Boxerworks.com

Since I've been using this site, the wealth of information and general camaraderie here makes coming to the forum and asking questions nearly irresistible.

I have a question about vacuum gauges. I know about making a manometer with a yard stick and automatic transmission fluid, but, what about making a meter using vacuum gauges? Is there any special type of vacuum gauge or is it just a simple gauge like the ones found at McMaster Carr http://www.mcmaster.com/#vacuum-gauges/=e5905v

The idea, and I'm sure I'm not the first to think of it, is the gauges make it possible to make changes under load because they would be easier to carry. Dialing in the cable take off would be easier, (in theory) and they would be easier to stow away. I am a cheap SOB and handy so I'd rather make something myself if I can instead of buying it. Sometimes, (often), it is over my head but I like to try.

The big isues with mechanical (or digital) gauges are, will THEY stay in sync over time, and they usually need to be damped in some way so that they can be read. Damping is usually easy, just restrict the vacume hose in some way.

Makeing sure that both gauges read the same a year or two from now is the trick. You can hook them up to a tee to make sure, but if you find them in error most cheap gauges have no method for adjustment.

I've always thought it would be good to measure vacuum balance on the road I was thinking of a Magnahelic differential gauge which would have the desired sensitivity but they are seriously expensive and also maybe too fragile. If you were thinking of two vacuum gauges measuring absolute pressure they would have to be the old fashioned 0 - 30" Hg gauges that were once commonly used for engine diagnostics. They would certainly be informative but I wonder if they would have enough sensitivity to do an accurate balance. 1" Hg on the dial would be the equivalent of (without doing an accurate calc) approx. 17" on your average 4$ manometer.

how does the twin max work?

twist wrote:how does the twin max work?

It has a sensor that tells you the difference between the pressure on either side of the sensor. It can't tell you what the pressure is, only the difference between the two. It is very sensitive, which is good, and that sensitivity is adjustable, which is also good, but the biggest advantage I find with it is its ability to be set into a tank bag to measure balance under load (while riding, usually up a hill for me). This is very useful getting the throttle bodies on my early Oilhead perfectly synced (the bike is overly sensitive to perfect throttle body sync).

The three disadvantages of the twinmax are price, only works on twins, and doesn't tell you actual vacuum pressure.

Major Softie wrote:

twist wrote:how does the twin max work?

It has a sensor that tells you the difference between the pressure on either side of the sensor. It can't tell you what the pressure is, only the difference between the two. It is very sensitive, which is good, and that sensitivity is adjustable, which is also good, but the biggest advantage I find with it is its ability to be set into a tank bag to measure balance under load (while riding, usually up a hill for me). This is very useful getting the throttle bodies on my early Oilhead perfectly synced (the bike is overly sensitive to perfect throttle body sync).

The three disadvantages of the twinmax are price, only works on twins, and doesn't tell you actual vacuum pressure.

That would be handy for balancing only. It would be nice to be able to see where your carbs are while running down the road. Of course knowing the vacuum reading can be quite helpful for adjusting mixture. I always try to tune the idle mixture so that I get the highest vacuum reading I can on each cylinder (slides or butterflies barely open). I then fine tune by ear to get the smoothest sound.