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One of the butterflies is open about 1/8" with the carburetor dis assembled.

1st check to make sure the fast idle linkage isn't holding the valves open. Probably not since only one butterfly is open. Both valves should be closed. Someone has installed it improperly. When removing valves they should be marked so that they get put back the same way. When replacing them hold them tight against the wall while tightening the screw. When done you should see very little daylight around the valve.


If the secondary throttle plate is staying open, then check the primary shaft dog and spring.

What goes under the power piston.

Power Piston Spring
A spring is inserted in the power piston hole, then the piston.

Fuel is puffing out nozzles on primary circuit at idle on primary carb of a dual carb set carbs were just rebuilt what is the cause. I have taken this carb a part and rechecked floats adjustments and blown out passages with compressed air thank you

WCFB Low Speed JetBlowing out passages will not get them clean enough. Ethanol leaves deposits behind that acts like corrosion. You need to run wire down all small passages. Check the low speed jets to make sure they are clear (#44). Check any vents to make sure they are open.

Make sure there is a check needle below the main discharge. Test the needle by holding it down gently with a brass drift punch. Put some fluid in the accelerator pump well and press down on the pump. You should feel some pressure and fluid should not be bypassing the check needle. If it is, tap gently with a hammer and the same brass drift punch to seat it, or replace the check weight.

Each float on the float assembly should be at the same height and centered so that they don't rub the side of the float bowl. Test the floats in hot water and if you get any bubbles then they are leaking.

Test the fuel pump to be sure it isn't putting out too much pressure. You will need to check your motors manual for the spec, but around 4 or 5 should be plenty. New fuel pumps are especially suspect.

Gas is coming out of the to vent

You are flooding (getting too much gas in the float bowl), caused by these types of problems.

Float adjusted wrong - check float level.
Float leaking - heat up some water and immerse the float. Any bubbles indicates a leak.
Make sure the 2 floats are the same height. Also make sure one isn't rubbing on the side. They need to be centered in the bowl.
Fuel could be leaking around the needle & seat. Did the old gasket get removed? Look for breaks in the new gasket, or cracks around the threaded area.
The needle could have been damaged while adjusting the floats. Any pressure put on the needle will damage it. Examine the viton tip for any marks.
Fuel pump pressure could be too high. Check your auto manual for the spec, but somewhere around 4-5 lbs would be good.
Be sure the power piston is not frozen in one position. It needs to go up and down easily.
Is there a spring under the power piston?
Are the venturi cluster gaskets sitting flat and not curled over? They sometimes need trimming.

When I slow down to an idle, my engine runs rough.

Two ports act as calibrated air bleeds. One is in the secondary venturi and the other just above the throttle plate. Be sure these ports are clear.


When the engine gets hot and then is shut off, gas can sometimes overheat and then boil. This is percolation.

The high speed air bleed and the secondary bleed tube also acts as an anti-percolator. Make sure these are clear if you have percolation problems.

Also check for overheating of the engine, fuel lines too close to the manifold, or too much heat in the engine department.

Try other brands of gas.

Squirters are not working. They work fine when I push hard down on the piston. Piston force is too much for linkage.

There may be a blockage in the accelerator pump circuit which would also make it hard to pump.
What is the carburetor number so we can make sure you have the correct pump?
Polish the pump well with crocus cloth. Ethanol gas does not have much if any lubrication. Run a blunt object around the inside of the leather cup to make sure any coating is broken. Some have a coating to give it a better shelf life.
Add a couple drops of oil to the leather. Is there a pointed check weight in the main discharge hole.

Dies when choke opens.
Engine won't idle, or dies after the choke is opened, or runs better when choke closed.

First thought: curb idle speed is set too low.

Second thought: gasket between bowl and base is installed backwards (easy to do).

Third thought: vacuum leak downstream of carb.

Last thought: secondaries are somehow stuck open (which amounts to a vacuum leak).

More thoughts.
  • Not enough fuel in the float bowl
    • Sticky float valve
    • Low fuel pump pressure - always check you motors manual for the correct pressure. Probably around 4- 4.5lbs
    • Clogged idle tube, or passages in the idle circuit.
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