Idle Jet Too Big??

Pilotdave

Pilotdave

Well-known member
My A wants to run with the mixture adjusted fully lean. Is it likely that the idle jet is too large? Some other cause? No air cleaner on the engine. At least 500 miles on the engine since it was rebuilt. Should I leave this alone or go looking for something to fix??? Thanks much.
 
Ron, I'm referring to the mixture adjusting rod inside the car when I say that the mixture is adjusted fully lean. I've also played a bit with the idle mixture screw on the carb and NOW am realizing that there must be interplay between the two. My library is yet incomplete - am anticipating that it will be much more complete by end of December! But there must be a standard protocol for adjusting the idle mixture and then the mixture rod - can you point me at same? Or tell me that I am off base here? Thanks...
 
I don't know what carburetor you have ? the earlier carbs have a brass removable seat and the later carbs have a cast seat; some of the replacement needles are junk and do not reach the seat so you have no control with your choke rod in the car; you can also have the same type problem with the idle air screw. Both of these problems should have been checked during the rebuild of the carburetor; this would also include the sizing of all the jets including the idle jet. Maybe someone in your local club, who is knowledgeable about carbs could assist you with checking your carb.

Ron
 
Thanks, Ron. Carburetor is a Zenith 1. The choke rod clearly does affect results - opening it even part of a turn results in a too-rich mixture. Another local A'er and I had the carb apart but only replaced the float valve. My worry is that the needle will be deformed as I have the mixture rod fully lean - usually not open even the recommended 1/4 turn.
 
The 1/4 turn is a recommendation, lots of factors go into the actual amount needed. If the car runs fine with it closed, I wouldn't worry about it. Check the spark plugs to get a reading on the mixture.
 
When the car is idling, the Gas Adjusting Valve (GAV or choke rod as you call it) should not affect the idle speed or the optimum idle mixture adjust screw setting. Offhand I don't know what is wrong that the GAV has an affect on the idle mix adjusting screw. I would guess a partially plugged idle jet.
 
I'll have to pull the carburetor off and do some checking. Will also check the plugs and report back in a few days when I can get back to the A project - thanks.
 
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