VOES Switch Explained - Harley Davidson Forums

Go Back   Harley Davidson Forums > Harley Davidson Tech & Mechanical Forum > Engine Mechanical Topics
Log In 

Engine Mechanical Topics Discussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.

VOES Switch Explained

Thread Tools Search this Thread
Old 06-28-2005, 01:54 PM
HDF Tech HDF Tech is offline
Join Date: May 2005
Posts: 14,543
Default VOES Switch Explained

What is the Vacuum Operated Electrical Switch (VOES)? What does it do and why is it there?

All Harley Davidson motorcycle carbureted models since the 1984 model year have used the VOES to improve throttle response, increase MPG, and meet EPA requirements for emissions.

The VOES is a motorcycle part described as a vacuum ignition retard device. That is, under low vacuum conditions the switch is open and has no effect on ignition timing. Under high vacuum, the switch closes and advances ignition timing. Essentially, the VOES is like the vacuum advance in older type automotive distributors.

The VOES is a normally open vacuum operated switch that closes under 3-5" of vacuum. The switch is connected to a lead from the ignition module. Under high vacuum, 3-5 inches or higher, the switch closes. A lead from the switch to ground closes a circuit in the ignition module. This circuit advances the timing of the spark. The advance increases throttle response and decrease fuel consumption and emissions.

The vacuum hose is usually connected to a port on the carburetor or intake manifold depending on motorcycle year and carburetor. There are several different VOES switches used the mounting bracket style and operating vacuum being the main differences. The FLHT models have a different vacuum range than the other models. However, just about any VOES can be adapted for use by adjusting the point at which the switch closes.

The point at which the switch closes.

The switches can be adjusted by removing the potted plug and adjusting the setscrew. You will need an accurate vacuum gauge and vacuum hand pump. We have been able to set the operating point as low as 2 inches and as high as 7 inches.

Why would you want a VOES?

We have experimented with converting 1972 and later ignitions from points to electronic ignition. We have used Dyna 'S' conversions for H-D's. We have used Crane, Compufire, Spyke and other Harley Davidson conversion kits. With some of these such as the Dyna 'S', you still have to use the mechanical advance system. This requires service and routine maintenance.

Others work very well having digital advances and provisions for a VOES switch. We experimented with installing a VOES in a 1983 FX and found we have improved throttle response and better mileage. We also routinely install the VOES in custom built Harley Davidsons and even our own Kenny Boyce framed Harley FXR's use VOES with a Crane HI4 module. During Dyno runs, we found that part throttle roll on power was increased as was throttle response.

We believe that most street ridden Harley Davidson motorcycles will benefit from a VOES.

For racing applications or supercharged, turbo-charged or bikes using Nitrous Oxide, we do not recommend using a VOES. This is due to the possibility of a sudden timing change causing a backfire which can be a bad thing under these conditions!

Source: http://www.directparts.com/static/ar...arleyvoes.html

Reply With Quote
Old 08-20-2013, 05:48 PM
rcamp01 rcamp01 is offline
New Member
Join Date: Jul 2008
Posts: 38

Will this keep the engine from peaking its rpms? my engine what's to cut.. out
at high rpms. could it be that it's bad and not advancing ?
Reply With Quote
Old 08-23-2013, 04:37 PM
Harleycruiser's Avatar
Harleycruiser Harleycruiser is offline
Outstanding HDF Member
Join Date: Apr 2012
Location: North Florida
Posts: 2,810

Originally Posted by rcamp01 View Post
Will this keep the engine from peaking its rpms? my engine what's to cut.. out
at high rpms. could it be that it's bad and not advancing ?
What year is your bike, the VOES was replaced with a MAP sensor in the newer bikes. Both retart the ignition, under load. The VOES is a vacuum activated switch the MAP is a manifold absolute pressure sensor.
No neither limits the rpm of the motor, that is the job of the ignition module.
Curvatious Mistress, Play Pen, Project build

Mudding on my Harley Video
Reply With Quote
Old 09-24-2013, 06:22 PM
46u's Avatar
46u 46u is offline
Road Warrior
Join Date: Mar 2011
Location: Macon, GA USA
Posts: 1,378

What a VEOS switch does is advance the timing when there is enough vacum is pulled as the rpm go up. Yes if the VEOS switch is bad can keep it from reveing up and can mess up your motor from running retarded all the time. A quick test to see if it is work at all is disconnected both wires to the VEOS and sucking on the tube and with a ohm meter see if it gets continuity while sucking on it. Now to see if you is kicking in at the right suction you have to have a vacuum pump with a gauge. If the suction is off you and adjust it if you dig all the goop out of the end as there is an adjustment screw under it. Most time the problem is the diaphragm has gone bad in it.

5 more states and I will have them all on one motorcycle
If you see my motorcycle on a trailer call the police it was stolen!
Reply With Quote
Old 04-13-2014, 11:16 PM
BigJames618 BigJames618 is offline
New Member
Join Date: Apr 2014
Location: Belleville, IL
Posts: 6

if its bad will it cause the bike to die while running once engine is hot
Reply With Quote
Old 04-15-2014, 04:17 AM
JustDave13's Avatar
JustDave13 JustDave13 is offline
Road Captain
Join Date: Aug 2013
Location: San Diego North County
Posts: 696

I had my VOES come loose and disconnect from the vacuum hose, there was a lot of spiting/popping and the bike lacked power.
I spotted it after a few minutes of head scratching.

2013 Heritage Softail
Andrews 57h cams
Rush slip on mufflers
Arlen Ness Big Sucker air cleaner
Power Vision tuner
Reply With Quote
Old 05-22-2014, 09:26 AM
Skidpalace's Avatar
Skidpalace Skidpalace is offline
New Member
Join Date: Apr 2014
Location: Waltham MA
Posts: 14

Originally Posted by JustDave13 View Post
I had my VOES come loose and disconnect from the vacuum hose, there was a lot of spiting/popping and the bike lacked power.
I spotted it after a few minutes of head scratching.
That is because your carb had a massive air leak, not because the VOES was malfunctioning. The missing hose was letting air into your manifold. Your VOES was simply not activated and operating in its normal condition of a safe retarded timing.
'97 Softail Custom FXSTC

Corbin Gunfighter, Corbin solo & LePera Bare Bones Solo Biker Gel seats.
CVP carb tune kit with 175 Main and 45 idle
DNA Stage 1 Cone air filter
Screamin' Eagle 2 into 1 (Supertrapp Supermeg)
Reply With Quote
Old 06-08-2014, 03:15 PM
SoftailCustomRider SoftailCustomRider is offline
New Member
Join Date: Jun 2014
Location: Wyoming
Posts: 2
Default VOES Vacuum

When testing with a vacuum pump, Will the switch hold vacuum? mine will not hold and bleeds off. I assume this would cause a vacuum leak.
Reply With Quote

Similar Threads
Thread Thread Starter Forum Replies Last Post
Ignition module problem? Gpsjr10 Ignition/Tuner/ECM/Fuel Injection 2 09-25-2015 01:29 AM
VOES/Coil question tmanbuckhunter Evo Classic Models 94 12-02-2014 04:00 PM
Vacuum switch SportsterSnow Sportster Models 10 07-08-2014 09:11 PM
1993 Softail Heritage dnajna51 Softail Models 1 12-27-2013 06:09 PM

bracket, converting, davidson, electronic, evo, harley, hg, ignition, inches, installation, performance, points, shovelhead, switch, voes

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not 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 Off
Pingbacks are Off
Refbacks are Off

Forum Jump

All times are GMT -5. The time now is 01:49 PM.