Fuel pressure reactions

-
85glht

85glht

Well-Known Member
Joined
Apr 25, 2006
Messages
1,612
Reaction score
5,818
Location
CT.
If you ran your fuel pressure at say 6psi, then bumped it up to 7.5psi, would it effect the air fuel ratio? Ie, make the engine run a little richer at different throttle positions.
 
Indirectly, yes it can if running a carb. You may be able to readjust floats, but 7.5 PSI is pushing the limits for a Holley needle and seat.
 
Ok. Thanks for the quick reply. Got it set at 6psi now. Just have to wait for the rain to stop to take it for a ride.
 
If you don't touch the float setting, the fuel level in the bowl will increase as inlet pressure increases. That is because it requires slightly more force is required to close the needle, meaning the float must be further under. The technical terms are "droop" or "bias" of a proportional controller. This might be a simple way to tweak O/F ratio if you have an adjustable regulator. Of course, traditional carburetor adjustment is to set the fuel level at the factory setting and change jets or rod settings.
 
Reason why I asked is that I have a rich condition at cruise that I did not have last fall. I noticed that my fuel pressure was at 7.5 psi. I backed it off to 6 psi. I will take the car for a ride tomorrow..... It is raining here still. I'll post what I find. Thanks!
 
Wideband O2 sensors are dropping in price. I am trying to work them into all my old cars (except my diesels). It is hard to really know what a carb is doing without one.
 
BillGrissom said:
Wideband O2 sensors are dropping in price. I am trying to work them into all my old cars (except my diesels). It is hard to really know what a carb is doing without one.
Click to expand...


I have one in the car. I wouldn't have it any other way. It is such an invaluable tool for tuning.

I finally took the car for a ride the afternoon, all is well. Except for half throttle. It seems a little lean. But WOT looks a little fat. Going to the dyno tomorrow :)
 
If your carb has adjustable air bleeds, you could try a slight smaller IAB, the outer one in the venturi area to see if it fattens up the cruise a little. Go down about .003 at a time and see how it reacts. This will require you resetting the idle mixture screws, most likely a little more in.

Another, raise the float level about 1/16-1/8 turn.

WOT, pull jet out of it.
 
All is good. Straightened it out on the dyno. Wot was a hair fat but safe. Air fuel ratio was 12:2- 12:4. Had a slight stumble and we fixed it with accelerator pump adjustments and stepped up on the squirters. All in all, the car laid down 404hp and 407 torque..... at the wheels. I'm very happy with it. 9.0 pump gas engine to boot:cheers:


Thanks again everyone for chiming in!!!!
 
You must log in or register to reply here.
-

Back
Top