Skip to main content


First of all, I apologize for making another carburetor thread. I know that this subject has already been widely covered on this site. I am looking for advice selecting between two specific carburetors.
I have two Holley Ultra Double Pumpers in the 650cfm and 750cfm flavors. Part numbers 076650bk and 076750bk.

The 650 has 63 main jets and 73 secondary jets.

The 750 has 73 main jets and 80 secondary jets.

The 750 has down leg boosters and the 650 has the standard ones shown in the picture.

I would like to return one of the two and keep the other for use on my car. My car is a replica Lola T70 on a steel tube chassis and weighs around 2300 lbs. It has a Cleveland engine that was built by Hall Pantera in the 1990’s but I do not know the specs. For what it is worth, I have looked into the cylinders with a bore scope and the pistons are flat with valve reliefs cut in the them. The engine seems to be fairly mild, nothing too hot. At some point I would like to upgrade the cam. The engine had a 600cfm vacuum secondary on it that was in need of a rebuild and I thought it would be best to upgrade to something bigger rather than rebuild.

I am leaning towards keeping the 750 but I am unsure if this is correct, as I have read that some here say it will be too rich in a mild engine and that I will loose low end drivability.

I know that with the limited information I have provided it is difficult to determine what is best but I do appreciate any advice.
Thank you


Images (2)
  • 0F0DCE3E-8DF2-47E9-9194-A10221650D6A
  • 79A2AC9E-33D2-4636-A1D9-4DF9D51B6CCA
Original Post

Replies sorted oldest to newest

@rocky posted:

I would keep the 750.

Mine drives great, and really takes off above 3000 RPM. Your Lola looks like it needs something like that.

Thank you Rocky! It’s good to know that the 750 will work and still give me room to grow. I hope it will wake up the Cleveland a bit! I also have an Edelbrock Torker intake that I will try out to see how I like the single plane setup.
The Lola has been fun, I am learning a lot and doing more wrenching/researching than driving lately. It’s the first non production car I have owned and it is making me work to earn it. It was built in the 70’s and enjoyed by its original owner for many years. It sat outside for a few years before I got it so there has been a lot of sorting to do. I am slowly chipping away at things when I have spare time.

@marlinjack posted:

...The 'Torquer' single plane, I use to run, can have a fuel distribution problem, concerning cylinder #8. Also idles more rough.

On the street, Idling at a red light, the driver behind you, will be severely tearing-up.

My opinion...take the jets out of the 600, Install them on the 750 and you'll be Dead-On.


Thank you MJ!
The motor currently has an aluminum dual plane that looks similar to the edelbrock performer but with no logo in the casting. I was hoping to the single plane would yield some more top end. The cylinder 8 fueling problems you experienced sound concerning, is this a common issue with the Torker?
I guess I will be buying a jet kit to avoid committing chemical warfare against drivers behind me

Last edited by Elliott

Add Reply

Link copied to your clipboard.