Accelerator circuit massage

Tips and Recommendations from Guru Mike Nixon

Moderator: Whiskerfish

Post Reply
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Accelerator circuit massage

#1

Post by mikenixon »

Image

On the GL1100, Honda did something very needful. They added an accelerator pump to the carburetors. Together with smaller throats, these two changes made a huge improvement over the GL1000's carb set, tuning the GL1100's carbs much closer to the way the motorcycle was actually being ridden.

The GL1100's carburetors are of a family Keihin called "VB", a designation which you can see cast into the side of each carburetor body, and a family of carbs Honda used on most of their bikes during the early 1980s. And excepting some Euro and other variations, all of the VB series carbs used during this time have accelerator pump circuits. This includes the six-cylinder CBX, the DOHC inline fours, the 650 four, the 500 and 650 and 400 twins, and even the FT500 single. All have this same accelerator pump system.

It's a good system, the accelerator pump, but it has a fault. Its discharge orifice is so tiny it clogs easily. Coupled with a very low pressure operating diaphragm, it's a cinch most GL1100s are not benefitting from all the throttle response they should be due to a weak accelerator pump system.

Here's how I fix that. I usually try heat first. More than half the time however it isn't enough. I have a piece of a guitar string clamped in a pin vise, which is just a handle to hold very small drills. The pin vise is extended with a piece of welding rod for better reach. After opening both the throttle and choke plates, or sometimes even removing them, I shoot a flashlight down the carb throat and at the same time ease this special tool down to the accelerator pump's upright nozzle. Once in the nozzle's discharge orifice, I rotate the tool to auger the nozzle, which dislodges any varnish or rust (usually both). I'll remove the tool and test the nozzle with an brake cleaner aerosol, and if needed, repeat with the tool. After trying hydraulic methods, heat, and more, this technique has become the one I always use, when needed, on all of the carburetors I rebuild.
User avatar
Track T 2411
Honored Life Member
Honored Life Member
Posts: 8482
Joined: Thu May 29, 2008 9:37 pm
My Album: http://www.ngwclub.com/gallery/v/wingmans/Track+T+2411/
Location: Prairie du Sac Wisconsin

Re: Accelerator circuit massage

#2

Post by Track T 2411 »

Good to know that I wasn't doing a 'bad' thing when I used a wire brush bristle clamped into a small hemostat when I found one plugged on my last build, lol!
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Re: Accelerator circuit massage

#3

Post by mikenixon »

Good man! The accelerator pump is pretty important, isn't it?
User avatar
Track T 2411
Honored Life Member
Honored Life Member
Posts: 8482
Joined: Thu May 29, 2008 9:37 pm
My Album: http://www.ngwclub.com/gallery/v/wingmans/Track+T+2411/
Location: Prairie du Sac Wisconsin

Re: Accelerator circuit massage

#4

Post by Track T 2411 »

Certainly makes a difference compared to the off idle issues of my '76...
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Re: Accelerator circuit massage

#5

Post by mikenixon »

Track T 2411 wrote:Certainly makes a difference compared to the off idle issues of my '76...
I have a video for you to look at...

https://youtu.be/CDnzwDWhN24
User avatar
Track T 2411
Honored Life Member
Honored Life Member
Posts: 8482
Joined: Thu May 29, 2008 9:37 pm
My Album: http://www.ngwclub.com/gallery/v/wingmans/Track+T+2411/
Location: Prairie du Sac Wisconsin

Re: Accelerator circuit massage

#6

Post by Track T 2411 »

Thanks for the video tease, lol! I was hoping for a comprehensive 'how- to. (I know, I'm needy, lol) My question is how do I get my '76 there?
User avatar
pidjones
SUPER BIKER!!!!
SUPER BIKER!!!!
Posts: 3237
Joined: Wed May 22, 2013 4:06 pm
Location: East TN

Re: Accelerator circuit massage

#7

Post by pidjones »

A high "E" in a pin vise is exactly what I used for the accelerator jets in the '79 CB750F that I rescued last year. That's a tiny hole, a long way off, though! The other tool needed is perseverance!
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Re: Accelerator circuit massage

#8

Post by mikenixon »

pidjones wrote:A high "E" in a pin vise is exactly what I used for the accelerator jets in the '79 CB750F that I rescued last year. That's a tiny hole, a long way off, though! The other tool needed is perseverance!
Yes it does. But it is effective, and I do it a lot also.

I know a fellow that removes accelerator pump system discharge nozzles in attempts to clean them, but I have considered that little too much. They can't be cleaned any differently out of the casting than in, and after removing one on a junk carb for practice, I don't like the method.
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Re: Accelerator circuit massage

#9

Post by mikenixon »

Track T 2411 wrote:Thanks for the video tease, lol! I was hoping for a comprehensive 'how- to. (I know, I'm needy, lol) My question is how do I get my '76 there?
Lot of massaging. Ignition maintenance that goes beyond what most folks are willing to do, and carburetor massaging and tweaking that likewise could be described as epic. I have been doing both for as long as I can remember.
Post Reply
  • Similar Topics
    Replies
    Views
    Last post

Return to “Mike Nixon's Spot”