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Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: PequotMonza64 ()
Date: June 14, 2022 11:45PM

When I got this car, it idled quite high in neutral, even when the engine was warmed up, and then much slower and seemed about right in drive. I know the spec is to set the idle rpm with the Powerglide in drive.

So, why does it need to idle so fast when in neutral? Is the Powerglide such a load even when you're not moving?

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: RobertC ()
Date: June 15, 2022 12:22AM

Think you are "over thinking" the issue.

The most important "spec" on a PG equipped Corvair is that it does not stall when you put it in Drive.

The idle speed can be affected by the condition of the engine; condition / setup of the carbs; ignition timing.

Technically, it should not creep when in Drive and your foot is not on the brake.

This may be harder to achieve - depending on factors mentioned above.

Since you do not state idle rpms in neutral and drive, we really have no clue?

Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: PequotMonza64 ()
Date: June 15, 2022 01:28AM

I'm not overthinking anything. It's a simple question related to why the factory specs and procedures are what they are.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: JimBrandberg ()
Date: June 15, 2022 05:59AM

I get a good idle in Neutral and if it dies when shifted into gear look for what's wrong.
If it's idling high in Neutral it may not even be running on the idle circuit. When properly idling you should be able to pull the vacuum advance hose at the distributor and see no change in the vacuum advance arm.

Jim Brandberg
Isanti, MN
CorvairRepair.com



Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: Paulsgt ()
Date: June 15, 2022 06:33AM

I had to set the idle speed in neutral up a bit on the engine in my convertible because the engine has some blow-by and would act like it wanted to die in drive with my foot on the brake. I suspect that if everything were factory-perfect, it would be fairly easy to achieve a low idle speed (set to specs) with PG in drive.

Enjoy the Corvair!

Paul Sergeant
CORSA Central Division Director / CORSA Treasurer
Lee's Summit, MO
CORSA since 1975
Member – HACOA, Corvair Minnesota, CORSA, Little Indians, POCI


Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: corventure Dave ()
Date: June 15, 2022 06:53AM

Also check for vacuum leaks. They could be anywhere.. Carb base gaskets, bad choke pull off's on carbs, modulator and vac hose to modular, Vac balance tube hoses connected to it. Vacuum advance hose, warn throttle shafts in the carbs and other.

A slight vacuum leak will make for a lean mixture and not allow the engine "with Powerglide" to idle in drive at factory spec.

Corventure Dave

Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: 63ConDan ()
Date: June 15, 2022 08:23AM

corventure Dave Wrote:
-------------------------------------------------------
> Also check for vacuum leaks. They could be anywhere.. Carb base gaskets, bad choke pull off's on carbs, modulator and vac hose to modular, Vac balance tube hoses connected to it. Vacuum advance hose, warn throttle shafts in the carbs and other.
>
> A slight vacuum leak will make for a lean mixture and not allow the engine "with Powerglide" to idle in drive at factory spec.
>
> Corventure Dave


Pequot, as a sitter for so long this is a likly cause. Get her back to together and maybe with the carb work you did, your leak will be fixed and she will purr.

As a side note. I spent some time at place called Brezy Point about 5 miles east of Pequot Lakes MN. And my Uncle who owned this lake place at brezy Was a pilot for NWA out of MSP. he has long since passed but Id bet he knew the orginal owner of your car. I'll inquire to his kids, my cousins, when I run into them.

Best to you on your repair.

Dan Central MN
1968 Convert

Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: PequotMonza64 ()
Date: June 15, 2022 09:43AM

Thanks, Dave and Dan.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: Frank DuVal ()
Date: June 15, 2022 09:56AM

Have you found a tachometer to see what is going on?

The real question is not how high the neutral speed is, but how hard does the transmission engage when the lever is dropped to Drive?

Frank DuVal

Fredericksburg, VA

Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: PequotMonza64 ()
Date: June 15, 2022 10:10AM

Still reassembling the engine, Frank. I understand about the stalling issue. Can't tell you what the revs were when I picked up the car and drove it home, but I would guess at least 1500 rpm, not racing but noticeably high. When in drive, the revs dropped to what sounded like a normal speed.

