Big and small venturi Crate carbs

[rangerover]

My buddy bought a nice used northern sportmod with a 602 crate. It came with 2 crate carburetors, but we noticed that the Karl carb has small venturis. The Willys carb has venturi about 1/8" larger. Is one a 650 and the other a 750? They're both supposed to be for 602 crate. Which should we run?

[save the racers]

I would start with the smaller carb.I've see smaller carbs make more power on the lower hp motors.It is common for us to carry 2 carbs and switch to the bigger carb if the track slicks off.

[brad hibbard]

1.250" venturi size is a 650 and 1.375" venturi size is a 750

you will see more throttle response and low end power with the smaller venturi

i agree with the last post--when the track goes to a slick condition the 750 will be more driver friendly

Brad

https://www.race-1.com

[50j]

It could be a goofy 390 and a 650. Best to measure.

[rangerover]

Thanks for the responses. I found out 1 is 1.250 and the other is about 1.380 as was stated above. We're leaving the smaller Karl carb. It came with 72 jets and the previous owner ran straight Sunoco 110 race gas. We're thinking of mixing 110 with 91 pump gas 50/50. Think this will be ok on this 602 crate? Should we leave the 72 Jets and timing at 34?

[powerslide]

Its a 9-1 motor. It will probably run on 87. But at min I would put Premium in it. They suggest 91. That's part of the money savings on a crate you don't have to run $7 a gallon fuel in it.

[rangerover]

Makes sense. Thanks guys.