TheSamba.com :: View topic - Dual carb setups, do you synchronize your carburetors?

Wed Jan 06, 2010 11:42 am

Hello,

For those of you who run a dual-carb setup, do you ever synchronize the vacuum between the carbs with a manometer?

Wed Jan 06, 2010 12:14 pm

Absolutely.

Wed Jan 06, 2010 1:04 pm

It is a must.
Otherwise, at idle, and at speed, it is like having an engine that is not balanced.
One side producing more power than the other.
Balance tube between the 2 sides helps at idle too.

Wed Jan 06, 2010 1:11 pm

I have a V-twin motorcycle that uses two carburetors. I made a home-made manometer for a few dollars using a yardstick, aquarium tubing, some zip ties and a bit of motor oil.

The plastic circle is a caulking tube plunger, it keeps the aquarium line (99c at the 99c only store) from kinking on the bottom.

You get the oil in the line by placing one end into a bottle of oil and sucking on the other end.

Air bubbles will form on a newly assembled manometer, grabbing the unit by the two dangling lines and singing it above your head will force the pressure of the fluid to the other end of the manometer, and for the air bubbles out of the fluid.

Wed Jan 06, 2010 1:24 pm

I have been using one of these for over 45 years. Still have the original box.

http://www2.cip1.com/ProductDetails.asp?ProductCode=ACC-C10-7115

Wed Jan 06, 2010 6:44 pm

I have both a unisync and a snail style. They each have their uses. For my weber 44IDF carbs(sandrail) I go with the snail, very accurate readings, there are adaptor sets available for different applications also. My rail wouldn't pull itself out of its own tracks without synching the carbs!

Wed Jan 06, 2010 7:16 pm

:?: somebody said no :?:

Wed Jan 06, 2010 7:34 pm

i've used the unisync type. never heard of the manometer. how does it work exactly, are they cheap to make. which is better.

Thu Jan 07, 2010 7:30 am

chubby53 wrote: i've used the unisync type. never heard of the manometer. how does it work exactly, are they cheap to make. which is better.
They measure vacuum from the vacuum port rather then total airflow. They're very similar to the carb sync tool for inline 4's on motorcycles (except using oil rather then mercury). When using them it hangs in the virtical position. Each end of the hose is attached to the vacuum port of each carb (this type will only work for single ventruri carbs, dual Kad's for example, but not dual IDF's). You adjust the idle screw on each carb, when the car is idleing, so the oil level is at the same height in each side of the tube.
Be careful though. Make sure the car will at least sound like it idles well before you plug this in or you can suck all the oil into the carb that has more vacuum.

Thu Jan 07, 2010 8:12 am

Never used a uni-sync or a snail..... Always used "lean best idle" adjustment procedure.... Always do plug readings...... Always do engine balance with the "miss" test .....And one car has run 8 years with duals with no problems one for 4 years with no problems....

Your visual and aural senses are really going to be the final judge if carbs are right....

The minute you get everything set by a sync tool and you feel something is not right and you touch a adjustment screw, all the work with a sync tool is out the window....

Dale

Thu Jan 07, 2010 9:14 am

I have dual Kadrons, and I don't use one.

Thu Jan 07, 2010 9:15 am

Dale M. wrote: Never used a uni-sync or a snail..... Always used best lean idle adjustment procedure.... Always do plug readings...... Always do engine balance with the "miss" test .....And one car has run 8 years with duals with no problems one for 4 years with no problems....

Your visual and aural senses are really going to be the final judge if carbs are right....

The minute you get everything set by a sync tool and you feel something is not right and you touch a adjustment screw, all the work with a sync tool is out the window....

Dale

Please explain your method..

Thu Jan 07, 2010 9:34 am

I get a ton more power out of my dual ICT Weber's when they're synced.
Do it.

Thu Jan 07, 2010 10:25 am

tundrawolf wrote: Dale M. wrote: Never used a uni-sync or a snail..... Always used best lean idle adjustment procedure.... Always do plug readings...... Always do engine balance with the "miss" test .....And one car has run 8 years with duals with no problems one for 4 years with no problems....

