Hesitation (Carb Tuning?) - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
VN750 General Discussion

 
LinkBack Thread Tools Display Modes
post #1 of 7 (permalink) Old 05-10-2010, 09:23 PM Thread Starter
Junior Member
 
Join Date: Apr 2010
Posts: 17
iTrader: (0)
 
Hesitation (Carb Tuning?)

My '92 VN750 is having a problem with hesitation/stumbling around 5,000 RPM. I notice it only in that particular RPM range. It strumbles a lot when cruising at highway speeds, but seems to get better if I choke the carb. I also get some backfiring when I shift gears at that RPM. I don't notice it anywhere else in the RPM range.

So, I am thinking it is running lean. I have already run 1 tank of seafom through, currently working on the second tank.

Should I richen the carb with the screws? Do the carbs have adjustable needles? What should I try first? I was thinking that since it only seems bad at the one point, the needle might help.

Anyone have a suggestion? Thanks
nearma12 is offline  
Sponsored Links
Advertisement
 
post #2 of 7 (permalink) Old 05-10-2010, 10:30 PM
On His Lady Vulcan
 
wkrizan's Avatar
 
Join Date: Apr 2008
Location: Washington State
Posts: 1,647
iTrader: (10)
 
These carbs do have ajustable pilots yes, one for each carb. If youre running completely stock intake and exhaust and you have lead plugs where your pilot screws are located then you just might have another issue. If you dont have all of the above ie. aftermarket exhaust, earshave, no lead plugs on each of your pilot screws then I'd start messing with them. Need further info to really be of any help.

"You came out of your mom looking like SHlT. She thought you were beautiful. Don't know what scared me most, your looks or her judgment."











Pictures of the "Ladies"
wkrizan is offline  
post #3 of 7 (permalink) Old 05-11-2010, 05:16 PM Thread Starter
Junior Member
 
Join Date: Apr 2010
Posts: 17
iTrader: (0)
 
Everything I stock as far as I know. I have only had the bike for a month or so, so I have not torn into anything yet.

I see the adjustment screws on the side of the carbs, but isn't that only good for low speed? Or am I wrong?

I have worked on lots of carbs from single cylinder bikes before, so I have a pretty good understanding of how they work. Usually they have a pilot jet, main jet, jet needle, and airscrew that can all be changed/adjusted.

As I said before, I only feel the hesitation at 5,000 RPM. I don't feel it above or below that range. So, that leads me to believe that if I change anything I would need to richen the needle position. Main jet seems fine since over 5,000 seems to run good. Pilot seems fine as idle and low RPM performance is good. On my other bikes, the airscrew only effects the lower speed performance.

So, since I am not familiar with the VN750 carbs, I need some advice from someone who is. Could this be a synch problem? If I need to give any more information let me know. Thanks!!
nearma12 is offline  
 
post #4 of 7 (permalink) Old 05-11-2010, 05:54 PM
Junior Member
 
Join Date: Apr 2010
Location: Norman, OK
Posts: 21
iTrader: (0)
 
I am having the same problem and I have a loose spark plug boot and cap. I have new ones on the way... might see if you have something loose down there.
86blackrigid is offline  
post #5 of 7 (permalink) Old 05-11-2010, 05:59 PM
On His Lady Vulcan
 
wkrizan's Avatar
 
Join Date: Apr 2008
Location: Washington State
Posts: 1,647
iTrader: (10)
 
I believe the air screws affect low and mid range. It seems to me that with a completely stock intake and exhaust system that your issue shouldnt be with a stock needle. Have you check to see if you happen to have a tear in your diaphragm or coaster enricher?

EDIT: 86 above has got a good point there, I'd check that as well, as for a carb sync, build yourself a manometer and give that a shot as well.

"You came out of your mom looking like SHlT. She thought you were beautiful. Don't know what scared me most, your looks or her judgment."











Pictures of the "Ladies"

Last edited by wkrizan; 05-11-2010 at 06:05 PM.
wkrizan is offline  
post #6 of 7 (permalink) Old 05-14-2010, 04:37 PM
Undercover Sportbiker
 
AJCruzin's Avatar
 
Join Date: Oct 2007
Location: SoCal (SF Valley) 91343
Posts: 1,097
iTrader: (19)
 
Assuming nothing else is wrong (IE spark plugs good, no loose boots etc.) then you probably have the "Kawi midrange stumble" issue. Some, not all, but SOME carb'd Kawi bikes, even in stock form, stumble a bit in the transition from slow jet to main jet. Shimming the needles is about the best way to resolve the problem.

AJCruzin is offline  
post #7 of 7 (permalink) Old 05-17-2010, 01:06 PM
Bandito
 
Mellow's Avatar
 
Join Date: Sep 2009
Location: Salisbury, MD
Posts: 160
iTrader: (1)
 
Cant the vacuum line running to the right ear if it is not in correctly make the same kind of issues?

1993 Vulcan 750 - SOLD
---------------------------
1996 Suzuki Bandit 600 - Current ride
Mellow is offline  
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

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

Password:


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

Email Address:
OR

Log-in










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