Why do I have high fuel pressure...

[1795]

Originally Posted by patrickt

The way I do it (no jokes please) is to put a paper towel under the boosters and then put my mouth on the vent tube and blow down through it. Gas flows right out the boosters and drops the level quick as a flash. Easiest and quickest way I know.

Patrick,

I cannot quite picture that process. Would you mind making a youtube video of that and posting it for us?

Seriously though, you do have a good ability to figure out how to address problem when confronted with them. Now don't let that go to your head.
:roll eyes:

Jim

[steve meltzer]

Patrick, i agree with Jim. Maybe post on one of the porn sites? Perhaps entitled, "Holley does Dallas"? s

[patrickt]

... precisely why I have not posted this little carb tip previously.

[steve meltzer]

it's been awhile and the Cobra is still sitting, waiting for its place in line. in the meantime, can you help with the 4160 on my '67 'Vette. I believe this started when I pulled the carb to fix a leak on the secondary side, but I'm not sure. I also replace the throttle/acceleration rod. New gaskets, sl change to the vent rod (on the primary bowl), which somehow got bent a bit. No other changes.

Doesn't leak, and the car runs great in all aspects, except if/when you "slam" the accelerator at idle. Then it stumbles and usually dies. I cleaned the pump squirter in lacquer thinner and blew it out with compressed air. It looks like there's a good pump shot if you just "flick" the accelerator rod or the arm, but not if you do it suddenly and with the force of "slamming your foot down on the go pedal". Then the shot is poor. Floats are perfect.

Timing is spec (base=10° BTDC) and the vacuum can works fine with a Mity Vac and, visually, with a timing light, it advances under acceleration. New dizzy cap.

I have not replaced the a-pump as I'm not convinced it matters, but should I? Would advancing the timing help? thanx. steve

[patrickt]

I would first check the accelerator pump. You have a 30cc pump in your 4160, which should be squirting a volume of 3cc on each good full stroke of the pump. So, run your car for a minute or so to get the front bowl nicely filled, then shut the engine off. Tuck a sandwich baggie (or some other suitable receptacle) around the squirter, get back in the car, and with the engine OFF give the accelerator pedal five nice, hard pumps to the floor. Pull the baggie of gas back out, trying not to spill it, and pour it in to your graduated cylinder. If you don't have 15cc's of gas in there then repeat the test. If you consistently fail this test, then you've found the problem and we'll figure out what's broken on that circuit.

[patrickt]

... and if you have the orange cam in there, which is what I think you probably have, since it came stock, then anything under 12cc or so is going to raise a flag. Different cams, and screw hole 1 or 2, will give us different results, but we'll just check your output with one of the Holley charts and see if you're at least in the ball park for volume. But if you've got a different color cam in there, let us know.... I'd really just like to see it come back abysmally low.

EDIT - Here's a handy chart that tells you what volume you can expect from the different cams and positions.

[steve meltzer]

It's technically tough to catch all of the effluent in the experiment, but I tried hard, 3X. Biggest volume I could capture on 5 pumps was about 6cc...so, about 1.5 cc/ pump. The cam is maroon/brown and in position #1. thanx. s

[patrickt]

Originally Posted by steve meltzer

It's technically tough to catch all of the effluent in the experiment, but I tried hard, 3X. Biggest volume I could capture on 5 pumps was about 6cc...so, about 1.5 cc/ pump. The cam is maroon/brown and in position #1. thanx. s

The maroon/brown cam is a big cam. http://documents.holley.com/pumpcamgraph.pdf I think there's something wrong on the accelerator pump circuit. Shooting from the hip, it's going to be one of these:
1) The linkage is screwed up and the cam lever is not getting pushed down right to actuate the pump;
2) The little orange umbrella seal is leaking, so you're not getting a good squirt in the right direction, or the diaphragm is worn out, or the spring is broken or missing (elves do that);
3) There's a clog in the passageways from the pump to the nozzle;
4) The nozzle area is mucked up preventing a good squirt. You know there are two gaskets and that little plumb bob thingy that go under the nozzle. If you remove the nozzle and take it away to clean it, elves always sneak in your garage and hit the throttle, making the little plumb bob fly out and disappear. Are you absolutely positive it's still in there?

[steve meltzer]

Originally Posted by patrickt

The maroon/brown cam is a big cam. http://documents.holley.com/pumpcamgraph.pdf I think there's something wrong on the accelerator pump circuit. Shooting from the hip, it's going to be one of these:
1) The linkage is screwed up and the cam lever is not getting pushed down right to actuate the pump;

I think this all will be easier to diagnose with the carb off the car. Agree?

