Fishhawk

After finishing my engine and drivetrain mods on my 85 GT I felt I needed a little help with fuel delivery. I installed a Carter mechanical fuel pump and larger pump to carb fuel line. The car ran great when I tested it, however I didn't really run it through the gears at WOT. So on Sunday its off to the track to make some 1/4 mile passes. First and Second gear were no problem. Flirted with the rev limiter in both gears, hit third and climbed to about 4500 RPM when the motor started to bog, acting like it was hitting the rev limiter. Shifted into forth and it continued to run like s---. At the end of the 1/4 mile when the motor had come to an idle it was running fine. It also was running fine on the drive back to my pit. Shut in off and everything checked out okay. Decided to make another pass and had the same results. Drove it home at highway speeds (75 MPH) with no problems. Just didn't hit any high RPM's. Did my new high volume fuel pump stink the stock line dry? Is my stock fuel sending unit and stock tank to pump fuel line to small? If so does anyone know of a company that sells a higher volume sending unit (say 1/2 inch outlet). I will of course need to install 1/2 inch line. I really would appreciate your thoughts and opinions. Thanks in advance.

Mberglo

Hmmm. So first and second gear were fine, even though you were wrapping it up past 5000? The engine uses just as much fuel in first gear at 5000rpm as it does in third gear at 5000rpm.

I don't really have any suggestions though. Sorry.

Fishhawk

One way or another the carb isn't getting enough gas. Its either the bowls are going dry because the carb isn't big enough or the line is being stinked dry from the pump because it isn't big enough. I'd hate to by a bigger carb only to find out all I needed was a bigger line, or buy line then still have to put on a bigger carb.

Coupe

Perhaps you created a vacumn leak from the chassis vibrations, one that only shows up when your blasting down the track

You could put in a cheapo clear Fram gas line filter. If it is dry at the end of a run, you have your answer.

Or: go larger fuel line from pump to tank.

Or: replace the line and the carb with an Edelbrock...

Mberglo

But if other Foxes are running down the track with stock pumps and lines, I don't know why yours would be running dry. Unless your float level needs to be adjusted higher.

Fishhawk

All the other Fox bodies are fuel injected. But I was also thinking that the carb needed a float adjustment.
The line from carb to fuel pump is 3/8 inch. That should be fine. The line from tank to pump is the stock 5/16th. Also the Holley was just rebuilt and a metering block was added. I'm hoping all I have is an adjustment problem. But lately I've been following Murphys law, so I expect the worst. (Drilling a hole in the bottom of my tank and adding
a drop sump, adding 1/2 inch line to the pump, and a 650 CFM carb.)

Mberglo

As you well know, the Foxes from 79 to 85 were carbed. Nonetheless, I think the size of your fuel line is probably not the problem. I'd suspect a carb setting. Can you borrow a different carb and try a pass or two?

Fishhawk

Right. What I meant was, all the fox cars running this weekend were fuel injected. Also you must be reading my mind. I was talking to a engine guy who says he has a 750 holley he wants to throw on to see if its the carb or the line. I'm thinking a fuel preasure gauge t'd into the line between the fuel pump and carb would tell me if its the line or the carb.

conv_stang

you could also get out on a stretch of highway and run through the gears and see if the same happens. sounds like the pump is coming unsubmerged under hard acceleration. causing all the fuel to the back of the tank. sort of similar to oil starvation of an engine from high cornering loads

Fishhawk

It did the same on the highway. Of course I was high in the R's then to. However, I had 3/4 of a tank of gas. Someone just suggested to me it might be timing advance. Thats funny because my first thought when it happened was an ignition problem.

conv_stang

well im all out of ideas good luck. hopefully wont be too much trouble

Fishhawk

Talked to a few more people and I'm pretty much cionvinced the stock 5/16th fuel line is to small.

Daysleepin

I gots to weigh in on this one

Though its just a guess that comes from my own personal experiance.

My 65 two barrel seemed to run fine until I kicked REAL HARD.

I took a screw driver and put it down into the carburater in a way that would hold open the metal flap (AKA Choke).
This resulted in scratch in all 4 gears.

You might try to wire the choke open with a twisty ty from a bread wrapper.
Won't cost you anything but your time to test it

Any way. it is just a guess that the higher RPMs are also higher vacuum and maybe causing the choke to close at when it should not?

Let me know? Good luck.

Fishhawk

I know its been a long time but the remedy to the problem was all the old rubber fuel line. The new high volume pump was stinking the old hoses shut and they wouldn't open until I had slowed down. I replaced the line with 1/2" aluminum line and all the hoses and now the carb's getting all the gas it needs.

Coupe

Thanks for posting the solution to your problem. Perhaps when someone else has the same problem, they will be able to find a solution in this follow-up post.