Setting the Mixture on a Carter YF Carburetor
Compiled by J.P. Hansen from Posts at JeepForum.com
The YF carburetor has a mixture needle that travels up and down inside the main jet. The deeper this needle sits in the main jet the leaner the mixture. The height of the needle during driving is dependent upon the amount of vacuum in the engine and position of the throttle. So the more load on the engine, the richer the mixture. There are conditions, like WOT (wide open throttle) that the needle is pulled further out of the main jet further to force a rich mixture.
A lot of people think that the accelerator pump is just for shooting in a steam of gas during acceleration, but it actually controls the mixture of the carburetor as well. A small amount of vacuum is bled into the bottom side of the accelerator pump and this pulls the mixture needle down. If you had a bad vacuum leak or a plugged vacuum passage then the carb would think there is no vacuum and richen your mixture.
Two things are important:
1. Make sure the accelerator piston is fully pushed down before tightening the housing.
2. When adjusting the needle height, make sure your pushing down on the accelerator assembly again.
Turning the needle height screw one way or the other will richen or lean out the main fuel mixture.
Don’t get gasket sealant down inside the vacuum passages. A very thin coat of HT axle grease is recommended. If the surfaces are flat, that is all you will ever need. Most mating surfaces have a little bead going around the perimeter that helps with sealing the carb. Don’t file off this bead.
Remember having a no vacuum leaks is important for economy otherwise the YF will run rich all the time.
Also, remember there should be two balls or one ball and a loner counter weight. Some kits include what looks to be an extra float valve, but it is also used to replace the ball and counter weight. If using one of these, DO NOT use a ball to re-seat the accelerator check ‘ball’.
See 8 , 46 and 47
From the Jeep forum – I could not even get my YF adjusted with the Prestolight ignition system. When I switched over to an e-core and Duraspark ignition, it was easy to adjust and typically get 18-20 mpg out of the Jeep during the summer.
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These instructions are very vague:
“Also, remember there should be two balls or one ball and a loner counter weight. Some kits include what looks to be an extra float valve, but it is also used to replace the ball and counter weight.”
“Should be two balls” Where? Or is one ball the check ball and the other ball the weight?
When should the aluminum ball in the kit be used?
What is a float valve? Do you mean the extra needle and seat?
How could THAT be used as an accelerator check ball??
Typos in these two sentences sentence::
“When adjusting the needle height, make sure your pushing down on the accelerator assembly again.”
“Remember having a no vacuum leaks is important for economy otherwise the YF will run rich all the time.”
Cheers,
Terry