Carb Fuel Level

Mulletwagon

Mulletwagon

Well-known member
Checked the fuel level using a clear flexible tube and determined the level is 3/4 inch below the parting line rather than the traditional 5/8 inch on my Zenith carb. Suspect this is resulting in a leaner mixture but just wondering how much. Not getting any pinging but have a little bit of a rough idle which may not be related. If I shim the inlet valve with a thinner seal to get the 5/8 inch level am I likely to notice any performance difference ? Know the spec is within 1/64th of 5/8 inch just don't know if 1/8 inch low is significant enough to make a difference. Watcha think ?
 
A gas level in the bowl 3/4 in. below the machined surface of the lower casting should be just fine. It is better than the 5/8 in. level because if at 5/8 in. the gas level is high enough to put gas right at the top of the Main Jet and the Cap Jet. The carb may not leak but it could smell. "The running nose affect." If you parked your car going up a steep hill, gas most likely will be leaking out of the carb intake. This lower level will not affect performance because the Compensator Jet is still well submerged in gas in the bowl. Ed
 
Mulletwagon said:
Checked the fuel level using a clear flexible tube and determined the level is 3/4 inch below the parting line rather than the traditional 5/8 inch on my Zenith carb. Suspect this is resulting in a leaner mixture but just wondering how much. Not getting any pinging but have a little bit of a rough idle which may not be related. If I shim the inlet valve with a thinner seal to get the 5/8 inch level am I likely to notice any performance difference ? Know the spec is within 1/64th of 5/8 inch just don't know if 1/8 inch low is significant enough to make a difference. Watcha think ?
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It has been my experience that a fuel level 3/4" below the seam will run just fine. People anguish over this measurement too much. However, I would not go much less than the 5/8" because then you really are too high and the carb will weep.

The rough idle is unrelated.
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I bought a new float valve and a tube I can use to measure the fuel level. My car seems to run lean at idle, yet often smells like gas. I hope the idle smooths out and the gas smell goes away after I put in the new valve and adjust the level.
 
bdtutton said:
I bought a new float valve and a tube I can use to measure the fuel level. My car seems to run lean at idle, yet often smells like gas. I hope the idle smooths out and the gas smell goes away after I put in the new valve and adjust the level.
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Do you notice the gas smell while the motor is running, or after a while when you turn off the motor and gas valve?


When idling is there black smoke coming out the Tail pipe? - this would indicate you may need to adjust the carb idle screw/mixture.




If smelling it after turning the motor off, after a hour or so it is possible you have a leaking Gas Shut off, in addition to a float valve/seat that does not seat properly.
 
I believe the rough idle is unrelated to the gasoline smells. As others have said, your float valve may be leaking and then gas will spill out the Main and Cap Jets. Your rough idle could be from a clogged or an Idle Jet that is not sized properly. The Idle Jet should be flow tested per Steve Pargater's manual. The Idle Jet is the most difficult jet to get sized properly because its flow is low (44-48 ml/min.) and the range is very narrow. If the jet has to be soldered up, and re-sized, you have to be very patient to get to a correct flow rate. Ed
 
Jim/TX/GA said:
It has been my experience that a fuel level 3/4" below the seam will run just fine. People anguish over this measurement too much. However, I would not go much less than the 5/8" because then you really are too high and the carb will weep.

The rough idle is unrelated.
.
Click to expand...



Have also heard 15/16 used - Comments about this?
 
Been researching and have seen suggestions that anywhere from 9/16 to 3/4 is considered acceptable. In my case I cleaned the carb and discovered the inlet valve was shimmed with two .050 seals which resulted in the 3/4 fuel level. I removed one of the seals and the resulting fuel level was 5/8. Did not notice any real difference in performance.
 
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