Fuel pump mod.....

[Freddie's Buick]

Originally posted by b4black
Roe's book says something like 4 psi at WOT, and some Buick manual were saying 5. Then others said a Quadrajet is fine with as little as 2 psi. (I had about 3 pis at WOT.)

Then I found a site that says it's not pressure, but flow that's important. That the carb's fuel bowl can't hold enough for a ¼ mile run. Whith good flow, 2 psi is enough.

In case my pump was bad, I swapped it with a new one I already had (brand unknow). The WOT stumbling improve a little, but was still there.

Then I removed the internal filter in the carb inlet and replaced it with a much larger external filter. (less restriction = more flow) NO STUMBLE!!! 3 psi before the filter dosn't mean much. It's the pressure/flow after the filter that's important.

Originally posted by Freddie's Buick


And finally, remove the OEM internal paper filter. According to Roe a good in-line filter prior to the carb will handle the internal paper element's job just as well. (In-line has less restriction then internal and the flow will increase Just like you wrote about Rich).

Well I installed a Carter fuel pump, Summit in-line fuel gauge and a Russell Clear Flow Plus in-line fuel filter. The flow rate for this filter is about 30-GPH@3.50 PSI according to spec sheet, (total 60GPH@7PSI). The readings I got on my gauge were between 4.50-5.00 PSI. I also took the liberty to remove the carb's internal paper filter.

Removing this filter was a bad idea for me. The pressure was a steady 4.50-5.00 PSI@idle before the carb inlet. The pressure increased to 7-PSI when the engine was shut off. This caused overflow at initial start-up and flooded the carb several times.

The long OEM fuel filter has a check valve inside it. This regulates pressure and prevents overflow. It's like a safety valve. If one has a real good flowing inline filter like the one I got, keep the OEM internal paper filter in the carb. Removing it may cause these types of problems.