Another Homemade Vacuum Sync'er

[81xsproject]

I found this on another site and thought I'd post it here.

[mason79]

nice, mercury?

[81xsproject]

no, it is oil. You can mix with kerosene for better visibility.

[mason79]

then why can't they use oil instead of the hard to get mercury? on the mercury stix

[Ken Talbot]

On this version, all four channels are connected to a common manifold, and the system is sealed. As one carb pulls a bit more vacuum, it draws one channel up, but the others in effect pull it back down.

On a mercury unit each channel is sitting in an open reservoir, so the vacuum is pulling the weight of a column of mercury. It is only the weight of the mercury column that prevents it getting sucked into the carb (unless you are running without a restrictor, and if you suddenly chop the throttle at high speed.

If you happened to try this unit with one channel unplugged, it would suck the oil into a carb in an instant.

This is a very interesting unit, and it could no doubt be built with the channels much closer and with a more sophisticated manifold across the bottom. That would make it more compact, like the mercury units.

[BLUEJEEPLAB]

Always wondered how the Synchonizers worked, now I know. Old Dogs can learn new tricks.

I happened on an aid for synching the carbs this winter, quite by very unfortunate accident. I grabbed the wrong gas can for my new 2 stroke snowblower and got exactly two blowings out of it before I siezed it (The Chainsaw Can is now sporting a very large "PM" in its side). Anyhow, after I sadly decided that it was beyond economic repair, I looked at the little plastic tank that held the offending gas and realized that it was perfect as a gravity tank for tank off carb tuning, it even has a little strap for hanging and holds about a quart of gas. It is the only remaining reminder of my stupidity.

[skids]

Because it works by difference AND it needs the weight of the column to work, you can imagine that if you have a 2 inch difference showing a regular mercury stick unit (one cylinder to the next), you will show about 2 feet of difference of oil. (that is if mercury has an s.g. of 10 and oil has an s.g. of 0.85). The good part is that if the engine sucks it in, you don't create an extreamly hazardous atmosphere!

Originally posted by Ken Talbot
SOME SNIPPAGE
On a mercury unit each channel is sitting in an open reservoir, so the vacuum is pulling the weight of a column of mercury. It is only the weight of the mercury column that prevents it getting sucked into the carb (unless you are running without a restrictor, and if you suddenly chop the throttle at high speed.

If you happened to try this unit with one channel unplugged, it would suck the oil into a carb in an instant.

[randy]

The good part is that if the engine sucks it in, you don't create an extreamly hazardous atmosphere!

Yeah, but the bad part is if the engine sucks it in, you could have hydrostatic lock and wind up with a bent connecting rod!

[prometheus578]

"Not for me, Papa!"

It is the only remaining reminder of my stupidity.

I've written this little episode down in the file I keep on everybody.
I'll help you remember it from time to time...

[81xsproject]

as was briefly mentioned, another advantage is accuracy. Because of the large difference in weight between oil and mercury, very small height differences in the mercury would show as drastic height differences in the oil.

[Ken Talbot]

But, with this homemade unit, you're not really dealing with the weight of the column of oil because of the 'closed loop' configuration. I have never built one to try, but I don't think the variations would necessarily be that much more than in a set of open reservoir mercury sticks.

[81xsproject]

touche!!

[BLUEJEEPLAB]

Prom,

I've written this little episode down in the file I keep on everybody.

Great, now maybe SWMBO will quit doing it...

[mason79]

then vacuum gauges would be the most accurate right?

[DiverRay]

The mercury stix are the easiest to use, IMHO. I use mine about 3 or 4 times a year, and it's just set all the lines. Vacume gauges, you have to try and set all the needles the same, as they are bouncing.