C2 still won't idle properly

[John P.]

Hello all,

I am looking for further suggestions for my 327/350 1965 convertible. I brought this up a while back.

The carb is a replacement 600 cfm Holley, bought new a couple of years ago. My main problem is idle that sits around 1000 rpm.

I did disassemble and recenter the valves in the bores, polished them a bit-no real change. I replaced the throttle spring, added a second spring. No change. I checked where the bores closed-seems to be correct, according to the photos provided here on the forum by a member.

Just looking for ideas where to go with it next. The engine runs well, idle seems to be only issue. Thanks as always.

[Larry M.]

Re: C2 still won't idle properly

I would check the setting on the secondary throttle plates adjustment screw. It keeps the secondary plates open a bit to keep gas fresh in the secondary fuel bowl. But if set too far out, it overrides the idle setting(s) of the primary side. I believe carb needs to be removed from car to access screw to make this adjustment.

After rebuilding carb and resetting this screw on my #3810 carb, I noticed that idle mix and idle speed adjustments on the primary side did not make as big an impact as. previously. So I need to back this screw adjustment down a bit for my own car.

Having said all that, I like to set the curb idle at 900 RPM on my 67 327/350 HP car. Car seems to run smoother and respond better from a dead stop.

Larry

[Bill B.]

Re: C2 still won't idle properly

John,

Are you sure that the throttle cable itself is returning all the way with some slack at the primary throttle shaft assy?

[David H.]

Re: C2 still won't idle properly

John

re Vacuum can on your distributor. High idle with VC disconnected and carburetor port plugged?

Is distributor vacuum hose connected to port or manifold vacuum?

Initial distributor advance timing value (everything disconnected and plugged)?

Dave

[Keith B.]

Re: C2 still won't idle properly

vacuum leak?

[Owen L.]

Re: C2 still won't idle properly

I would check the setting on the secondary throttle plates adjustment screw. It keeps the secondary plates open a bit to keep gas fresh in the secondary fuel bowl. But if set too far out, it overrides the idle setting(s) of the primary side. I believe carb needs to be removed from car to access screw to make this adjustment.

Certainly a lot of things to check in all of the replies above: timing, vacuum, and accelerator rod return will certainly affect idle speed. As a matter of variables, disconnect (and plug/cap) the vacuum port and remove the accelerator rod from the linkage. Then the idle is only affected by the carb settings. (Even with misadjusted timing, as far as I know, you should be able to kill an engine with closing down carb idle.)

The secondary setting is done after the primary. Once you set the primary according to the idle transfer slots, hold the carb up to a light source and adjust the secondary closing plates to mimic the gap you see in the primary plates. This is according to an article that I believe Duke and Lars wrote and it worked great to cure my high idling Holley.

Once you can get the idle down to about 500-600rpm then you can reconnect the vacuum advance and make further adjustments knowing that the carb is capable of idling down.

[John P.]

Re: C2 still won't idle properly

timing 12 degress BTDC no obvious vacuum leak. Idle drops when VC disconnected and plugged. connected to manifold not port.

Perhaps I need to find the adjustment for the secondaries and work on that. I centered the plates but did not look to adjust the screw.

[Owen L.]

Re: C2 still won't idle properly

What is your idle rpm with the vacuum advance port on the carb blocked? If you can get it down to 500-600 using the idle adjustment screw, you shouldn't need to pull the carb again to adjust the secondaries. If not, then the secondaries are where to look next. If you go the route of comparing the light gap to the primaries, err on more closed than more open; that will place the adjustment burden on the primary screw.

[John P.]

Re: C2 still won't idle properly

I'll check I suspect it is 500 or less Seems close to a stall

[David H.]

Re: C2 still won't idle properly

John

Have you investigated Holley's Tech Resources on their web site? Link below.

Dave


Here Is The Correct Procedure For Setting An Optimized Idle Mixture And Speed - Holley Motor Life

[John P.]

Re: C2 still won't idle properly

I have looked at this and other resources. But I will sift through the process again. Seems to be a simple adjustment that needs to be made.

[Timothy B.]

Re: C2 still won't idle properly

John,

If it's a vacuum secondary carburetor the best way to set the rear blades is to back the stop screw out and shut the blades then after the screw makes contact turn it only 1/8-1/4 turn. You will feel the blades stick in their bores but when the stop screw makes contact they will move open from the closed position freely. Keep them closed to where they just don't stick in their bores, if not the vacuum diaphragm will not be able to open them.

Set the idle speed using the primary idle speed screw, if your camshaft is stock you should have no problem doing this. What type of PCV valve are you using with this carburetor? The factory 1965 set up used a fixed oriface PCV approx .095 diameter hole.

[John P.]

Re: C2 still won't idle properly

i believe that is the one I have