Hey guys,

I'm having some issues with fuel pressure in my Trans Am (1984, 350, Qjet, Holly electric pump, mallory 3-port regulator). I'm measuring only 4psi of pressure coming to the carb and no matter how I adjust my regulator, up or down, it never changes from 4 and it should be around 7psi. I was reading on the mallory web site that if my return line isn't as large or larger than my supply line, that it can cause problems with fuel pressure. The problem is, my fuel lines are factory stock and the supply line is physically larger than the return line. It takes a 3/8" hose vs a 5/16" hose for the return. Just curoius, but while I need emissions to pass my state inspection, what would happen if I get rid of the regulator all together? The pump says it puts out a max of 7psi anyway. Also, which fuel pressure gauge would you guys recommend? I have one of those ones from Autozone that checks vacuum and fuel PSI but I really don't like how it sets up to read the fuel PSI. Any thoughts and imput would be greatly appreciated, thanks!

 

You should use a regulator so change to a regular carb non return type; one line in / one line to carb.
Are you running out of fuel @ 4psi ?

 

I don't think I am running out of fuel, but I'm having issues where the car won't stay running unless I keep my foot on it but as soon as I take my foot off of it, and let it idle down, it dies. Someone suggested that i'm getting enough fuel in the bowls but not enough to keep the car "running"... when I flutter the pedal to keep it running, I get mad "sucking" from the carb before the car dies. I think I may be somewhere in between a fuel and vacuum issue but I can't keep the car running long enough to figure out which. Damnable thing is, was running fine, exited the freeway when it started to stutter then die when it idled down. that was three weeks ago, hasn't been able to stay running since. if I pour gas down the carb (old lawn mower trick), the car will start just fine, but dies as soon as it idles down. When I slam the gas from idle, the car practically stalls and dies. If I am quick, I can flutter the pedal fast enough to keep it running. I've tried the tricks about the A/V tension but it doesn't seem to do anything to help.

 

If it runs but not at idle then I doubt it is a fuel line supply problem.How does it drive on the road?
Maybe your idle circuits are blocked or you have a big vac leak somewhere ? The fact it dies when you nail it sounds like the accel pump is not adding the extra juice needed to cover up the throttles opening.

 

It was running well enough to be dynoed in July. Even then the dyno shop said they had a hard time getting the car to idle properly. I then broke a couple of valve springs a few weeks apart and replaced the set. I got it running though when cold, it wouldn't hold an idle. once it warmed up it would idle ok but was rough. vacuum gauge would read 10-11 at idle and up to 15 at 2500+rpm but it was never a steady needle, always fluctuating 1gh either way.

I should note that reinstalling my original 25 year old carb fixed my idle issues for the last three days that it was running. When coming back from work, the car started to sputter while I came down an off-ramp from the freeway and I li mped to a parking lot. I got it home by towing it but now when I try and start it, I will pump the gas alot and let it crank, crank, crank...sometimes it will turn ove and start, sometimes it will backfire through the carb. if I pour gas down the carb before cranking it will start 90% of the time though unless I keep my foot on it it will die right away. I put the "new" carb back on becuase that was the one that was tuned by the dyno shop and still nothing.

When I had it running and idling, if I gave it gas, it would practically die unless I feathered the throttle alot. Even then, it still didn't want to work. I did the av tensoin adjust per the faq boards here but it doesn't seem to work. For the three days I actually had it running, it would run great at part throttle and when I slammed on it though it would stuttered around 3500 RPM and not want to go any higher.

Maybe I need bigger primaries? Maybe the carb has a vacuum leak in it? I've replaced all the vacuum hoses and fittings and put a new carb gasket on it and tightend it down. I really don't know where to look next. I put a new EGR on it and now I don't knwo where to look, which is why I started looking at fuel delivery issues. I just don't now if it's the carb, or somewhere else on the car. I can't get it running long enough to cap all the ports on the carb to see if my vacuum gets any better (which would basically isolate my problems to the carb).

 

Don't worry about the return line yet. Fuel pressure and flow problems with your electric pump would be more likely at higher engine speeds where demand is greater.

Go ahead and pull your old carb off and spend an afternoon with a re-build kit and a can of carb cleaner on it. When you put it back on don't re-connect any vacuum lines until you've got it running and dwell set.

Be sure to count turns to seat for the idle mixture screws and the lean stop screw (holds the MCS in) before removing them so they can be initially re-set to original positions. A little help:

https://www.thirdgen.org/forums/carb...-ccc-qjet.html

 

Have you checked your timing?

 

I can't keep it running long enough to check it. Even if I get it started, to check the timing at idle could only be done for a moment before the car died.