Your visual and aural senses are really going to be the final judge if carbs are right....

The minute you get everything set by a sync tool and you feel something is not right and you touch a adjustment screw, all the work with a sync tool is out the window....

Dale

Please explain your method..

" Carburetor Setup and Lean Best Idle Procedure" found any site that deals with WEBERS....

http://www.piercemanifolds.com/tech_spec.htm

"Miss" test is pulling spark plug wire out of dist cap one wire at a time and listening degree of miss engine develops on three cylinders... It's really easy to tell which side of engine is rich/lean depending on degree of miss... Then you richen up lean side by idle speed screw, lean rich side with idle speed screw.... Engine response is actually your sync tool.....

Any body that understands concept can usually straighten out bum adjusted carburetors in about 5-10 minutes..... Assuming no "other engine problem exist" and the linkage is adjusted properly...

Gentleman who has been building ACVW's and running Webers for over 30 years taught me procedure...

Dale

Thu Jan 07, 2010 10:43 am

chubby53 wrote: i've used the unisync type. never heard of the manometer. how does it work exactly, are they cheap to make. which is better.

Do GOOGLE search on manometer....... Dozens of concepts.... Best concept would be one tube for each carb throat so you can see responses side by side....

One pretty good description......

http://www.transcat.com/technical-reference/newsletters/Manometer_Merium.htm

IF you are really serious ....

http://www.piercemanifolds.com/accessories.htm

Item #18003

Dale

Thu Jan 07, 2010 10:45 am

Russ Wolfe wrote:
Balance tube between the 2 sides helps at idle too.

On a dual Weber IDF/IDA or HPMX setup ?

Dale

Thu Jan 07, 2010 11:57 am

It sure helps.

Thu Jan 07, 2010 3:31 pm

Balancing at Idle (resting on idle screws) with unloaded linkage is one thing to adjust.
Use your snail or bubbles on this. However:

Your progression of throttle opening thereafter is another thing to watch.

Both carbs need to tighten-up and open at the same time coming off the
idle screws. This is the more difficult thing to get right and maintain.

It may look close but can be dynamically far off in this respect.

The "feel and hearing" theory comes into play here.

As soon as my linkage is off a bit I can feel and hear a lumpy or chuggy
engine sound due to the uneven tip-in of my throttle bodies.
I lose my smooth buttery feel on take-offs.

Now, my idle screw position remains confidently unchanged so I merely
find the side of the linkage that is ahead of the other guy by putting one finger on each throttle while someone gently presses the gas pedal.
Your fingers are better than your eyes here!

Adjust till your fingers can't tell which one is lifting first and your there.

I hear so many beetles take-off and I can just hear the uneven tip-in
of there duals. And that's after the pro's "guage" adjusted it?

I set mine about twice a carshow season and what a difference when it's
dynamically right on!

Thu Jan 07, 2010 3:38 pm

You should also check the balance at about 2500 rpm, after the idle and roll in is right.

Thu Jan 07, 2010 6:55 pm

junior55 wrote: Balancing at Idle (resting on idle screws) with unloaded linkage is one thing to adjust.
Use your snail or bubbles on this. However:

Your progression of throttle opening thereafter is another thing to watch.

Both carbs need to tighten-up and open at the same time coming off the
idle screws. This is the more difficult thing to get right and maintain.

It may look close but can be dynamically far off in this respect.

The "feel and hearing" theory comes into play here.

As soon as my linkage is off a bit I can feel and hear a lumpy or chuggy
engine sound due to the uneven tip-in of my throttle bodies.
I lose my smooth buttery feel on take-offs.

Now, my idle screw position remains confidently unchanged so I merely
find the side of the linkage that is ahead of the other guy by putting one finger on each throttle while someone gently presses the gas pedal.
Your fingers are better than your eyes here!

Adjust till your fingers can't tell which one is lifting first and your there.

I hear so many beetles take-off and I can just hear the uneven tip-in
of there duals. And that's after the pro's "guage" adjusted it?

I set mine about twice a carshow season and what a difference when it's
dynamically right on!

Ditto...

Dale