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ducrider123 09-02-2012 11:27 AM

Hesitation problem pontiac 400
So, I will start off by saying what problem I have.

I just recently rebuilt the Pontiac 400 in my 67 bird. The engine is new to me, so I never heard it run. I am havng a bog/hesitation issue when I step on the throttle. If I step on it hard from idle it barks through the carb and sometimes will die or stumble really bad until I take my foot out of it. If I step on it easy it hesitates then it will pick up.

I have tried everything from an Edelbrock 600, avs 650, and a Edelbrock 750. The easy on throttle hesitation get worse with a 750 carb. I have been sticking with the 650 AVS as of late. I have gone rich, lean, way rich, and way lean. No change.

I have set the timing everywhere for 4 to 14 degrees on the HEI. I moved the vac advance from ported to no ported no difference. I think vac advance it a 15".At idle the vac is 10-14 in wc. and 20-22 in wc at 2500 RPM on the un-ported port on the carb. I had the distributor set up on a Sun machine. I do have a brand new dist. but not the availability to the Sun machine anymore.

The engine has been completely gone through. It has been bored .030 over. It has Icon pistons. (IC891 Pontiac 400 14cc dish). The heads are #16. Redone but not ported. Edelbrock Performer intake. All gaskets are Fel-pro. New balancer. The cam is a Summit SUM-2801. I can give the specs if needed. Stock lifters and 1.5 roller rockers. the torque converter is a 2000-2200 stall.

On thing that I have noticed is when you are watching the timing and you open the throttle at the carb the timing goes towards '0" for a second then
it retards. I don't know it that is normal?

Any help would be great with the . I am in the process of rebuilding a Q-jet but I don't think that is going to solve my problem. Also I have a engine vibration at 2700 RPM. By that I mean it's the worst at 2700 it smooths out above and below.

LATECH 09-02-2012 02:06 PM

Sounds like 2 problems.
I would say you have the base or initial timing set wrong and or / the distributor advance weights are sticking also.
Check the mechanical weights to be sure they move freely. Then Unhook the vacuum advance, set timing at 12-14 degrees, then be sure the engine speed is at 650 or less after you set the timing. If it is faster, then turn out the base Idle screw to slow it down and recheck the timing.
Also Is the accelerator pump squirting as the throttle is cracked open?
Are you sure the carb has the correct float setting?
Are the Idle air bleed screws at about 2 turns each?

ducrider123 09-02-2012 02:16 PM

I have it set at 13 right now, vac uhooked. I haven't pulled the distributor cover yet, but everything was cleaned, new curve kit installed, and lightly greased under the plastic bushings. I will pull it and see if everything is free.

accelerator pump works, I tried all settings, no difference.

I checked the float a 7/16.

2 1/4 the bleed screws areout.

ducrider123 09-02-2012 03:06 PM

he are a couple of other things.

with the 750 carb on it I smell rich exhaust.

I tried locking the secondary air shudder open and closed, also no difference.

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