Topic: Carburetor Idle Mixture Screws - No Effect?


carcrazy    -- 04-21-2014 @ 11:13 AM
  The carburetor idle mixture screws have no effect on the idle quality when turned all the way in. What is happening?


cliftford    -- 04-21-2014 @ 12:39 PM
  My guess is the power valve, gasket, or the vacuum passage that controls it is at fault.


ken ct.    -- 04-21-2014 @ 4:00 PM
  Engine is getting gas to run from a leaky power valve or a bad gasket there.Replace PV with a 5.5 and a proper gasket. ken ct. You will also need a base to middle section gasket.


supereal    -- 04-21-2014 @ 5:48 PM
  Pull the needles and inspect the tip to see if they were over tightened. If you see a ring, chances are the seats have been enlarged to the point the needles don't seat. Also look for a vacuum leak around the carb or intake manifold. A cracked or loose wiper hose will affect the idle circuit.


Old Henry    -- 04-21-2014 @ 7:10 PM
  Also, make sure that the throttle plates are closing all the way. Screw the idle speed screw out far enough to make sure. Any air or gas leak anywhere will defeat the idle screws.


carcrazy    -- 04-22-2014 @ 5:18 PM
  Thank you gentlemen. Thanks to your excellent advice this problem has been solved and the idle mixture screws now have full range of authority. The power valve was the culprit - the sealing surface had a radius that prevented it from making a tight seal even with two gaskets.


TomO    -- 04-23-2014 @ 7:25 AM
  As a rule of thumb, if 1 gasket does not seal, 2 gaskets will increase the chance of a leak by 100%.

Tom


supereal    -- 04-23-2014 @ 2:42 PM
  At our shop, we have been turning the gasket surface on power valves to eliminate the radius. This seems to cure the leakage, particularly with the triangle gaskets.


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