Topic: Carb sync frequency

[MJL]

The other other thing I've researched is how to build a simple manometer or pressure diff gauge from a long loop of clear hose filled with fluid, such as transmission fluid.  Each end of the loop is connected to a carb vacuum lead and the looped hose with fluid would show the relative vacuum difference between the two systems.  (This arrangement is what airhead beemers apparently homebrewed for their carb syncing.)  As long as the difference in vacuum isn't too great, the fluid would stay in the loop rather than getting sucked into the engine.  Only problem is, we have four, not two carbs to synchronize.  So, I was thinking...why not join two loops of hose together with a manifold arrangement at the bottom of the loop where the fluid would reside, and then all four ends would balance their vacuum difference with fluid heights.  Any thoughts...or shall I be the guinea pig.

There was a 5 or 6 page thread on this a while back, well worth the read.

[eldar]

My mercury tool sorta did that but nothing got sucked out. I have been thinking about getting vacuum gauges and using those. Probably no cheaper but should work just as good.

[ev0lve]

I was reading that vacuum gauges (especially the cheapo ebay types) were pretty tweaky/bounce. Not having used any is that true generally?

[eldar]

Hard to say. I suppose some are but after dealing with a mercury gauge, I doubt they are any worse.

[markjenn]

The other other thing I've researched is how to build a simple manometer or pressure diff gauge from a long loop of clear hose filled with fluid, such as transmission fluid.  Each end of the loop is connected to a carb vacuum lead and the looped hose with fluid would show the relative vacuum difference between the two systems.

The loop may provide some damping, but ultimately it's the height of the fluid column over the reservoir of fluid that you need to measure and the reason mercury is used is because it is a heavy liquid resulting in shorter heights.  Build a manometer with transmission fluid and the height of the tubes has to be much longer, typically 6' or so. It will certainly work fine and if you have a cheap source of tubing and lumber and don't mind a bulky Rube Goldberg contraption in your shop, go for it.  For me, it's just not worth the hassle when there is a relatively inexpensive and welll-made solution available.

- Mark

[feliz]

I made one of the home made manometers, it cost less than $5.00 and workslike a charm. I actually prefer it over my Morgantune for my twin cylinder bikes, I find the fluid doesn't jump around and I hang it off the ceiling of my garage making it real easy to see. Storage is easy I just coil up the empty tubing.

[HondanutRider]

The other other thing I've researched is how to build a simple manometer or pressure diff gauge from a long loop of clear hose filled with fluid, such as transmission fluid.  Each end of the loop is connected to a carb vacuum lead and the looped hose with fluid would show the relative vacuum difference between the two systems.

The loop may provide some damping, but ultimately it's the height of the fluid column over the reservoir of fluid that you need to measure and the reason mercury is used is because it is a heavy liquid resulting in shorter heights.  Build a manometer with transmission fluid and the height of the tubes has to be much longer, typically 6' or so. It will certainly work fine and if you have a cheap source of tubing and lumber and don't mind a bulky Rube Goldberg contraption in your shop, go for it.  For me, it's just not worth the hassle when there is a relatively inexpensive and welll-made solution available.

- Mark

I don't believe the column(s) of fluid would be that high.  What I'm thinking is a column height that would be based on the relative difference in pressure between carburetor vacuums.  That difference of vacuum shouldn't be very significant, and in fact is being tuned/synced to zero.  If, as in a regular manometer, the pressure was relative to atmosphere (open end for positive) or pure vacuum of liquid (closed end for negative), then yes, the column heights would be very unwieldy, especially with a fluid much lighter than mercury.

BTW the spec for carburetor vacuum on the CB350F is listed by Honda to be 16-24 cm of mercury which would work out to be about 7-11 feet of water.  Having never seen carburetor syncing, I would have to theorize that the difference in pressure between two running carbs should be no more than 4-6 cm of mercury, which in a loop of water column should be 2-3 feet. Transmission fluid is a little lighter than water, but not much, so these dimensions for water would still be close for that fluid.  That's still pretty long column (3 feet) that would have to be accommodated, and then even more to allow for bounce or the pulse fluctuations of a breathing engine - however, not entirely unreasonable for a home-brew.  Can someone comment on how much pressure differences they have seen in actual syncing?

[crazypj]

If you blip on the throttle it will easily go to 40~50 cm/Hg when its closed suddenly.
Possible to suck all the mercury out of  gauges (very bad idea , not nice stuff to be breathing after it gets through engine)
Its why I prefer my Honda dial type gauges, you can also do a few test that are not really possible with 'wet' gauges
 I was pretty sure there shouldn't be bleed holes/adjuster screws on the Motion-Pro set up, your supposed to be drawing against a closed container. (but I've never seen/used them except in pictures)
 Morgan works well although I've only ever used them once so can't comment on longevity
Cheap dial gauges work OK but wear out real quick in a shop environment, we averaged about 4~6 months per set. (your mileage may vary  )
 You fit a pilot jet into the tubes to restrict 'bounce' on needles or use thin wall rubber tube as it flexes with vacuum pulses, or, you can ge aquarium clamps to restrict tubes (the clamps that go onto aerators)
Friend in work was in navy, working on carriers when they still used some piston engined planes, he said they dropped 3"~4" pipe into the ocean and would draw 28 ft of water, blew a few engines if pilot/mechanic  'blipped' throttles too quick
PJ

[OldSchool_IsCool]

The trouble with vacuum differential is that the carbs are not under vacuum at the same time.  Vacuum only occurs when the intake valve opens.  That's why the liquid within the tube needs to be tall and/or highly viscus and/or damped pretty heavily.  That's also why the needles of a vacuum gauge like to jump around so much when not dampened.

[markjenn]

All I can say is that I've tried three methods - water manometer, mercury manometer, and morgan - and while all three will work fine, the morgan is just so much easier.  And when the job is done, it slips into its 3"x5"x12" case and gets tucked neatly into my toolbox.

- Mark

[ev0lve]

If you blip on the throttle it will easily go to 40~50 cm/Hg when its closed suddenly.
Possible to suck all the mercury out of  gauges (very bad idea , not nice stuff to be breathing after it gets through engine)
Its why I prefer my Honda dial type gauges, you can also do a few test that are not really possible with 'wet' gauges
 I was pretty sure there shouldn't be bleed holes/adjuster screws on the Motion-Pro set up, your supposed to be drawing against a closed container. (but I've never seen/used them except in pictures)
 Morgan works well although I've only ever used them once so can't comment on longevity
Cheap dial gauges work OK but wear out real quick in a shop environment, we averaged about 4~6 months per set. (your mileage may vary  )
 You fit a pilot jet into the tubes to restrict 'bounce' on needles or use thin wall rubber tube as it flexes with vacuum pulses, or, you can ge aquarium clamps to restrict tubes (the clamps that go onto aerators)
Friend in work was in navy, working on carriers when they still used some piston engined planes, he said they dropped 3"~4" pipe into the ocean and would draw 28 ft of water, blew a few engines if pilot/mechanic  'blipped' throttles too quick
PJ

Hmmm, that's probably why the Sync Pro doesn't work so well. Mine sucked out the fluid on start but I was in the gas a bit while turning it over. Learning is expensive.

Ordered up the Morgan yesterday. $14 cheaper than the Sync Pro (even shipped from UK) and no fluid.