#1. My car has a stumble at rpms in between 1700 and 2000. the exact position where the stumble happens varies, and it seems to be worse the less load is on the engine, like when i am going downhill. the engine feels like it misses as i give it gas from idle speeds. if i am coasting downhill at 1000rpm or so and decide to press the pedal down, the car stumbles and jerks pretty bad betwee 1700 and 2000 rpm. Don't know if it is a carb tuning issue or a timing thing. Oh yeah. 625cfm carter afb on a 350. 5 speed trans. no computer/emissions and stuff.

#2 what kind of fuel pressure readings should a manual fuel pump produce. seems to be really erratic.

sorry for the length, hope somebody can help.
thanks

 

#2) Between 1 1/2# to 3#.

-Auggie-

 

That low? Mine reads about 5lbs at idle and around 7lbs at 2000rpm. Maybe I did something wrong or can't quite remember. The needle does jump around a lot, so these are just averages

 

Mike, you must be checking the fuel pump pressure by removing the fuel line at the carb and installing a fuel pressure gauge on the end of the fuel line and checking pressure at eng. idle. That is the way that most SM tell you to check fuel pressure and if that is the way you are doing it your readings seem ok. The spec in my book is 5 1/2# to 6 1/2#. When i installed my NOS system they said that i must have between 4 1/2# to 5 1/2# of fuel pump pressure. So i checked my pump pressure useing this method and had 5 1/2#. I thought i was ok and went out and blew the head gaskets and melted a bunch of plugs. If it wasn't for the knock sensor i would have blowen the eng. What they left out of their instructions is that i needed between 4 1/2# to 5 1/2# of fuel pump pressure at "WOT". I went out and bought a Stewart Warner elect. fuel pressure gauge. I made up a "T" and installed it in the fuel line right next to the carb fuel inlet. I screwed the gauge sending unit into the "T" and wired it up. I went for a test ride and at 6000 rpm i had 1 1/2# of fuel pump pressure far from what was required. So i installed an elect. fuel pump to help the mech. pump at WOT and have had no problems since. SO! the figures i gave you were for checking fuel pressure with a "T" in the fuel line. You can also do a fuel pump flow test. Disconnect the fuel line at the carb and useing a piece of rubber fuel line hold it into a container (1 qt) and run the eng. at idle. You should pump (1) pint of fuel in 30 sec. That is the minimum spec. If you have any more questions let me know.

-Auggie-

 

Auggie,
Here is what I did. I just have a Mr. Gasket mechanical fuel press. gauge from the local "speed shop". It came with a brass fitting that had nipples for the fuel line on each end and a threaded hole in the middle. This hole is where the actual gauge screws in. So in effect the gauge is tee'd into the fuel line. Or am I misunderstanding? Hopefully I'll understand this time around. Thanks.

 

Mike if you have between 5 and 7# of fuel pressure at those rpm and checking with a "T" in the fuel line that would seem a little high. What kind of pump do you have?
If its a mech pump does it have a return line back to the tank?
-Auggie-

[This message has been edited by Auggie (edited November 16, 2000).]

 

Yeah it is a mechanical pump (i think a stock melling unit) with no return to the tank. How would I go about plumbing one of those? Oh yeah, I did some reading on the edelbrock page and it mentioned that high fuel pressure at idle could cause stalls with hard braking/turning. I have noticed that the engine tries to die when i brake or turn hard, so I think that I should try to reduce the pressure a bit. Thanks again

 

What year is your car? Is the plumbing for the fuel pump return line still intact?

-Auggie-

[This message has been edited by Auggie (edited November 17, 2000).]

 

My car is an '84, but the engine is not factory. Had the V6, but put in a mid seventies rebuilt 350 last year. I can't remember what year I made up to ask for a fuel pump at the autozone, and would have to find the papers to figure what brand it is. I still have the hard line running from the engine bay to the tank for the return, but it is just capped off right now.

 

just ask for an 85 Z28 w/ 305 LG4 and they will give you the pump w/ return fitting

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350, Comp 262, Edelbrock Performer intake 600 cfm carb and exhaust, headers