Hard Starting Including Backfiring (Loud Blasts!), But Seems Fine After Starting - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 15 (permalink) Old 12-04-2011, 07:26 AM Thread Starter
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Cool Hard Starting Including Backfiring (Loud Blasts!), But Seems Fine After Starting

When trying to start ours (a 1990) when cold or even when warm and having sat for 20 minutes, it takes a massive amount of cranking to finally get started. Once it starts, it runs good, idles smoothly and has lots of normal power.

Note: Since we are in FL, the bike never sits, and is used very regularly.

Also noticed, was that is seems like the gas tank pressurizes while cranking to try to start. We heard a hissing sound after unsuccessfully trying to start, and found it came from the gas tank fill cap.

Any ideas? Thanks!
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post #2 of 15 (permalink) Old 12-04-2011, 09:50 AM
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In many cases this is the sign of a low battery. Try jumping it with a car battery and see how well it starts. An MF gel battery ussually fixes this problem.

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post #3 of 15 (permalink) Old 12-04-2011, 10:00 AM
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Do Not have the car runing when you jump it, you can fry the electrical system bad.
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post #4 of 15 (permalink) Old 12-04-2011, 11:12 AM Thread Starter
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Quote:
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In many cases this is the sign of a low battery. Try jumping it with a car battery and see how well it starts. An MF gel battery ussually fixes this problem.
Still does it with a battery charger in the "55 AMP Engine Start" mode connected to battery, so it does not appear to be a battery issue.

And besides, we had the battery tested about a week ago, and it passed with flying colors.
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post #5 of 15 (permalink) Old 12-04-2011, 12:05 PM
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Quote:
Originally Posted by Aufgeblassen View Post
Still does it with a battery charger in the "55 AMP Engine Start" mode connected to battery, so it does not appear to be a battery issue.

And besides, we had the battery tested about a week ago, and it passed with flying colors.
Check the plugs and plug wires. When I got my 750 it did this when it had NGK plugs that had been there for 18k miles. I threw the iridium plugs in and she started instantly - no backfires.

This should be your first step before trying anything else unless you are sure your plugs are in perfect order.

Edit: When I said it would do this - It could take a minute to get her started - after assaulting the neighborhood with several blasts that sound like a shotgun going off.

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
TOC MCCTs
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Tuxedo Mod
Rebuilt Forks w/ Progressive Springs
V&H Cruzers
VN750.com Grill Cover
Meanstreak Seat
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R


1990 Kawasaki Vulcan 750

1998 Honda VFR800 FI

2014 Honda VFR800F

1989 Pontiac Firebird Formula 350

Last edited by thtanner; 12-04-2011 at 12:19 PM.
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post #6 of 15 (permalink) Old 12-04-2011, 12:05 PM
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Another reason that I have come across on the back fire, is a little bit of water in the fuel. You can try some water treatment to remove moisture from gas. I use some cheap stuff called "heet." I buy it at Wal-Mart or auto parts stores. Many here like "sea foam."

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post #7 of 15 (permalink) Old 12-04-2011, 01:47 PM
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Try starting the bike with the fuel cap opened. Sounds like you might have a clogged vent.

+1 on checking the plug wires and putting in new iridium plugs.

A full tank of fresh gas with half a can of SeaFoam might be a good idea too...as a bit of crap in a carb can making starting difficult.

Backfires while starting are usually a sign of a weak battery. If your that sure your battery is good (is it an AGM?) it might be a bad wire, a loose ground, a clogged jet, or a clogged gas cap vent.

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post #8 of 15 (permalink) Old 12-04-2011, 03:13 PM Thread Starter
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thtanner: What is an R/R? And you must have got that bike cheeeeep since it was an '86, eh?
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post #9 of 15 (permalink) Old 12-04-2011, 05:27 PM
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Originally Posted by Aufgeblassen View Post
thtanner: What is an R/R? And you must have got that bike cheeeeep since it was an '86, eh?
R/R is the Rectifier/Regulator, which is part of the charging system. I paid $1100 for her and have put about $400 in so far, making it around $1500 total.

She's riding great at the moment! Getting ready to go out here in about 30 minutes..

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
TOC MCCTs
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Tuxedo Mod
Rebuilt Forks w/ Progressive Springs
V&H Cruzers
VN750.com Grill Cover
Meanstreak Seat
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R


1990 Kawasaki Vulcan 750

1998 Honda VFR800 FI

2014 Honda VFR800F

1989 Pontiac Firebird Formula 350
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post #10 of 15 (permalink) Old 12-04-2011, 09:12 PM
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Quote:
Originally Posted by Aufgeblassen View Post
When trying to start ours (a 1990) when cold or even when warm and having sat for 20 minutes, it takes a massive amount of cranking to finally get started. Once it starts, it runs good, idles smoothly and has lots of normal power.

Note: Since we are in FL, the bike never sits, and is used very regularly.

Also noticed, was that is seems like the gas tank pressurizes while cranking to try to start. We heard a hissing sound after unsuccessfully trying to start, and found it came from the gas tank fill cap.
Any ideas? Thanks!
The hissing sound could be a blocked tank vent tube, which leads to a condition we often refer to as POOGS, -the phantom out of gas syndrome. See this link for the cure and prevention:
https://www.vn750.com/forum/showthread.php?t=17572

If new iridium plugs and the other suggestions made still don`t cure the hard starting problem, try fergy`s mod by wiring 12 volts straight to the ignition coils via a relay switch as shown in this link:
https://www.vn750.com/forum/showthread.php?t=17276

There is also a pick-up coil mod for moving them closer to the alternator rotor.
It is reported to help with the hard starting too:
https://www.vn750.com/forum/showthread.php?t=18550

Gordon

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

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July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
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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