Adjusting and cleaning Dual Carburetors and air filters

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Adjusting and cleaning Dual Carburetors and air filters

Postby Larry Jowdy » Sun Oct 08, 2006 8:53 am

Tools needed: Carburetor air flow meter (2 kinds are available, one is called a snail and the other has a vertical vacuum port) a screwdriver, a small adjustable wrench, Twist tie from your kitchen. cement mixer (OK, you really don't need a mixer)

First thing is clean the idle jets. Remove the idle jets and make sure you don't lose the small rubber \"o\" ring. Use the twist tie by stripping off the paper. Insert the wire into the small end of the idle jet and make sure they are totally clean.

CLICK ON THE LINK FOR A DIAGRAM OF A WEBER 44, IT SHOWS WHERE THE IDLE JETS ARE LOCATED viewtopic.php?f=19&t=8411

Remove the air cleaners and warm up your engine. While the engine is warming up, take this opportunity to clean your air filters. I use Formula 409 but other liquids are available such as K&N filter cleaner. Spray the outer sides of the filter and use an old tooth brush to remove the dirt. Rinse the filters from the inside out then make like a wind mill and swing the filters until all of the residual water is removed. Let them thoroughly dry and using K&N spray oil, lightly oil the pleats. The oil will wick through out the element so don't over oil them.


Make sure the idle is stable and the oil temp. is up to operating range. I know you've heard this before but make sure you're in a well ventilated area. If not, you won't make it past the warm up procedures.

Remove one of the throttle linkage heim joints and with the engine idling, place either of the volume measuring devices on one of the velocity stacks of a carburetor, it make no difference which one you use.
Note how much air is being drawn into the carburetor.

Next, place the air flow meter on one velocity stack of the other carburetor. Note how much air it is drawing.

If the 2 measurements are different, adjust the idle stop screw on one carburetor to make that air flow reading match the other carburetor. Look at your tachometer, are you somewhere around 900 to 1,100 RPM's?
If so, then you're in the proper range. If the tachometer reading is low, turn up the idle screws (located where the linkage attaches to the carburetor) equally then re-check the air intake volume as described above. Once both carburetors are drawing equal air you've completed the carburetor balancing portion of the adjustment.

The next procedure is to set the air mixture screws. These screws are located at the base of each carburetor barrel and they have a small spring around the screw. It makes no difference which screw you start with so the next step is to gently turn the screw \"\"IN\"\" until the engine starts to pop and the idle drops off. Gently, and I repeat GENTLY, bottom the screw then turn it out (counting the revolutions of the screw) until the highest idle is achieved. If you go too far, the idle will drop off. This MUST be done very slowly to allow the carburetor to catch up with your turning of the air mixture screw. Note how many turns \"out\" it took to achieve the highest idle.
Repeat this step on the air mixture screw next to your starting point. Once this has been accomplished, repeat these steps on the other carburetor. All air mixture screws should be turned out roughly the same number to turns.

Look at you tachometer, if the idle is too high or too low, re-adjust the idle set screws as described above. Re-check the air volume with your air flow gauge and you're just about done.

Turn off the engine and adjust the linkage arms to each carburetor. This is done by loosening the heim joint jamb nuts and rotating the linkage arm. Make sure the idle set screw stop has not moved
In other words, you want to ensure that when you step on the throttle, both carburetors open at the same time.

After you've completed the linkage adjustment, start the engine and check your work.
Last edited by Larry Jowdy on Wed Apr 07, 2010 11:36 am, edited 3 times in total.
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Postby Larry Jowdy » Sat Oct 21, 2006 7:22 am

POSTED BY DANNY P

After you've followed Larry's procedures, rev the engine to 3000 and hold it there. Check at least one barrel on the two separate carbs with your synchrometer, to check high rpm synch. This made a world of difference on my engine with smoothness and low-end pulling power. Also, sight down your heim-linkage, you know the two links from the hex bar to the carb. Do this from the side of the car, at least 10 feet away. If the links are not at exactly the same angle, throttle travel will differ between the carbs. I had to space one of my ball-links on one side to even it out.
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