I was really just asking about the factory spec which tells you to set the idle speed with the car in drive rather than in neutral. Never saw that before.

When I get it back together, we can explore this more thoroughly. The carbs and everything else seem to be in good shape (assuming the carb shafts aren't leaky). I think I can just set the idle as low as possible so that when you engage drive there's no stalling.As it was during my first drives, I think it was a little high.

Thanks for the input.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: wittsend ()
Date: June 15, 2022 11:16AM

Ignition/Timing:
Getting the idle and timing set can be like 'a dog chasing its tail.' On the ignition side the timing can seem correct but you may be into centrifugal advance and/or vacuum advance in neutral. Putting the transmission into Drive drops the RPM's causing either ignition advance method to decrease the timing and potentially causing a stall.

The first thing you should do is disconnect the vacuum advance hose and plug it. If the idle speed changes upon disconnect and/or you can feel vacuum at the hose the carburetors are likely set at too high at idle. With the hose disconnected and plugged set the ignition timing. This may causes the RPM's to increase (or decrease). Like I said, 'a dog chasing its tail' and the idle speed needs to be adjusted. The goal is to get the centrifugal timing set at (or slightly above, as needed) the stated RPM. Personally I would leave the vacuum advance disconnected and plug until after the carburetors are adjusted for idle.


Carburetor air balance, idle speed and mixture optimization:
The carburetors may be out of sync and/or the mixture not optimized. It might be at idle one half of the unloaded engine is doing the bulk of the work. Then, putting the load of the transmission on the engine is causing it to stall.

More of the 'dog chasing its tail' is to get the air portion of carbs synced (balanced) at idle. You need a tool like a Unisync so as to ensure that each carburetor is drawing in equal amounts of air at idle. This is done at the adjustment for carburetor throttle blade stop. This adjusting process can increase or decrease the RPM's as the carburetors are brought into sync. Thus the person adjusting is often going back and forth achieving the proper RPMs AND making sure that is achieved with each carburetor drawing air equally.

And yet more of the 'dog chasing its tail...' the fuel side of the idle (mixture) needs to be adjusted so as each carburetor at idle is providing the ideal amount of fuel. This "ideal" will be noticeable where the engine runs the smoothest. Again, this can raise or lower the RPMs. Thus after adjusting the mixture the person adjusting has to readjust the throttle stops both achieving the proper RPMs AND keeping the carburetors balanced.

In summary:
The vacuum advance is disconnected so as not to induce added timing when setting the centrifugal advance. The centrifugal advance is set at the stated idle RPM. Once set the timing should not be altered. And as long as carburetor adjustments keep to the stated RPM the timing should not change.

The carburetors first need to be balanced in that they are equally drawing a similar amount of air. And..., that the amount of air maintains the stated idle RPMs. Likewise the amount of fuel (mixture) at idle needs to be optimized (smooth running). And again the RPM's may increase or decrease with the mixture adjustment. In as much as the mixture adjustment is for smooth running (don't change once set) the throttle blade adjustment is for re-setting the RPM's - once the mixture is optimized. Re-connect the vacuum advance when completed. There should be no change in the engine RPM upon doing so.

In Sub Summary:
Balance the air the carbs are using. Adjust the mixture for smoothest running, re-adjust the air adjustment to achieve the proper RPMs while at the same time keeping the carburetors balanced.

This may seem confounding and confusing. With experience it takes about 5-10 minutes to achieve. Knowing WHAT is being adjusted and WHY is extremely helpful to mastering the process. There are a number of ways to achieve an idle at a specific RPM but there is only one right way with proper timing, proper air balance and mixture optimization. Assuming there are no vacuum leaks it is my assumption that something is askew in the adjustments mentioned above.

