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

 

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.

 

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.

 

if its bad will it cause the bike to die while running once engine is hot

 

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.

 

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.

 

Recently bought w/14K miles & SUPER clean. I just had carb bowl off to clean accelerator passage from sitting. Inside the bowl was clean & accelerator was plugged in the outlet on tube in throat & lower passage under bowl. Newer S&S E carb. Runs kinda the same though. It acts like it's too retarded. To ride it you gotta baby the throttle till up to speed. I see under by the battery I see an SENT Ignition. Possibly VOES?

 

PS, flame is not often. It's like you have to coax it to rev. Static timing? I'll check maņana..........