killervette666

Hi all,

I have a 79 that I've done a bunch of modifications to. It's got the original L-48 but I put in a more aggressive cam, 650 cfm Speed Demon carb, and a Performer RPM intake.

I had been dealing with a knocking noise and low fuel pressure for as long as I can remember so about 3 weeks ago I went out and bought a new carter fuel pump (with a return line and everything). Everything seemed good until my starter recently crapped out as well (well sort of, I was too stupid to check the ground connection and by the time I did the new starter was in anyways).

Now before these two modifications she ran just fine with no problems. A little hard to start/needed some warming up, but never stalled out on me.

Now here's what happened last weekend. I drove it about 10 miles into the city. Drove fine. Parked, got back in, got half way home and it started dying on me. Basically, when I would be at a stop light, foot on the brake, the engine would appear to surge, the rpms would drop and then come back, and feel like the next time they were going to drop the engine would die. So I just gently eased it into neutral and kept the RPMs high at stop lights. That worked for a bit, about a mile later, I go to press on the gas, and it just flat out dies.

It would start, idle just fine, but when I would put it into drive it would die. In fact, about an hour later when the tow truck showed up, it wouldn't even start up and idle. So I just got it towed home.

Spent all day today redoing the timing (set it to about 18-20 btdc as per carb instructions) reset fuel float levels (they were a lot higher after the new fuel pump) and reset idle screws. It seems to be better, but the engine is still surging up and down when its in drive and foot is on the break. The really weird part is that the longer I drive it/keep my foot on the break, the worse the "sruging" becomes.

What is going on!! I'm out of ideas at this point.

PeteZO6

It was running fine until you changed the fuel pump and the starter. You had low fuel pressure, how do you know, do you have a fuel pressure gauge on the car? What is the fuel pressure with the new pump?

The starter was really OK, but you didn't realize that until you changed it out and found a wiring problem. Right?

It seems to me that unless the new starter is sucking juice (electricity-amps) from the car, the starter isn't the problem.

How do you know the new fuel pump is working OK? I'd check the pressure and VOLUME of the pump so you can determine whether or not is the problem. I had a similar problem awhile back on my '69 and it turned out to be the fuel pump. One of the valves had come loose from the body and wouldn't allow the pump to supply enough fuel to the carb.


Pete

killervette666

Yes, sorry I didn't clarify! I do have a fuel gauge right in the hard line going to the two fuel bowls. Before installing the new pump the pressure was around 4 psi at idle, now its about 6-6.5 psi.

In terms of the starter, yes the old one was fine, I installed the new one and then figured out that the only thing wrong was that the battery ground strap bolt was loose and thus there was no good ground connection. Don't know if the new one is drawing amps...any way to check without going through an electrical engineering course?

Your right about the volume though, I will check it and see what its pumping.

killervette666

I'd like to add though, that after the work I did on it today, it drives, and when I step on the gas it accelerates just fine, it only starts doing this after idling in gear for a while.

MelWff

If you place you hand over the primary side of the carb when it is surging, does the surge go away? If so, it is running lean possibly caused by a vacuum leak. You set the timing to 18 to 20 BTDC, was this with the vacuum advance connected? The correct way is to set total mechanical advance to 36 and then check what the initial timing figure is. What idle speed are you attempting to set the car for when in drive? Did you adjust the mixture screws with the car in drive?

killervette666

Thanks for all the input!

I think I've pretty much narrowed it down to the fuel pump. After sitting for a little while the pressure will be a good 6.5 psi. However, after I drive it around the block 2-3 times, the pressure drops to 3 psi, and for some reason the float level rise (btw does anyone know why lower fuel pressure causes the fuel levels to rise? at 6 psi it's at the perfect level, at 3 psi the levels go up and the carb starts running really rich). So I'm guessing something is messed up inside the fuel pump.

I try to set the idle to around 750 in park, 650 in gear. I don't set the mixture screws in gear since I'm running a bit of a one man operation, but I will maybe try to do that after getting the new fuel pump.

lars

If your fuel pressure gauge is a liquid-filled gauge, it will change reading as the engine heats up: The liquid filled gauges have sealed cases, so the gauge pressurizes and changes its reference point as it heats up - you can't trust the reading. If it gets warm enough, it will read -0-. Get rid of the liquid gauge (assuming that's what you have) and use a vented non-liquid gauge.

Install a reflective heat shield under the carb. E-Mail me for my BG Installation & Setup paper for instructions.

Lars
V8FastCars@msn.com

thiatt

I would also check ignition. A failing coil will stop working when heated, when it cools it will work fine.

You can test a coil at home its easy. All you need is a multimeter with ohm meter, and a heatgun.
Remove coil from car, attach clips from meter to coil wires. Take reading compare to working range of your coil. Specs can be found online search for your coil specs.
start warming the coil with heatgun careful not to burn it. Watch meter for change if at any time in next five minutes of heating coil goes "out of range" it is bad and needs replaced.

killervette666

Lars-I managed to find a copy of your tuning tips online and will put them to use. I noticed you recommended to keep float levels low for a street car and mine are at the middle marker so I will drop those as well.

Also, thanks for the tip about the liquid gauge, it all totally makes sense now.

I just have one question though, should I not touch the idle-eeze to set the idle speed instead of adjusting the primary and secondary transfer slots? Should I just keep the idle-eeze completely disengaged?

Thiatt-I was also thinking it might be ignition because it does seem to run rougher. I just recently replaced the plugs, the wires are brand new, the distributor is almost brand new (maybe 600 miles on it tops), I will check the coil per your instructions.

71coupe

Some of the better liquid gauges have a small rubber fill plug. If it has one, you can drain it.

blkc3

I had the same issue. I had replaced the fuel pump, carb, cam, etc. I tried using universal fuel line to connect to the fuel pump. It looked fine when I installed. After running a few minutes same issues. Looked everything over about 10 times and discovered fuel line was pinched. I tried to replace with stainless braided hose. - same issue. Looked at a few catalogs, called a few people and I learned the hard way you have to use the molded s shaped fuel line from the catalogs. - hope this helps, sorry to be so long winded.

Doug1

this is good posibility, if it doesn't fix, possibly put old carb(if you still have)back on and see if anything changes.....if runs bad still, then at least you know not to tinker with new carb

Mr.Green

This happened to me once. I thought I had a fuel problem, but after some troubleshooting, the fuel was fine. I managed to diagnose the problem on the side of the road and get a new coil from a nearby parts store. I replaced the coil and was on my way again.

Some other ways to test the coil (I had to get creative with my limited resources):
-Pull out a spark plug and LOOK at the spark while cranking. It should be blue/white. If it's orange, you're not getting enough power, therefore bad coil. If you can't pull the spark plug, put a screw driver in the plug and hold the exposed metal close to a good ground. You should still see the blue/white spark. Word of advice: don't hold onto the metal part!
-Last resort is the shock test. I'll let you figure that one out, but don't put voltage across your heart when doing it.


I hope this helps.

garygnu

also look at proper tank venting .try driving with the gas cap loose.agreed try a new fuel filter.

Hamin79

I had a similar problem a few years ago, turned out to be the ignition module, the car would just die comming off the expressway or at a light, acting like it was fuel starved. Went through all the same things you are right now and i replaced the little black box under the rotor and was good to go