Vacuum operated switch

Reply Subscribe

Thread Tools

Search this Thread

Aug 12, 2018 | 06:30 AM

Bill#

Thread Starter

Stage III

Joined: Aug 2018

Posts: 3

Likes: 0

From: Indiana

Vacuum operated switch

1985 FLHTC. Looking at some of these switch's. They all look the same. But in the description It has 3" HG activation, 5" HG and 6" HG. What is this? Does it make a difference what one is used?

Thanks

Aug 12, 2018 | 08:12 AM

nvbirdman

Tourer

Joined: Mar 2013

Posts: 312

Likes: 25

From: Nevada

Don't know the difference between 3, 5, and 6, but HG is the symbol for mercury. These are mercury switches, not vacuum.

Aug 12, 2018 | 08:31 AM

multihdrdr

Club Member

Joined: Oct 2011

Posts: 11,175

Likes: 2,483

From: Nor Cal

They're Vacuum Switches rated in inches of Hg (inches of Mercury) for activation ... Does this vacuum gauge look familiar?

Last edited by multihdrdr; Aug 12, 2018 at 08:36 AM.

Aug 12, 2018 | 08:31 AM

Toypuller

Seasoned HDF Member

Joined: Feb 2009

Posts: 5,542

Likes: 6,217

From: In your head rent free

Inches of Hg is a term, for the amount of negative pressure, it will take to operate the vacuum switch.

Vacuum is measured in Hg. Maximum is 30. So your switches would take whatever the number correlates too.

Larger the number= more vacuum pressure.

Quote:

Originally Posted by nvbirdman

Don't know the difference between 3, 5, and 6, but HG is the symbol for mercury. These are mercury switches, not vacuum.

Not mercury switches, those take mecury to make an electrical connection, like old style thermostats.
when measuring vacuum, Mercury is the standard of measurement, as in how much negative pressure to pull a column of mercury to a height of a specified number of inches.

Last edited by ChickinOnaChain; Aug 17, 2018 at 03:52 PM. Reason: Multiple posts

Aug 12, 2018 | 08:52 AM

hardheaded

Seasoned HDF Member

Joined: Oct 2012

Posts: 11,226

Likes: 3,049

From: St.Louis Mo.

These vaccum switchs control the spark advance on your bike. Buy the correct one for your application or you may encounter spark knock.

Aug 12, 2018 | 09:08 AM

RDHIGH

Road Master

Joined: Jun 2018

Posts: 760

Likes: 368

From: Winnipeg

Yeah- these vacuum switches (VOES) are used by your ignition to determine load, and advance or retard the timing accordingly. You can order any one you want- if you have a vacuum tool (pistol type vacuum pump with a guage)- you can remove the silicone plug on the voes switch- using a small screwdriver- you can adjust the level of vacuum when the switch activates- then just seal up the switch with new silicone.