------------------------------------------------------------------------------

***'61 Lakewood, a "Freebie" in hibernation for 27 years - In the process of applying CPR.***

Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: junkman ()
Date: June 15, 2022 12:40PM

Factory specifications are based on a new engine, not one with 50 or 60 thousand miles on it. With age, all parts of the engine move out of specifications. In most carburetors, the throttle shafts are worn enough to leak with those miles on them. You can rebuild them with a new kit, but unless you have the experience and the tools to drill out the throttle shaft holes and line bore and install new bushings, they are always going to leak. In fact, they probably were not that tight-fitting when they were new. A good carburetor rebuilder will drill, line bore, and custom fit the replacement throttle shaft so it will be better than a new one. These cars were never designed to go 100,000 miles, and back in the 1960's most people would trade their cars for a new one once they got up to 50 or 60 thousand miles. At 100,000 miles, it was considered a winter beater to keep your good car in the garage till all the snow and salt were gone from the roads.

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Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: vairmech ()
Date: June 15, 2022 05:53PM

Hmmm, Any PG engine that is in good condition should be able to idle at 550 rpm and that should equate to about 700 rpm in neutral. Any more rpm and when you shut the engine off after running down the road you will get run-on.
On most engines I see I just set the idle at 700 and when you put it in gear the idle is magically 550 rpm! There are a few that are up by about 50 rpm but it still works.

As far as how hard it hit in low when you put it in gear means nothing really, when you have a bad spring in the low gear actuator I don't care what rpm, it will hit hard when you put it in gear.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: alphasud ()
Date: June 15, 2022 06:27PM

I personally ran into this issue with a PG car. The mistake I was making was to try and achieve what I thought was the correct idle in drive. However the more idle speed I added the more I got into that gray area when vacuum and centrifugal advance was starting to come in or did not fully return after releasing the throttle. I told my friend Craig Nicol about my frustrations and how it seemed the torque converter was dragging the engine down. He helped me see the Forrest through the trees so to speak.
I was approaching this problem backwards. Bottom line is get everything in order as others described and then start with a low idle in neutral so you don’t work against converter stall. If you find your idle speed in drive is causing stalling reduce the neutral idle speed until you have minimized the RpM drop when shifting into gear.
I ran into a similar situation with a V8 that someone installed a performance cam. With the low vacuum the idle had to be set to make a stable idle but the car stalled when placed into gear. A converter with a higher stall speed would have helped this situation.

David North Idaho
1965 Corsa Turbo converted to 140
1971 Super Beetle with 2.5L Subaru engine
1988 Citroen CX 25 GTI Turbo

Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: PequotMonza64 ()
Date: June 15, 2022 07:34PM

Very, very helpful, Ken. And this car did run on a bit after it was shut off.

Also, Alphasud. Very helpful.

I'll be getting to this in the next few days (I hope) and I'll remember these comments and some others as well.

Tonight, I cleaned (really cleaned) the generator and painted it with Underhood Black which is what I had on hand. Should look good. I went fancy and painted the magnesium fan lightly with flat silver high temp exhaust paint. Too much black in here.


vairmech Wrote:
-------------------------------------------------------
> Hmmm, Any PG engine that is in good condition should be able to idle at 550 rpm and that should equate to about 700 rpm in neutral. Any more rpm and when you shut the engine off after running down the road you will get run-on.
> On most engines I see I just set the idle at 700 and when you put it in gear the idle is magically 550 rpm! There are a few that are up by about 50 rpm but it still works.
>
> As far as how hard it hit in low when you put it in gear means nothing really, when you have a bad spring in the low gear actuator I don't care what rpm, it will hit hard when you put it in gear.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: PequotMonza64 ()
Date: June 15, 2022 07:35PM

Thanks, Alphasud. Worthwhile advice.

Glen in Ohio
1964 Monza Sedan Powerglide 110 hp
Low mileage survivor, stock as delivered
Records back to 1967 in Pequot Lakes, Minnesota
Original dealer Mike Turk's in East Liverpool, Ohio
Located in Cleveland, Ohio area


Re: Why is Powerglide idle speed set in Drive and then so high in Neutral?
Posted by: MattNall ()
Date: June 15, 2022 08:25PM

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