snb73

Just rebuilt the engine and it has the correct new fuel pump from Zip. I have good (4-6lbs) at idle. When I back down the driveway to road test, after 20 feet of a normal takeoff, pressure drops to zero and the vette stalls. Has anyone had this problem before.
I e-mailed Lars about this yesterday, he suggested I check fuel pressure. This seems to be the culprit, but what is causing it? Did I just get a defective pump?


Here's what happened yesterday:

I installed a rebuilt L-82, comp XE268, hooker super comps, and TFS 23*
64cc, and 1.6 ratio rollers. It fired up fine and ran for the initial 20
minute break in period at 2500 rpm. I changed the oil and filterand it ran
fine. No road test yet. I set the timing to 36 degrees, as per your
tutorial. Idle is a little rough, and timing moves a bit at idle. When I rev
it, it seems like the engine takes too long to get back to idle.

When I first road tested it, I went about 1-2 miles and it sputtered and
died. I let it site for approximately 5 minutes, then it fired up for 15
seconds and died. The longer I let it sit, the longer it would stay running;
10 minutes/30 seconds. I took off the air filter and looked into the carb as
I manipulated the throttle. After about two or three full pumps, no more
fuel was squirting.

I checked the fuel filter, it wasnt clogged. Then I removed the fuel line
attached a bottle and turned the engine over. After approximately 3
revolutions, I got about a cup of fuel in the bottle. Fuel pump seems ok. I
reconnected the fuel line, it still wouldnt run. I gave it a little fuel
"charge" through the float vent and it ran like normal. I am assuming I have
a float level problem or something else is not letting the fuel into the
bowl.

Like I said, it will idle all day long. But once I get on it and start using
the fuel in the bowl, it doesn't seem to be replenished.

I also get surging just off idle while cruising, 30mph at 1200-1400 rpm in
second


Here's what went on today:

I borrowed a fuel pressure guage today. I'm getting between 4-5 pounds of pressure, 3-4 at idle and 5-6 above 1500. The vacuum advance is hooked up to "ported" vacuum, not manifold vacuum. It is connected to the port just above the drivers side idle mixture screw.

As a test, I installed a (one) heavier mechanical advance spring. That seemed to help with idling down from rpm's. But it still seems to be taking to long to get down to idle.

I also removes and pluged the vacuum ports for the power brakes and headlights. I wanted to remove that variable.

I had the engine idling and at different rpm's for about 30 minutes, no stalling. This engine has less than 1 mile on it and fewer than 2 hours running. I installed all new componants, including a new stock fuel pump from Zip.

Ok, I just got back from taking it for a road test. The hood is off, and mounted the pressure gauge in such a way that I can monitor it from the drivers seat. The vette started right up, 5 lbs of pressure. I backed out of the driveway, still 5 lbs. I put it in first and started forward, maybe 20 feet, the pressure went to zero. I let it sit for 5 minutes, started it, and got 1-2 lbs.
I poured a shot into the bowl vent to get the vette running. Drove it into the car port, still zero psi.

I checked the fuel lines, they didn't feel colapsed. May be it's a heat related pump failure. The first time I road tested the vette, it was idling for maybe 5-10 minutes and it took about a mile to die. Today I had it running for about 30 minutes and it took 20 feet.

This is wierd. I'm pissed, I want to drive it for more that 20 feet, lol. Do you have any suggestions? Did I get a defective pump?

Thanks, Steve.


[Modified by snb73, 8:23 PM 8/12/2003]

CFI-EFI

You possibly got a bad pump, but probably, not. The fuel hoses aren't collapsing. Are those the lines under the hood? With a mechanical fuel pump, the lines to the rear of the pump operate at a negitive pressure. From the pump forward, thay are under pressure. Could one of the hoses at the tank or to the rear of the pump be collapsing? How about a kink in one of the steel lines? A clogged in-tank fuel strainer? An excess vacuum build up in the tank? Is the fuel return line hooked up and working? Tank properly vented? Despite the tuning adjustments, you obviously have a fuel delivery problem. All the above could be causes, as, of course, a bad fuel pump. My bet is against a bad pump. Good luck, and...

RACE ON!!!

snb73

Thanks CFI-EFI,

I had the same problem with the cap removed. I too thought it might be vacuum lock. All the rubber lines were replaced.

I found the problem, a clogged fuel sock. I used a two foot long rod and tapped the sock, in an attempt to loosen any debris. Road tested the vette and it ran for about 5 minutes before clogging/loss of pressure. I removed the sending unit and could barely see through the sock.

I removed it , temporarily, and road tested. No more problems, fuel pressure is 7-8 lbs on start and 5-6 lbs after warm up. A new sock is on order.

Thanks Steve.

CFI-EFI

I'm glad you found the problem. Besides changing the sock, you ought to consider cleaning the inside of that tank. Good luck, and...

RACE ON!!!


[Modified by CFI-EFI, 6:25 PM 8/14/2003]

71coupe

Are you sure the timing chain is not off a tooth? That cam will run rough when cold, but if you snap the throttle it will be quick to rev.
As far as the fuel pump, pressure will drop when velocity increases. It's probably ok

EDIT - just read the post that says you found the problem - I really need to start reading posts fully before a reply :cheers:


[Modified by 71coupe, 12:02 AM 8/16/2003]