When is a 750 a 375? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 70 (permalink) Old 05-28-2014, 02:15 PM Thread Starter
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When is a 750 a 375?

So last night, I rode from work about 30 miles on the freeway doing an average of 70mph and then stopped at a grocery store to get some dinner. When I came out of the store, and cranked the bike up, it sounded weird, and sounded like only one cylinder was firing... I rode it about a half mile down the road to meet with some guys, and it had definitely turned into a 375cc! No good!

I don't know what happened since it had run perfectly from work to the store... I checked the spark plug wires, holding them up to the plug, and could see (and feel) plenty of spark from both of them... I checked the exhaust, and the front one is high pressure and hot, while the back one is lower pressure and cool air... no gas smell...

When I try to ride it, it obviously struggles to accelerate because of only one jug firing, but it also backfires like crazy... I'd have thought it's because of the fuel dumping into the rear exhaust and exploding, but that doesn't make sense since the rear exhaust is cool...

I "limped" it home about 5 miles or so, but didn't do any more diagnostics last night...

I posted this in the carbs/fuel section because I'm suspecting it's a carb issue, but wanted to see what y'all thought before I did anymore troubleshooting...

Thanks!

Matt

------------------------------
GloryRider
Atlanta, GA
Current Ride: 1995 Vulcan 88 (1500A9)
Purchased Dec. 2014
approx. 6,800 miles

Previous Bike: 2000 VN750 "Glory"
With homemade stator
Details on stator build here

"Four wheels move the body. Two wheels move the soul"

"You live more in 5 minutes on a bike like this going flat out than some people live in their lifetime." - Burt Munro
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post #2 of 70 (permalink) Old 05-28-2014, 02:19 PM
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Well, isn't that an odd one. When you pulled the plugs did you see any wetness on the plugs in the cyl not firing? i.e. unburnt fuel? Was the spark the same color/intensity for both cyls?

I'd check all vacuum connections, and the carb boots. If you have a sync tool maybe see if they're severely out of sync?

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 #3 of 70 (permalink) Old 05-28-2014, 02:25 PM Thread Starter
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I didn't actually pull the plugs yet... I just pulled the wires off to check for spark thinking the ignition coil might have gone out... The spark intensity was the same for both cyls, yes.

The vacuum connections are solid, and carb boots are on tight with no (apparent) leaks...

It's odd that it happened so suddenly! I mean, it was running perfectly, and then all of a sudden the rear cyl just quit workin!

I'm wondering if there's some piece of crap that got into the jet in the rear carb or something... maybe I should try Wolfie's blowback technique... I don't know how it could, since I have new fuel lines with filters on both of them... I guess it wouldn't take much to clog it though...

Hmm...

------------------------------
GloryRider
Atlanta, GA
Current Ride: 1995 Vulcan 88 (1500A9)
Purchased Dec. 2014
approx. 6,800 miles

Previous Bike: 2000 VN750 "Glory"
With homemade stator
Details on stator build here

"Four wheels move the body. Two wheels move the soul"

"You live more in 5 minutes on a bike like this going flat out than some people live in their lifetime." - Burt Munro
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post #4 of 70 (permalink) Old 05-28-2014, 02:35 PM
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The blowback is worth a shot. Quick and easy, with good recorded results.

I'd pull the plugs and make sure they're not wet. Would definitely narrow down if fuel was getting to them (even though you did not smell gas).

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 #5 of 70 (permalink) Old 05-28-2014, 03:04 PM
..have a vulcan good day!
 
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Quote:
Originally Posted by thtanner View Post
The blowback is worth a shot. Quick and easy, with good recorded results.

I'd pull the plugs and make sure they're not wet. Would definitely narrow down if fuel was getting to them (even though you did not smell gas).
x2 this is key here .....an absolute !
(Fuel or Electronic? )



'86 VN750 13,700 mi -Stock
-Purchased 2008 w/8800mi
Replaced ALL Cables . Kuryakyn LED Voltmeter
SilverStar Ultra 9003/HB2 H4 Headlamp, Jardine Fwd Controls,
Iridiums DPR7EIX-9 & Wires, Tuxedo Mod, Coil Mod, P/U Sensor Mod, Fork Seals,
Splines Lubed - 11/4/2012 - MF AGM Battery
Additional Flashing LED Brake Light on Trunk
Dampers went out @ 13+K !
After TOC MCCT's..... so amazingly quiet I discovered a rattling heat shield on my stock exhaust !
...have a vulcan good day!

Last edited by WilliamTech; 05-28-2014 at 04:54 PM.
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post #6 of 70 (permalink) Old 05-28-2014, 03:14 PM
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I would take the inline fuel filters out and fix the reason I thought I needed them.
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post #7 of 70 (permalink) Old 05-28-2014, 03:16 PM
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That is a good note, why do you have in-line filters? It's not something I'd run, personally.

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 #8 of 70 (permalink) Old 05-28-2014, 03:18 PM Thread Starter
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Honestly, they were there from the previous owner... I just left them on as additional protection from anything in the tank getting into the carbs...

------------------------------
GloryRider
Atlanta, GA
Current Ride: 1995 Vulcan 88 (1500A9)
Purchased Dec. 2014
approx. 6,800 miles

Previous Bike: 2000 VN750 "Glory"
With homemade stator
Details on stator build here

"Four wheels move the body. Two wheels move the soul"

"You live more in 5 minutes on a bike like this going flat out than some people live in their lifetime." - Burt Munro
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post #9 of 70 (permalink) Old 05-28-2014, 03:19 PM
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Quote:
Originally Posted by GloryRider View Post
Honestly, they were there from the previous owner... I just left them on as additional protection from anything in the tank getting into the carbs...
Pull the plugs, if they're dry.. remove the in-line filters and see if it solves the issue.

Seeing as its a vacuum based fuel system, and not pumped, filters can cause flow issues.

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
thtanner is offline  
post #10 of 70 (permalink) Old 05-28-2014, 03:43 PM Thread Starter
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I'll give that a try tonight... thanks!

------------------------------
GloryRider
Atlanta, GA
Current Ride: 1995 Vulcan 88 (1500A9)
Purchased Dec. 2014
approx. 6,800 miles

Previous Bike: 2000 VN750 "Glory"
With homemade stator
Details on stator build here

"Four wheels move the body. Two wheels move the soul"

"You live more in 5 minutes on a bike like this going flat out than some people live in their lifetime." - Burt Munro
GloryRider is offline  
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