it at most auto parts stores, it looks like this:

Run through a tank with it, and see if it helps.

2000 A16
Drilled baffles
$65 leather saddle bags
Kuryaken grips
relocated R/R
25,000+ original owner miles

Last edited by cegodsey; 10-09-2008 at 04:21 PM.
cegodsey is offline  
post #7 of 9 (permalink) Old 10-09-2008, 05:11 PM
Old Truck Junkie
niterider's Avatar
Join Date: Jul 2007
Location: Roby Texas
Posts: 4,130
iTrader: (15)
Usually when back fire is mention along with rain or washing the bike. In many cases it is water in the fuel. drain both carbs and add some kind of water remover in the tank and try it again.

02 honda sabre 1100
niterider is offline  
post #8 of 9 (permalink) Old 10-09-2008, 07:50 PM
Members who have donated towards server costs
Sky Rider's Avatar
Join Date: Jun 2006
Location: Corpus Christi, Texas
Posts: 1,647
iTrader: (0)
If the bikes sat for a long time before you acquired them, you could have a lot of crud in the carb bowls. Seafoam treatments have worked for most but if that doesn't work, pulling and cleaning the carbs is in order. It doesn't take much to clog one of the very small jets in the carb. One quick fix which has worked for me it to take a 4mm allen wrench and drain the carb bowls. You'd be surprised how much gunk comes out with the gas. Once the bowls are drained, close the drain plugs and restart the bike. It may help get rid of what ever crud is blocking the jets. This trick has worked for me.

If the bike is misfiring and you can smell raw fuel, it's a carb problem. If the cylinder is cutting out in a certain speed range, it could be an ignition problem but it could also be a carb problem with a clogged or missing jet. I had the high speed jet come completely out of its mount and drop to the bottom of the carb bowl which made the rear cylinder stop running at anything over 3k RPM.

Jim W
93 VN 750 "Ursula"
Moved R/R 08Sep06
R/R rewire 17Feb07
New R/R, Installed 14Jun08
New Stator installed 10 Jun08
Maintenance Free Battery 12Jan08
21480 Miles
VROC #8542
Sky Rider is offline  
post #9 of 9 (permalink) Old 10-09-2008, 09:35 PM
BSkaggs513's Avatar
Join Date: Feb 2006
Location: Ohio, Dayton-Cincy area
Posts: 421
iTrader: (0)
I agree with the Seafoam suggestion. I had similar issues with another bike that was just a crudded carb. Also- chase the ground connections on your battery to the frame and then the frame to the engine. Remove the screws and clean the terminals where they contact. A dirty ground will prevent charging and make the bike slow to turn over. Sandpaper is good for the cleaning.

Good luck!

SW Ohio

'02 VN750
Pipes drilled
Spline lubed
R/R relocated
AGM batteried
Iridium equipped
LED tail lighted
8000-ish miled
Soon to be MCCTed

Lovin Life.
BSkaggs513 is offline  
Sponsored Links


Quick Reply

Register Now

In order to be able to post messages on the Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

Once registered, your User Name"cannot be changed". We can make exceptions within 7 days, but after that, it is set in stone.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome