Cliff's Quadrajet Parts and Rebuild Kits

General Category => Quadrajet Carb Talk and Tips => Topic started by: Mr.Pontiac on September 20, 2018, 09:16:47 PM

Title: Do i need a bigger needle and seat???
Post by: Mr.Pontiac on September 20, 2018, 09:16:47 PM

My bracket car was a consistant 12.20,s 107 mph car, decided to switch to a bigger hydraulic crower cam, Car now picked up et to 11.90,s but mph dropped to 102-3. do i need a bigger needle and seat, running a .135 now????

Title: Re: Do i need a bigger needle and seat???
Post by: Cliff Ruggles on September 21, 2018, 03:52:04 AM

What is the fuel delivery system?  What fuel pressure?

Title: Re: Do i need a bigger needle and seat???
Post by: Mr.Pontiac on September 21, 2018, 05:30:37 AM

Sumped tank, no.8 to electric pump and filter then no.8 to regulator and no.6 to carb.. Car has always ran 6.5 psi.

Title: Re: Do i need a bigger needle and seat???
Post by: Mr.Pontiac on September 21, 2018, 05:38:43 PM

New cam 296 HDP IF IT HELPS

Title: Re: Do i need a bigger needle and seat???
Post by: Cliff Ruggles on September 22, 2018, 12:52:48 AM

Difficult to say as you didn't put up the pump specs, type of electric pump or location.

Assuming it's at least 110GPH and located behind the tank the .135" seat should be adequate for the power level.

Never hurts to try a larger .140" or .145" seat to see if anything improves. 

My car is fine with either, didn't see any improvement going from a .135" to .145", but I left the .145" in place just to give me a "warm and fuzzy".

My system is also a sumped factory tank, 8an lines to a high flow filter, 140GPH electric pump behind the tank, and 8AN lines/fittings all the way to the nose of the carburetor.  Just ahead of the carb I have a pressure regulator set at 7.5 psi and return system back to the tank to take the load off the pump for "normal" driving......Cliff

Title: Re: Do i need a bigger needle and seat???
Post by: Mr.Pontiac on September 22, 2018, 04:43:52 AM

Cliff, sorry , yes 110gpm behind the tank. I also have a return back to tank with a no. 10 hose. alot of cam, just trying to figure out why i lost the 3 mph. You stated you run 7.5 psi i am at 6.5 maybe a need for more fuel??? reason i asked

Title: Re: Do i need a bigger needle and seat???
Post by: Sonny on September 22, 2018, 06:50:00 AM

A decrease in pressure should increase volume.

Title: Re: Do i need a bigger needle and seat???
Post by: Cliff Ruggles on September 23, 2018, 03:59:29 AM

The later carburetors will easily handle high fuel pressure so don't be afraid to crank up the pressure some and see if MPH improves.

You'd think a bigger cam would make more top end power and MPH would go up some, especially if ET improved......Cliff

Title: Re: Do i need a bigger needle and seat???
Post by: 77cruiser on September 23, 2018, 04:37:52 AM

Did the 1/8 mph drop off too?

Title: Re: Do i need a bigger needle and seat???
Post by: Mr.Pontiac on September 23, 2018, 04:45:53 PM

I believe  i found the issue, no.1 and 7 plug completely fouled. Hay i ran these plugs for just about a yr. guess i should not complain

Title: Re: Do i need a bigger needle and seat???
Post by: 77cruiser on September 23, 2018, 07:43:58 PM

Gonna be fast on 8 then. Let us know what it runs when tuned up.