[THEGTOCHISM]

I am working on a 1967 execuitive, 400 cid , With a rochester 2 bbl. It jumps off the line fine for a couple of seconds then bogs then catches up , or it cuts off. Not a drag racing start .just normal stop light stuff. The timing chain and gears are new. fuel pump is new as well as all rubber fuel lines. Tank sending unit is new with new sock. Timing is set at 10 deg advance. Ported vacume through the card mounting stud [RR][ New vacume advance ] timing connected is at 28 deg. -idles fine. Total in is 40 advance. I have had this carb off so many times i am about to put zippers on it. It pumps as soon as you just move the arm. Nice squirt. Anybody got any ideas?

[Tripower455]

Float too low?

[Bronze66]

If your timing numbers are correct then you only have 22* max mechanical advance, plus the 18 vac = 40*. That's a tad low. Something you might want to look in to. As far as your carb you may have dirt/gunk restricting the idle tubes. They are use for idle,transition to main jets and at cruise. You transfer slots could be plugged/restricted. Or you may have the idle set improper. Only about .020 of the slot should show under the throttle blade. If more shows then the transfer slot doesn't get to pass enough fuel when your going to the main jet system. Your jets could be restricted also with gunk. Have you taken the carb off and looked at it? Is this the carb that was on it before the other work was done? If your vac is hooked to the base stud then you have full manifold vacuum. Which is correct . It could be as simple as adjusting your accelerator pump arm. I believe it should have around .100 preload on it in the idle position. I'd look at that first. do some checks and get back to us.

[THEGTOCHISM]

This cab was removed and soaked overnight and cleaned . No dirt or anything i can see. All holes blown out with 175psi air. vacume reading is connected to the base carb stud. but it is the same if you connect it to the rear of the carb. The accelerator pump gives a nice squirt the entire length of the working of the arm. Even made sure the wire ring was transfered from under the old pump to the new to help it seal good against the pump well walls. I have had this carb off at least 8 times. usually this sort of thing is in the pump. like i said it moves as soon as you give it gas then bogs and cuts off. So you think 40 deg. Total timing at 3500rpm is too low?

[THEGTOCHISM]

checked float it is on the money

["QUICK-SILVER"]

The spray pump is making it jump but your not getting fuel up and out of the boosters for it to go. Power valve not working properly would definitely be something to look at.
The actuating rod/piston that opens and closes the power valve works off vacuum. A vacuum leak on the top gasket will stop the actuating rod from working.
The boosters may not be seated properly. The gasket under the boosters could be leaking. Pickup tubes under the boosters stop up easily and are hard to clean.

All passages need checked to see if fuel can go through them. Fuel through the jets goes to the idle circuit and the run circuit/boosters. Additional fuel for acceleration comes from the power valve.

Engines don't run on spray pumps. You've got to get the rest of the carburetor working.

[THEGTOCHISM]

The power valve is something to consider. the piston is free i did check that. Are you saying a leak at the top of the carb gasket will stop that power valve from working? I had re-checked the booster gasket. even added a second one i had, no change. i know is in the transfer circuit somewhere after the initial pump shot. just not shore where. I found someone had changed one of the weights under the rotor button. They had one larger than the other and when the rotor was installed it locked the timing in a advanced position. Corrected that with another set i had. That really helped. But not this carb. This 67 400 has a carb and intake with a choke tube. Yet my 66 gto [389] and my sons 68 gto [400] both have divorced chokes. It that correct for a large car? This is a one owner car. If all else fails i have another 68 2bbl intake and a known good carb i could put on it and file 13 this set up. I just hated to loose the original carburator.

["QUICK-SILVER"]

THEGTOCHISM,
The actuating rod for the power valve hangs down out of the carburetor top. There is a vacuum passage way through the top gasket, thats what makes the rod move up and down, working the power valve. If the rod is bent and not touching the power valve pin, the power valve will not open. If the rod is sticking in the up position it will not open the power valve. That rod must operate freely, it is spring loaded.
Get casting number and date off your intake, also carb number, then will be able to verify if it's correct for your motor. May need some motor #s too.

