New carb and itake - running ruff

[Jimbotronics]

I just got my intake and 600 cfm holley installed. Idles nice and runs out great at smooth acceleration, but if ya hammer down it spits spurters hacks and coughs and gradually goes. Timing is a little advance but very little. Is it how the carb is adjusted or could it be something more like a faulty fuel pump? By the way the engine is an '87 350 with HEI.

[Jimbotronics]

ttt anyone?

[neonlarry]

This is some info I found on another site. Be aware it is about a Q-Jet but principle is the same disconnecting the accelerator pump will be different.

by Lars Grimsrud
"How can you tell if an off-idle stumble is caused by a lean or a rich condition?
A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. To narrow it down, tap the roll pin out of the accelerator pump lever by using a small pin punch or a small finish nail. I actually use a small, broken drill bit that's just the right size. Using a hammer, gently tap the roll pin in towards the choke air horn wall. Don't jam the pin right up against the wall: Leave just a little bit of a gap so you can get a screwdriver blade in between the wall and the pin to pry it back again. With the pin tapped out, remove the accelerator pump lever. I like to do this with the engine running so I won't have any trouble starting the engine without the accelerator pump. Now, rev the engine a little with the throttle. Notice if the engine seems quicker and more responsive, or if the hesitation & stumble is worse. If the engine actually feels more responsive with the accelerator pump disconnected, you have a rich condition. If the hesitation is worse than before, you have a lean condition. If there is no change whatsoever, you have a non-functional accelerator pump.

To verify a suspected lean condition after this test, simply hold your cupped hand lightly over the choke air horn area with the engine running at idle, restricting the air flow. If the idle speed and idle quality momentarily increases, you have a verified lean condition. You need to select a jet/rod combination that will give you a little more Cruise Metering Area. Make these changes in less than 10% increments using the Figures provided in this paper."

Timing can also cause off idle stumble. How or more exactly where do you have your vaccum advance ported?

[cableguy0]

most likely your problem lies in the carb. you either need to get a bigger accelerator pump nozzle or have yours drilled a size or two bigger. timing can also cause this problem. try messing with the timing first. do you have a timing light? if not you should invest in one makes life a lot easier to not have to guess where the timing really is

[Jimbotronics]

Yup, I have a timing light and will double check it tonight - It was just done by ear when the intake was changed out. The vaccum advance hose should be removed when setting it too right?

Neonlarry - not sure what you mean by "where they're ported" -

[neonlarry]

Do you have it on the manifold or on the carb and if on the carb is it above or below the throttle plates?

[Jimbotronics]

It's on the carb - I want to say below the throttle plate but I'll have to double check this afternoon when I get home.

[Jimbotronics]

I didn't install the intake and carb I had it done - so now I need help in figuring out what's what - Here's what I see, vaccum advance from the distributor is going to the bottom of the carb (was going to the top which is now plugged made a little difference but not much). There's a 5" tube connecting a port to the left of the automatic choke to a port directly above the choke. Why would there be a tube connecting the carb right back to itself? I disconnected the vaccum advance and set the timing dead-on. Runs great from and idle - but crappy if you really giver.

[Jimbotronics]

Gonna try to add a photo - you may have to cut and paste.

[rage'nrat638]

make sure your vacuum advance is pulling in....hook up a hose to it and apply
lite suction.....suck on it....

[Jimbotronics]

LOL - I didn't like how that sounded!

Yup it's pulling in. Engine idles up when the hose is removed from the carb and then idles back down to a smooth idle when replaced.