When my 67 BB gets good and warm she won't idle at a stop light.

[John M.]

So after I drive the car for a good 30 mins plus she won't idle normal at stops. When I first take her out she runs perfect then after running it for sometime she starts to choke at the lights. It will run hard at any constant speed until she comes to a stop, then I've got to keep my foot on the gas lightly to keep it from stalling. I guess I need to start at square one again on trying to get her timed correctly.

I'm bringing the car to orlando to the NCRS show to have a top installed by Coffman, by anychance is there someone who can take a look at her?

[Gerard F.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

John,

That sounds more like a carb thing. Maybe a vacuum leak at the primary carb or the quality of the gas. Try tightening the mounting bolts at the carbs.

I'm a S/B 67 guy but had the same problems. Turned out that the carb base to manifold gasket was leaking vacuum. Would stall out at a light after a hot run. Percolating.

Might be something else, but worth a try.

[Dale C.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

I had the same problem and tried everything. I think it's the darn gas we get today. Mine does better on race gas, about 117 octane. I cut the ratio down to 50/50 with good stuff at shell. Still don't like anything about ethonal in our gas. I hear avgas works also.
Dale

[Larry B.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

When it has the problemlook down the carb you should not see any fuel going in.If you do you probally have a bad power valve. Also be sure to check the float levels even with the bottom of the sight glass plugs.

[Duke W.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Could be a number of things - fuel percolation, vacuum leak. Put a vacuum gage on it and look at the initial timing and idle speed and vacuum (neutral on a manual, Drive on an auto) . Tell us the numbers. You didn't tell us what engine. Some '67 engines have ported vacuum advance, some are full time. So...

Is the engine OE configuration or modified - like a different cam? What transmission?

Check that the VAC and any other vacuum devices holds vacuum. You can mitigate percolation by wiring the heat riser valve open and converting ported vacuum advance to full time, but that might require a different VAC.

We need more information.

Duke

[Timothy B.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

John,

If the engine is in good tune and there is no detectable vacuum leak then there may be a internal vacuum leak in the carburetor causing the engine to suck gasoline. I assume the engine has a Holley carburetor, these carbs are modular so they can leak internally at the gasket surfaces.

Can you provide more information like what work has been done on the engine lately.

[John M.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Its L68 427/400 auto trans the car runs perfect at any speed as long as she is getting gas she is good to go.

[John M.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Well the car has been in restoration since 1977 its the original engine and holley carbs. I found reciepts that the carbs were rebuilt, she starts right up and runs perfect until in gets ran hard. I'm going to check out the vacuum as suggested but my gut is telling me its still just a tuning problem. I'm bringing the car to the Orlando show to get a top installed so I was hoping after the top I could hook up with someone who can take a look at her.

[Hebert K.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

There is a web site that lists gas stations that sell ethonal free gasin the U.S. and Canada
The site is http://pure-gas.org/

[Duke W.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Do you have a timing light and Mity Vac or a simple vacuum gage?

Can you do the checks I suggested in post #5.

Do you have a CSM or otherwise know how to do the idle speed/mixture adjustment procedure?

Duke

[Stephen L.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Had a similar problem with an L36. During engine rebuild I had painted the surfaces of the heads where the intake sits. I did a hell of a job on the paint... nice heavy coat. After the engine was warmed up the paint softened and produced a vacuum leak. Just wouldn't idle below about 1500 rpm. Used a little water along the intake gasket and the water rapidly disappeared. Cleaned off the paint and I was good to go.....

[John M.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Duke I've had that skill set in the early 80's however at this time I'm not 100% confident that I 'm doing everything correctly. I did get this car in boxes and I do have her back on the road so I'm not hopeless however I've got to get better with the timing and tuning steps.

[Richard M.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Hmmm....400HP tripower with a Powerglide. It's likely still ported vacuum. Does it have Air Conditioning? Has it always been a problem as you described, or did it happen after a time of running well?

As Duke recommended I'd agree that you need to get a vacuum gauge on there and do the checks. If you have a vacuum leak it could be the vac advance can or the modulator valve on the transmission, or a leak/crack in one of the vacuum lines. If you have A/C that adds more suspect lines and gadgets as well.

I'd eventually switch to manifold vacuum, but you need to measure vac with all ports disconnected so you can select the right vacuum advance can using the 2 inch rule.

There will be plenty of knowledgeable guys in Kissimmee, but they may not have all of the tools on hand to check it out effectively for you.

Rich

[John M.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

It does have factory air, I have the compressor on and belt but I have not installed the lines and serviced yet. It has the original Mod valve installed, I only have about 900 miles on her since getting it back on the road.

[Duke W.]

Re: When my 67 BB gets good and warm she won't idle at a stop light.

Set the timing and go through the idle speed/mixture adjustment procedure. There should be a step-by-step procedure for both in the CSM. Download the AMA specs from the GM heritage site as it may have additional info.

The idle speed mixture must be set with the engine idling in Drive with correct initial timing, and the recommended speed should be in the CSM and AMA specs. Be sure the parking brake is firmly engaged and double chock at least one front wheel.

I've been looking for some time for reliable data on manifold vacuum for an OE big block with an automatic set up properly idling in drive.

Does your engine have an OE equivalent camshaft? If not, then you're on your own to figure out how to make it work.

I'd also like to know if your engine has full time or ported vacuum advance.

Duke