Hard to start... with sound effects - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 08-27-2011, 08:52 AM Thread Starter
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Hard to start... with sound effects


My 1990 VN750 - 12,500 miles - has been a terrific bike (aside from the twice yearly POOGS event), but recently has been hard to start. After a couple of tries there's a backfire, it starts, and then it's a little rough until it warms up. Seems to be getting progressively worse. Any ideas what to look for? -Harlan
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post #2 of 9 (permalink) Old 08-27-2011, 12:06 PM
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This is typical of some vn's. Possible causes are: Weak battery (replace with AGM), pick up coil gap (adjust to .020 or .018), condition of starter motor (rebuild), connections and grounds (clean and grease), dirty fuel system (use Seafoam or ChemTool) & air cleaners, weak ignition coil voltage (check) due to 12v power feed.

Every bike has some gremlin, ours is the hard or hot start problem. Overall, it's a fun bike to ride and is worth the effort to tweak.

BTW, I've had a backfire that has set off car alarms! always fun!

95 VN750 (eBay)31k+
GL1100 front fender
OEM engine guard
OEM high back rest
'V-Twin' HWY pegs
Black 750 Spectre handlebars
SunPro Volt Meter (Amazon)
Maier bug shield (JCW)
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Emgo air filters
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post #3 of 9 (permalink) Old 08-27-2011, 01:14 PM
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I'd lean to the easy/cheap things first. Seafoam the carbs, it'll be your best friend.

87 vn750at least that is what the frame #'s say
"Squirrel Bike" aka Jersey

Rat bike with a good PR agent

shaved and coastered
2 into 1 exhaust
rear 170 and front 110
Relocated R/R
custom dash with voltmeter
Spitfire windscreen
Plutonium plugs
Recovered seat without "butt hammers"
More to come
Praise to the Parts Goddess Crobins for needed things

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post #4 of 9 (permalink) Old 08-27-2011, 05:22 PM
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Originally Posted by Harlan View Post
.. (aside from the twice yearly POOGS event) ...
In my case the gas tank vent tube was rubbing against the rear tire. The result was a fine rubber power that was continually sucked into the gas cap vent causing POOGS. I relocated the gas tank vent tube and flush it well to get all the rubber powder out.

Chris Glennon - Portland, OR
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post #5 of 9 (permalink) Old 08-28-2011, 12:24 PM
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A good battery goes far to cure starting problems but have you put in iridium plugs? They are fantastic.

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post #6 of 9 (permalink) Old 08-28-2011, 01:06 PM
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Originally Posted by Gemguy View Post
A good battery goes far to cure starting problems but have you put in iridium plugs? They are fantastic.
The NGK Iridium DPR7EIX-9 plugs are the ones you want.


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

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15

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post #7 of 9 (permalink) Old 08-29-2011, 04:09 PM Thread Starter
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Thank you, gentlemen.

I have a (relatively) new gel battery in there, but I will check the grounds, the fuel, and get some new NGKs straightaway. Appreciate the input!
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post #8 of 9 (permalink) Old 08-29-2011, 06:27 PM
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Harlan, it is pretty easy to check the voltage to the coils via the coil power wire. On a 90, it is possible that the wiring is getting a little weak going to them. Follow the instructions in my sig to check them.

The iridium plugs are definitely something you need to invest in. Seafoam is cheap insurance on the fuel system. Most of us give her a monthly drink of seafoam in the fuel tank, just for preventive maintenance. If she runs a little rough until warmed up, you might have a little gunk blocking your pilot jets. The seafoam might clear that up. If your plugs are fouled, it will be harder to start and cause the rough warm up time too.
Grounds and weak or corroded connections certainly can cause weak spark and poor running too. If you clean up connections/grounds, wipe some dielectric grease on them before slapping back together to prevent the corrosion.
Have fun getting it all figured out and holler back and let us know how you're doing.

Kyle, TX VN750.com member #707 VROC#19556
2002 VN1500 Classic
Spline Lube Procedure, with photos, R/R Relocation and Coil Mod
Rusty Tank Cleaning!
Electrical Fault Finding Flowchart

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post #9 of 9 (permalink) Old 08-30-2011, 12:57 PM
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Seems like the other guys have the basic recommendations covered.

From the title, I was expecting some sort of "Car Talk"-esque attempt to duplicate the sound...gotta say, I'm a little disappointed.
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