69 427/390 and 2200 RPM cold idle for PV

[Gary H.]

I am having some issues getting my car to idle up to the required 2200 rpm (L36 4 speed) specified by the PV manual. I have the idle screw in as far as it goes and cant really get the car to idle above 1800-1900 rpm. It is humid and about 70 degress out in the mornings here in south Florida and this is the winter season.

How do I make sure that I get a 2200rpm fast idle during next months PV test with similar weather?

Its not really a failure as the car doesnt need to idle at 2200rpm with this weather, but in terms of the test it is a failure.

A friend of mine suggested I use an icepack around the carb. Any thoughts?

Gary

[Duke W.]

Re: 69 427/390 and 2200 RPM cold idle for PV

That seems like an abnormally high cold idle speed. What does the '69 CSM say? The JGs aren't always correct.

Duke

[Edward J.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Gary the fast idle cam has steps, Make sure when you set choke the engine fast idle cam is on the highest step. Like you said 70 degress may not be enough to set choke fast idle cam on its highest step. try the Ice trick. another thing about the 2200 RPMS is that this maybe the RPMS they looks at once the choke is fully open without touching the gas pedal after start? Don't quote me on this, the PV Manuel may spell this out for you. As Duke say sounds high I generally see 1600 to 1800 RPMS on first start.

[William C.]

Re: 69 427/390 and 2200 RPM cold idle for PV

I believe the hi rpm figure is for a warmed engine operating on the top step of the fast idle cam. If the choke is fully closed (will be even at 70 degrees) it will set the fast idle cam to the top step if properly adjusted. For a PV, The key is to depress the pedal once to set the choke, start the engine without touchimg the gas pedal after starting. The choke will slowly open as the engine warms, but will not drop off the fast idle cam top spot unless the throttle is depressed, Be patient and you will get your fast idle rpm during warmup, and once verified, you can kick it down to a more reasonable idle. Try it over a few days (takes a long time to fully cool down and get everything back to "morning normal") and see what results you get with practice. It's not as difficult as many make it out to be, as the instructions are in the least-read book in the car, the owners manual.

[Duke W.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Maybe things changed by the late sixties, but I doubt it. The fast idle is normally set with the engine fully warmed up.

In the case of my '63 340 HP the fast idle spec is 1750 "hot on car". This results in a fast idle speed of about 1500 on a cold start. Thus, there is not an actual "cold fast idle" specification, but a cold fast idle speed 2-300 revs below the hot fast idle speed spec is normal.

The reason for specifying fast idle speed with the engine fully warmed was to facilitate checking/setting it during normal servicing when the engine is usually warm. Checking fast idle speed would be part of a normal tuneup.

Be sure you and the PV judge understand this. Bring your CSM. What does your '69 CSM say about setting fast idle? Is it like my '63 that gives a fast idle speed with the engine fully warmed up?

Duke

[Dick W.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Duke, it COLD fast idle which is about 2,200 per CSM. That is where the PV specs came from

Not hard to adjust, hot Turn engine off, close choke fully manually, make sure fast idle can is on the high notch, then adjust speed. Typically you will not see full cold hi idle with FL temps if you are going to Kissimmee, but just in case it were to turn off cold (Heaven forbid) you should be prepared.

EDIT: The cold high idle is set with the engine at operating temperature. Thanks to Clup for reminding me of this

[William C.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Gary, if you look at section 6M of the service manual, it has a clear description of the process for setting fast idle.

[Gary H.]

Re: 69 427/390 and 2200 RPM cold idle for PV

I will have to check it out in the morning. I did set it with the engine hot, but never actually gave it a chance to warm up for more than 30 seconds without kicking it down.

Gary

[Terry M.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Gary,

If you think the temperature in Kissimmee will create issues for your Corvette -- get in touch with the National Team Leader -- in your case Chuck Berge. Be sure to ask him if he will be doing the PVs in Kissimmee or if he has designated someone else -- although in my experience he is usually there. Find out what he expects to see in your conditions, and how he expects your car to achieve that goal.

I was 1970-72 NTL for almost 15 years and I never saw ice used nor did I ever use it -- and I did a lot of PVs and watched a lot of others during that time. If anyone needs to go to that extreme something else is wrong, and I don't just mean the ambient temperature. We have had National Conventions in Reno at 105*F, and Collinsville Illinois at similar temperature, and while I am not sure anyone chose to go for PV at those events (Reno may have been before there were PVs) they would make January Florida temperatures look positively balmy. And yes I have been to Cypress Gardens when the plants and all of us were freezing and the space shuttle crashed. Corvettes were designed to work in all of the above conditions and should not have to be specially tuned for them. Consult the CSM, as has been suggested. As Dick said the cold fast idle specifications for the early C3 PV manuals came from those books.

[Timothy B.]

Re: 69 427/390 and 2200 RPM cold idle for PV

I think the key here is stated in post #4 where Bill explains that when the choke FULLY closes (cold start) the fast idle cam sets on the highest step if properly adjusted. Setting the fast idle to the book spec RPM is a matter of letting the engine run to full operating temperature like after a drive then adjust the fast idle screw with the fast idle cam on that high step.

After the choke pull off opens the choke blade if you touch the throttle the choke cam will always drop down to the next highest step and so on as the blade opens.

[William C.]

Re: 69 427/390 and 2200 RPM cold idle for PV

AMEN, that is the procedure and process...

[Brad S.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Gary , my 69 L36 on start up reads 1600 to 1700 and takes 2 to 3 minutes to get to 2200 . i,m in southern California and it would get to 2200 in summer heat so i don't think ambient temp is a problem

[Duke W.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Duke, it COLD fast idle which is about 2,200 per CSM. That is where the PV specs came from

Not hard to adjust, hot Turn engine off, close choke fully manually, make sure fast idle can is on the high notch, then adjust speed. Typically you will not see full cold hi idle with FL temps if you are going to Kissimmee, but just in case it were to turn off cold (Heaven forbid) you should be prepared.

EDIT: The cold high idle is set with the engine at operating temperature. Thanks to Clup for reminding me of this

So like I said the "fast idle" is set with the engine fully warmed up on a '69, right?

On a '63 AFB you bend links as required so the fast idle screw is in line with scribed line on the fast idle cam when the choke is fully closed, engine cold. Then with the engine fully warmed up you can manually move the fast idle cam to be inline with the fast idle screw, then adjust the fast idle to 1750, hot.

The procedure for the Q-jet is likely very similar.

The PV manuals should clearly state that the fast idle speed upon start-up will be a few hundred RPM less than the specified hot fast idle speed settings in the service manual, but anyone who has ever done a tune-up on a vintage Corvette with a carburetor of Rochester FI and who looked at the service manual should know this.

Duke

[Gary H.]

Re: 69 427/390 and 2200 RPM cold idle for PV

Thanks for all of your replies. I will test this out tomorrow morning. I might actually need to back the screw out a bit as I am pushing 1900 as soon as the car is started. Actually will have temps in the mid 50's which is cold for miami. Looking forward to pulling out my fathers WWII bomber jacket. Wish I could wear it more often.

Gary

[Duke W.]

Re: 69 427/390 and 2200 RPM cold idle for PV

If the hot fast idle spec is 2200 then 1900 on a cold start sounds right on the money.

Duke