Another Homemade Vacuum Sync'er

[audijunky]

I have made one of these for two cylinders though. It works, but the oil does bounce up and down. I read somewhere else on here that if you put some kind of air chamber(bigger than plastic tube such as 2" PVC) between carb boots and oil in line with the tubing it will stabilize the suction from the engine and make it easier to sync.

[81xsproject]

Yes, when it comes to gauges you have to have some sort of plenum or restrictor to stabilize the vacuum pulses. However, it doesn't take much. I started with a plenum that was at least 2 liters and have down sized to around a half liter and it is still too much.

[mason79]

i made mine with a single gauge and a largish plenum, why do they sell the 4 gauge setup with no plenum?

[dwain61]

Not sure if that's what you want

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

Are you sure that is what you want to happen??

[Ken Talbot]

Originally posted by audijunky
I have made one of these for two cylinders though. It works, but the oil does bounce up and down. I read somewhere else on here that if you put some kind of air chamber(bigger than plastic tube such as 2" PVC) between carb boots and oil in line with the tubing it will stabilize the suction from the engine and make it easier to sync.

You can achieve good dampening by inserting a small plastic plug, with a very small hole drilled through it, into the attachment end of each of the lines. When I bought my mercury sticks, the plugs came with it for exactly this purpose.

[skids]

I have not gone through the Bernoilli equations, Ken, but with the differences in vacuum at the tops of the columns, if there were no contributions due to the weight of the columns, there would definately be continual movement of oil into cylinder with the most vacuum. slurp!

Originally posted by 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.

[skids]

I do think I know what you are saying however, Ken. The difference between the oil gages and the regular configured mercury gages is that the oil gages are not relative to atmosphere as a zero datum, they instead measure differences between the cylinders.

[81xsproject]

This is interesting... This, or one like it, came up on kzr and raised a lot of controversy.

[Hired_Goon]

Originally posted by skids
The difference between the oil gages and the regular configured mercury gages is that the oil gages are not relative to atmosphere as a zero datum, they instead measure differences between the cylinders.

Bingo.

I have been using a setup similar to the first pic for years now. IMO it is far more accurate than vacuum guages. They have the restrictor to compensate the flicking caused by valves. If you screw one restrictor tighter than the others it surely must affect the reading.

I use mine unrestricted and without chambers. Once you get then lined up it is simple to compare the "bounce" in all four cylinders.

My bike, Tuned by the homemade, idles very smoothly down to about 700 rpm. Not possible unless they are spot on.

The dangers of the oil filled tube?

Always keep your hand near the kill switch for the first time. They are a pig to use if your carbs are badly set. It will quickly suck up oil into one tube and fill the lot with air bubbles.

Hydro lock? Not really an issue as with the correct tubing you only have a few milliliters of oil. It will vaporise before doing anything worse than lubing the bores.

I'm very happy with my $5 manometer and wouldn't bother buying anything different.

[Ken Talbot]

Bernouli equations? Yikes! It's been way too long since high school physics class to remember what the heck that was all about, but it does ring a very faint bell. Now I'm going to have to make one of these oil-filled units, complete with an appropriately-drilled dampener, to see just how it compares to a set of mercury sticks. All this talk about relativity and datums has got me fired up...

[81xsproject]

Well, I got my unit built today. All I need to do now is put in what ever fluid I will be using. Should get to try it out some time this week.

[633wrench]

vacume gauges

i recently made a set of gauges using 4 vacume gauges hose,
and valves i bought at a pet store in the aquirium section of the store they were dirt cheap and they stop the needles on the gauges from bouncing!
cheers,
633wrench

[81xsproject]

A gauge and valves is the set up I have now. I think this will be more accurate, will report this week