427/435 idle speed

[Roger M.]

I have both a 67 and 68 427/435 that have the same problem. They idle, normally about 800 rpm for 10 or 15 minutes, then will drop to 3-400 rpm and eventually die. (they'll start back ok) I've tried the Vac adv, timing, carb adjustments, nothing seems to work. Anyone have any ideas?
Roger

[Mike F.]

Re: 427/435 idle speed

Both cars having the same mechanical problem would be pretty rare.

Are the chokes working/set correctly?

On a cold start with the choke set, what is the idle speed right after ignition? Without touching anything, what does the idle speed do (choke still set) as the engine warms up? Have you adjusted your choke idle speed and non-choke idle speed seperately?

(With the choke set, my 70 350 cold starts at 1000rpm, as the engine warms (without touching anything) the rpm will increase to about 1600-1800rpm. After the choke fully warms and is completely off, the car will idle at 800rpm.)

http://www.lbfun.com/warehouse/tech_...ower_setup.pdf

[Ken A.]

Re: 427/435 idle speed

The center carb is used for idle and you probably exposed too much of the transfer slots trying to get a satisfactory idle. Make sure the 2 end carbs are not open. The simple fix is to enlarge the brass idle circuit plugs in the metering block by 2 drill sizes. You will need a 60-80 drill set & a pin vise. Check the holes with a bit that fits & then go up 2 sizes & drill out the plugs. Clean everything up & reassemble using the correct parts kit & you're good to go. It will be a little rich, but will idle for hours at 700-800 RPM.

[Roger M.]

Re: 427/435 idle speed

Mike,
The 68 with choke on idles at about 1200 rbm and drops back to about 800 as it warm up. Have not adusted the two separately
Thanks for your input

[Roger M.]

Re: 427/435 idle speed

Thanks for the input, I'll give it a try

[Timothy B.]

Re: 427/435 idle speed

The center carb is used for idle and you probably exposed too much of the transfer slots trying to get a satisfactory idle. Make sure the 2 end carbs are not open. The simple fix is to enlarge the brass idle circuit plugs in the metering block by 2 drill sizes. You will need a 60-80 drill set & a pin vise. Check the holes with a bit that fits & then go up 2 sizes & drill out the plugs. Clean everything up & reassemble using the correct parts kit & you're good to go. It will be a little rich, but will idle for hours at 700-800 RPM.

I don't agree, if you have original # carburetors and metering blocks the last thing I would do is start drilling little brass restrictions without knowing exactly why you are doing that. Enlarging the idle feed restriction will richen the idle mixture but affects the off idle A/F ratio calibrations.

When the idle slows and engine dies is the engine rich like it's getting to much fuel? After the engine warms good try the emulsion screw adjustments, you should be able to kill the engine by turning them in and max vacuum at idle should be anywhere from 3/4 turn out to 2 turns out.

[Tim S.]

Re: 427/435 idle speed

Does the problem change when placing a hand over the top of the carb? I recently experienced the same problem on a friends 67 435. He had a set of reproduction Holleys on the car. After chasing the issue for 2 years, a set of properly restored originals handled the issue. Night and day difference in how the car ran overall.

The only thing we could think of was the base plates were affected too much by heat? BTW, we went through the whole deal with checking the slots, proper base gaskets, etc, etc. We were told after all of this, the castings for reproduction carbs do not measure up like they should.

I have provided a link to the fellow I have been using for my carb work. I am nothing short of satisfied.

http://www.vintagemusclecarparts.com/index.php

Hope this helps!

Tim

Tim