2) The little orange umbrella seal is leaking, so you're not getting a good squirt in the right direction, or the diaphragm is worn out, or the spring is broken or missing (elves do that);

With the carb off the car, i might as well replace the diaphragm. How do you tell if the orange umbrella is sealing the vent? is it supposed to be flush with it?

3) There's a clog in the passageways from the pump to the nozzle;

That's in the metering block, right? Soak in carb cleaner or ??

4) The nozzle area is mucked up preventing a good squirt. You know there are two gaskets and that little plumb bob thingy that go under the nozzle. If you remove the nozzle and take it away to clean it, elves always sneak in your garage and hit the throttle, making the little plumb bob fly out and disappear. Are you absolutely positive it's still in there?

I call those "Jesus" gaskets/washers, 'cause you'll always say, "Jesus" where are those %$*&^&*&^ things! (no disrespect meant!)

thanx. steve

[Gaz64]

Steve,

Are you sure the pump cam is brown, and not a discoloured white, orange, red etc?

The brown and yellow cams are meant for Dominator 4500 carbs, which have a larger throttle shaft.

Gary

[patrickt]

The brown cam is the Tyrus of Holley Accelerator Pump Cams. Here's a pic:

[steve meltzer]

Point well taken, and, I was in a hurry. I'll pull the carb off the car (the nth time) and then I can get a great look, etc. Got some work (tho' generally fun, challenging and interesting) in front of me. Always something with these old cars. s

[steve meltzer]

OK, took the carb off the car and here are a few of the things I found:

1) the cam is def'n a red part #240 which, as was pointed out, is probably wrong for my carb. (no damn wonder my sox never match!)

2) I have some orange ones and a cream colored one. need to check the numbers.

3) The gasket at the bottom of the accelerator pump mechanism was torn.

4) As seen in these photos, the gasket that I have that interfaces between the carb body and the metering block was missing two orifices, so i just poked a hole in the gasket. As you can see, it's not very good. I just fixed this with a real punch, and it looks fine now (not in the photos). Not sure of it's importance in the circuitry.

[patrickt]

Originally Posted by steve meltzer

As seen in these photos, the gasket that I have that interfaces between the carb body and the metering block was missing two orifices, so i just poked a hole in the gasket. As you can see, it's not very good. I just fixed this with a real punch, and it looks fine now (not in the photos). Not sure of it's importance in the circuitry.

Uhhhh, no. That hole is always there on the main body, but it's only used when you have an auxiliary idle air bleed, which you don't. I don't think punching a hole in your gasket will make a difference one way or the other though, but test it out by putting a small straw in the hole and see if you can't blow through it. IOW, I think that's a dead end hole that does nothing. Try using the orange cam and use hole #1.

[steve meltzer]

I'm sucha moron! thanx. orange cam it is. more later when i get the delicate gasket for the A/P. thanx again.s

[Gaz64]

The metering block gasket does not need any holes as Patrick has mentioned.

Your accelerator pump diaphragm was torn? It would have had a fuel leak as well.

The red cam in pos 1 is just short of the orange cam in pos 1.

Nothing wrong with the red cam if it suits the engine tune.

The white cam is the smallest in delivery at any change in throttle angle.

Gary

[steve meltzer]

Originally Posted by Gaz64

The metering block gasket does not need any holes as Patrick has mentioned.

Your accelerator pump diaphragm was torn? It would have had a fuel leak as well.


The red cam in pos 1 is just short of the orange cam in pos 1.

Nothing wrong with the red cam if it suits the engine tune.



The white cam is the smallest in delivery at any change in throttle angle.

Gary

NO, i just explained it wrong. At the bottom of the nozzle/squirter is a small ? 1/4" gasket. it's torn. pump diaphragm is fine.

I've used that red cam for years, and the car ran great. I'll bet it's either the torn gasket or the vent rod was bent sl. out of whack. thanx. s

[patrickt]

Originally Posted by steve meltzer

NO, i just explained it wrong. At the bottom of the nozzle/squirter is a small ? 1/4" gasket. it's torn. pump diaphragm is fine.

I've used that red cam for years, and the car ran great. I'll bet it's either the torn gasket or the vent rod was bent sl. out of whack. thanx. s

Right, there's actually two gaskets for the squirter. AND, the plumb bob thingy. That's still there, right?

[patrickt]

I looked it up. It's called the Accelerator Pump Nozzle Check Needle. Gaskets go both above and below the squirter.

[steve meltzer]

correct. the lower of the two is a soft, flimsy gasket, the one between the Phillips and the squirter is really more like concave thin metal washer. Right? s

ADD: yeah, and there's the plumb bob thingy that looks like some needle and seat combos.