[Schurkey]

Originally Posted by THEGTOCHISM

Timing is set at 10 deg advance. Ported vacume through the card mounting stud [RR][ New vacume advance ] timing connected is at 28 deg. -idles fine. Total in is 40 advance.

PORTED vacuum through the carb stud???

Originally Posted by Bronze66

If your timing numbers are correct then you only have 22* max mechanical advance, plus the 18 vac = 40*. That's a tad low. Something you might want to look in to.

Originally Posted by THEGTOCHISM

So you think 40 deg. Total timing at 3500rpm is too low?

Do I have this right? Initial timing = 10 degrees. Vacuum advance = 18 degrees. What you're claiming is "total timing" is 40 degrees @ 3500--but you haven't removed the vacuum advance from that figure.

10 (initial) + 18 (vacuum) =28 degrees. 40 degrees - 28 degrees = 12 degrees of centrifugal advance? That doesn't make sense. Most distributors have WAY more than that.

"Total" timing DOES NOT include vacuum advance. You're running that engine with 10 (initial) + 12 (centrifugal) = 22 degrees of total timing? I'm surprised it doesn't run warm.

I'd expect it to run best with ~32--37 degrees of total timing (Initial + centrifugal) PLUS as much vacuum advance as you can get by with and not have part-throttle ping.

Initial + Centrifugal + Vacuum can often add up to 55+ degrees of advance--but the only way most engines would actually see that much advance is if you were engine-braking down a steep mountain grade (High RPM and high vacuum don't usually happen at the same time.)

I'd like to see you pull off the vacuum advance hose and tell us how many degrees of advance you have at ~3500--4000 RPM. (and the RPM that it stops advancing.)

[THEGTOCHISM]

Let me put it another way. Vacume advance disconnected and plugged .At idle timing is set +10deg. Re connect vacume advance to right rear carb ported stud [ac cars and try powers in 66 used this stud that is drilled for vacume] Rev the engine to 3500 rpm and use my dial back timing light it shows 40 deg advance. Now it may pick up 3to 5 more if i rev it higher but i don't want to take a chance and do that. Is 40 deg too high? I know smog engines take a lot od timing with their HEI dist. But this is a points dist.

[THEGTOCHISM]

i did re check the power valve and the rod is not bent and moves freely. What i ended up doing was i had another 2bbl on a 68 lemans that worked fine. Problem was 68 has a divorced choke. same as my 66 gto. The 67 exect. has a choke tube. I swapped manifolds and carb, and put a new kit in the carb. The hesitation is now gone. I have a feeling there was a restriction in the feed tube to the boosters. It will burn the tires off of it now. Hurray!!

[Schurkey]

Originally Posted by THEGTOCHISM

Let me put it another way. Vacume advance disconnected and plugged .At idle timing is set +10deg.

Your initial timing is 10 degrees advanced. Yup.

Originally Posted by THEGTOCHISM

Re connect vacume advance to right rear carb ported stud [ac cars and try powers in 66 used this stud that is drilled for vacume]

That's not ported (timed) vacuum. That's manifold vacuum. And it may work just fine. This is a terminology issue, not a functional one.

Originally Posted by THEGTOCHISM

Rev the engine to 3500 rpm and use my dial back timing light it shows 40 deg advance. Now it may pick up 3to 5 more if i rev it higher but i don't want to take a chance and do that. Is 40 deg too high? I know smog engines take a lot od timing with their HEI dist. But this is a points dist.

Re-do this test but DO NOT connect the vacuum hose to the distributor. I want to know what the maximum advance is WITHOUT the vacuum advance functioning. Maximum advance without the vacuum should be ~32--37. I have every expectation you have NOWHERE NEAR enough advance--and--it should probably come in sooner than 3500 rpm. But let's just deal with the amount of advance, not the speed it comes in (for now.)

Whether or not that's causing your bog--I don't know. You'll pick up fuel mileage AND power by advancing the timing, though.

["QUICK-SILVER"]

THEGTOCHISM,
I hope you're going to dig in that old carburetor and let us know whats in it.
I cleaned out a carburetor for a friend this past winter. I told him it probably had a bug in it. Didn't find a bug but found one of its legs.