Thanks for the replies and ideas. Hopefully I'll have a chance to try some before we get snow and salt on the roads.  Thanks again.  Dave V

SE Wis

While I was playing with the accelerator pump on my 570, I noticed that some of the cams would not operate the pump arm immediately, I think in position 1.  That can cause hesitation.  Make sure the accelerator pump is operating correctly.



Lawrenceville, GA

Hesitation issues are typically a result of a lean condition which can be fixed from several different approaches.  Gary is correct in that richening up the primary jetting can help with hesitation issues.  A larger accelerator pump shooter and/or pump cam can also help.  Reducing the idle feed air restriction holes is another option.  Balancing the primary and secondary throttle blades so that the transition slot in the primary side is not overly exposed is also another fix.  I’ve gone so far as to change out the fuel discharge nozzles to a different design on some carbs in which to increase the booster signal at low rpms.

Lorena, Texas (South of Waco)

Thanks for the reply Gary.  Now I'm confused. Doesn't coming off idle have more to do with the accelerator pump and discharge nozzles?  Dave V

SE Wis

Try jetting up two sizes on the primaries only, that works more often than not.

-Gary Burnette-

Ted.  I've been having trouble eliminating a hesitation off idle with a 600 Holley on my 312. Put a 390 Holley on it and it runs good now but without the performance that I would like. I was going to buy a 500 Edelbrock for something in between but from what i read the Summit 750 should work for me?  Dave V

SE Wis

Harry.  Based on the results you were having at Columbus, I tested that same 750 cfm carb on a 303” Y with unported '113' heads and iron intake and was very pleased with the dyno results.  315HP and a very broad torque band.  That engine is back in a ’56 Ford Victoria with highway gears and runs very well at all rpms with great driveability in stop and go traffic.  The fuel mileage is also good even with ethanol laden fuels.  It gets my vote also.

What helps to make that larger carb work well are the annular discharge boosters which allows for a reinforced vacuum signal thus compensating for the larger throttle bores.  This carb ends up with good low rpm response and the cfm to accommodate some good rpms even on a smaller cubed engine.  I’ve also run the smaller 600 cfm versions on engines but have no comparisons to its larger version on the same engine.

Lorena, Texas (South of Waco)

Summit carb results
For my 2 cents worth on the Summit carb.I am using the 750 Vac secondary model on my 60 Merc which is 3800 lbs. + of car and driver  which is going 12.60's at 110 MPH  with the help of Mummert Heads and intake ported by Joe Craine.The car went 12.70 with the carb out of the box after I got traction and then broken axle problems taken care of. I am sure there made by Holley as it uses all Holley parts, jets, vac parts, power valves ect. The carb sold by Summit is a copy of the one Holley made years ago models 4010 & 4011 which was a copy of the AutoLlite carb but with some improvements.So the Summit carb gets my vote. They also offer that in 650 CFM also.  Harry Hutten

Carburetor choice for a Y-block, or any other engine will depend on a number of things. What will you be using the car for and what do you want as far as driving experience? Is it a cruiser or is it a drag strip car? What transmission and rear axle? How heavy and what cam and or other modification have been done? To try to answer what carburetor is "best' is a question without a rational answer. Pete 

Darell, 
           Sorry, don't get here everyday. Yes to the pressure gage. All Lokar says that I remember is to make sure the lever on the tranny moves as soon as the throttle begins to open. They supply you with very good instructions. If you don't have them I'd recommend going to their website and finding out which hole to use. Remember there were multiple versions of this tranny from trucks to Lincoln Mark VII's and Mustang GT's all of which used different levers and settings. Without knowing what your was I can't tell you much more. 

Frank/Rebop

Bristol, In ( by Elkhart)