RPMs not going down when letting off throttle - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
From the gas tank to the carbs
All fuel system discussion

 
LinkBack Thread Tools Display Modes
post #1 of 6 (permalink) Old 02-07-2011, 10:44 AM Thread Starter
Git-R-Done!
 
AZ Kev's Avatar
 
Join Date: Jan 2011
Location: Phoenix, AZ
Posts: 282
iTrader: (1)
 
RPMs not going down when letting off throttle

Hello all -

To clarify the title - after my bike has warmed up, and I am riding along, if I let off the throttle, instead of the RPMs falling all the way to idle as one might expect they would, they stay where they are for a moment, and start falling very slowly. If I pull the clutch in they fall more, but if I don't, they stay up.

I am thinking it is some kind of carb issue, as most things like this seem to be. Seems I remember reading somewhere that it might be a result of the bike running too rich - does that sound even remotely possible?

As always, any and all suggestions/insights are greatly appreciated


AZ Kev
AZ Kev is offline  
Sponsored Links
Advertisement
 
post #2 of 6 (permalink) Old 02-07-2011, 12:05 PM
Senior Member
 
cglennon's Avatar
 
Join Date: May 2008
Location: Portland, OR
Posts: 734
iTrader: (0)
 
Send a message via Skype™ to cglennon
If the bike is running fine, except for this issue, then perhaps it is something minor.
  1. Broken or weak return spring
  2. Sticky accel and decel cable (when was the last time you lubed them?)
  3. Sticky carb/throttle pivot points

The above can be check by simple observation.


Chris Glennon - Portland, OR
cglennon is offline  
post #3 of 6 (permalink) Old 02-07-2011, 12:18 PM
Members who have donated towards server costs
 
flitecontrol's Avatar
 
Join Date: Dec 2008
Location: Monroe, LA
Posts: 4,699
iTrader: (14)
 
If the tach is working properly, the RPMs are going to indicate how fast the crankshaft is turning. With no throttle, and the clutch lever not pulled, the tach should wind down as motor or other braking takes effect. Haven't paid much attention to this as I'm not watching the tach due to whatever reason I let off the throttle (approaching cage at intersection, upcoming turn, etc.).

What you are describing sounds normal to me.

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
_____________________________________________
"Black Beauty"
1989 VN750 acquired December, 2008, 6,711 miles
Currently 23,298 miles

Old Blue
2001 Honda CMX250 Rebel acquired July, 2008

1987 VN750 project bike, acquired August, 2009, 33,000 miles and balancer sticking out of the case, currently awaiting attention and parts
flitecontrol is offline  
 
post #4 of 6 (permalink) Old 02-07-2011, 12:23 PM
Senior Member
 
n2omike's Avatar
 
Join Date: Oct 2010
Location: Spencer, WV
Posts: 232
iTrader: (0)
 
If the cables are fine and the throttle is closing, you have a vacuum leak.

05 VN750
Iridium Plugs
Spline Lubed front/rear
ignition pickups gapped
AGM Battery
Relocated MOSFET R/R
Coaster Mod
Pilot Screws at 2-1/4 turns
Slipstreamer S-08 Windshield
F&S Saddlebags/Mounts
Luggage Rack
12V Outlet
Mustang Seat
sissy bar
Oversized Pirelli Front Tire
6k miles

PW50, XR50, TTR90, XR100, DT175 (2-smoker), CRF230F, XR250R (dual sported), XR400R 4 KIDS, LOL!

1966 mustang street/strip
4-speed, nitrous
[email protected] 135.6
n2omike is offline  
post #5 of 6 (permalink) Old 02-07-2011, 03:05 PM Thread Starter
Git-R-Done!
 
AZ Kev's Avatar
 
Join Date: Jan 2011
Location: Phoenix, AZ
Posts: 282
iTrader: (1)
 
Great suggestions

Thanks all - those are some great suggestions, and I plan to go through all of them in a process of elimination to figure it out. I am glad to hear that - from what it sounds like - is probably not something major.

I did notice a bit of a hissing sound... I am wondering exaclty where I might check for vacuum leaks - any tips?

Once again thanks

AZ Kev
AZ Kev is offline  
post #6 of 6 (permalink) Old 02-07-2011, 05:57 PM
Old Fart
 
Knifemaker's Avatar
 
Join Date: Jun 2004
Location: Catawissa, MO
Posts: 11,644
iTrader: (4)
     
Garage
Your discription was not that clear...am guessing you mean the engine rpms do not fall when you let go of the throttle...when the bike is in neutral or the clutch lever is pulled in.

OR

If you are moving and in gear...and let go of the throttle...... engine speed will slowly go down...dependant on vehicle speed. So you need to clarify more here.

If the former is true..

Actually a slow to fall throttle (while out of gear) is usually caused by an air leak...making a lean mixture not a rich one.

Check the tightness of the clamps on the intake boots and the ones between the cylnder and the carb. next check the small hoses off the carb.

One way to check of leaks is to spray WD 40 on the suspected area while the motor is running. If the exhaust smoke turns white..you have a leak.


Now... if you mean the bike is moving and in gear...you need to use the brakes to see the engine speed go down


KM

Sometimes it helps to re-set the idle after the motor has warmed up...(to roughly 1100 rpm)

If You Are Not Sure If I Am Joking or Not....I AM !!Photos:
http://www.flickr.com/photos/knifemaker1954/sets/

Last edited by Knifemaker; 02-07-2011 at 06:00 PM.
Knifemaker 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