Carb synch question

Xjers:

Finally built my homemade manometer yesterday. I used Marvel Mystery Oil (which is red) against a white board - very easy to see.

My question - my carbs were perfectly balanced at idle, but as soon as I gave it a little throttle (~2500 - 3000 rpm) the oil in the right tube would start climbing. (Note: my baby Seca is just a twin.)

I then adjusted the balancing screw so the left carb was pulling a slightly stronger vacuum at idle, with the oil in the left tube slowly rising. But again, as soon as some throttle was applied, the right carb showed more vacuum and the oil in the right side started climbing.

Do I just balance them at idle and forget the rest, or is something amiss with the vacuum slides (terminology?)?

Thanks-
Herb

 

I set the balance at idle then blip the throttle to see if it comes back balanced. I do this until I get a repeatable result. It is not uncommon to see one cylinder take off ahead of the others just as long as all cylinders rise as the throttle is blipped. A dominate cylinder is usually the result of a better compression cylinder or a weak valve in the other cylinder.
I would set the sync at idle then check the valve clearances and compression. If those are good then I wouldn't worry. Remember that the manometer is highly sensitive, so much so that the weight of the screwdriver resting on the sync screw can change the reading. So one cylinder jumping ahead of the other may not be too big a deal.

 

Do a "Clunk Test"

Waddia got tuh lose?

 

You went and answered your own question:

The carbs are doing exactly what they're supposed to, and when you give it throttle there's no way your manometer could keep up with it.

When balancing carbs you do it at idle.

You can blip the throttle to see where the levels settle back down to (to make sure they're still even), but anything else is unneeded.

 

The instructions that came with my manometer cautioned against "blipping the throttle" in the event that mercury could be ingested into the engine. All you are trying to accomplish is to balance the airflow (vacuum) across the throttle plates at idle. Blipping the throttle is neither necessary or helpful. I would imagine the same would hold true for oil/liquid filled tubes as well.

 

Many thanks for the tips and clarifications, guys.

Herb

 

I have to disagree. Yes mercury can be ingested this way. No argument there. BUT only if the throttle is blipped too much. What blipping does is to relieve any tension on the sync screws or springs so that a stable result is known. The sync manometer is so sensitive that the weight of the screwdriver can affect the readings. So a quick blip shows you that you really acheived the setting change you wanted rather than just pushing the sync screw down.

 

OK-thanks for clarifying that.

 

Mercury sucked into the intakes will be vaporized in the combustion chamber and IMMEDIATELY released into the environment.

Mercury Vapor is a well documented, known, deadly carcinogen.
Mercury Vapor is a well documented, known, deadly carcinogen.
Mercury Vapor is a well documented, known, deadly carcinogen.

On the other hand ...

Marvel Mystery Oil is a well documented, known, Top Cylinder Lubricant that has miraculous engine healing properties.

Old School Tuners, working on Side Draft Carbs, would often shoot some Marvel Mystery Oil ... right straight into the carbs intake side with the engine bumped-up to fast idle.

Marvel Mystery Oil is one of my very favorite aroma's ... right after Christmas Tree, Old Spice After-shave and one other thing.

 

Mmmmm... yummy. It even smells good when passing through the combustion chamber at 4K RPM.