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1951 Studebaker Smooth Idle in P and N Rough Idle in D

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New User

May 12, 2023, 4:07 PM

Post #1 of 7 (248 views)
1951 Studebaker Smooth Idle in P and N Rough Idle in D Sign In


Looking forward to seeing what everyone knows on this forum! I have the following:

Make: Studebaker
Model: Commander Land Cruiser
Year: 1951
Engine: 232 V8
Mileage: 11,800 unconfirmed original

With the following carburetor:

Manufacturer: Stromberg
Model: Aerotype 2-barrel
Model Number: AAUVB26
Choke: Integral Automatic

I rebuilt the carburetor in January 2023 with a NOS rebuild kit, soaked all parts and compressed air dried as per the shop manual. I have the adjustments, or so I believe, matching the ones outlined in the shop manual. The idle in park runs at 600 RPM (manual calls for 550 RPM - 600 RPM). Dwell range from manual is 22 degrees – 29 degrees. Dwell meter reads 24 degrees.

All of that said, the problem is this

Idles smooth and on target with specs in the manual when the car is in Park and Neutral. The moment I think about putting the car in Drive, the car idles rough. The RPM tends to sink down to around 450 RPM when the car is in drive. I am led to believe there is an issue with the power circuit in the carburetor but did not want to prematurely take the carburetor back apart before consulting. Not sure if one of the check balls is sticking, debris accumulation after it was installed, or other. Mechanical fuel pump seems to be working and was rebuilt two months ago. I wouldn't think it would be a fuel issue if I am able to maintain idle, unless that is bad logic.

Thank you,


(This post was edited by Hammer Time on May 12, 2023, 4:47 PM)

Hammer Time
Ultimate Carjunky / Moderator
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May 12, 2023, 4:47 PM

Post #2 of 7 (237 views)
Re: 1951 Studebaker Smooth Idle in P and N Rough Idle in D Sign In

Yes, I think that is bad logic.

It's always possible you don't have the mixture screws adjusted properly or you didn't use a strong enough chemical when the carb was rebuilt. The power circuit has nothing to do with idle. It's an acceleration component. Being in drive adds load to the engine so this is not unusual.

I would be more concerned with the compression readings on all cylinders. What are they?

Also if this has a vacuum power booster make sure it's not leaking.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

(This post was edited by Hammer Time on May 12, 2023, 4:48 PM)

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Sidom profile image

May 12, 2023, 5:24 PM

Post #3 of 7 (224 views)
Re: 1951 Studebaker Smooth Idle in P and N Rough Idle in D Sign In

Your RPM specs are too low. That 600 is for in drive. Any engine that doesn't have some type of idle compensation will drop in rpm when going into drive due to the excess load.
Your dwell angle is a bit low for new points, its better to get it closer to 30 degrees
What is the timing set at?

As far as the carb adj goes, it would easier, faster and better if you check out some you tube vids. what the old timer would beat into you when doing tune ups.
That's the order you do it in because one will affect the other

(This post was edited by Sidom on May 12, 2023, 6:43 PM)

Tom Greenleaf
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May 15, 2023, 5:49 AM

Post #4 of 7 (156 views)
Re: 1951 Studebaker Smooth Idle in P and N Rough Idle in D Sign In

You haven't been back? IF solved please say so.

Some ideas if not the "vintage" more than any specific one.
I looked up some stuff still questions and opinions on this era>

Dwell or the meter would be old or a new contraption vs the listing for point gap is and should be enough.

* Things folks changed on 6V engines if done is it 8V battery with regular tweaked to do that.
* Has it be made 12V. Either is it perhaps POS ground?
** Why? IDK a meter (may be) that's going to help with that if so that I would trust.
Insert: I own a 12V POS ground, runs new - other issues.

* Distributors may have oil cups as other motors. Manual would tell you don't over do it or don't.

* I'll take carb as done distributor can cause this so things to know via ohms that pass thru before ever installed see that they are aligned for full contact.

* Easy when point's bumper is low on cam push it towards points see if it drops a feeler gauge! That's shaft wobble say if it does a lot.

* Points with use raise dwell which is smaller gap as the bumper that rides cam wears - all did, still do.

* Slow that with small smear of high temp (now silcone avail) grease i or if a felt thing upside of rotation the stay put many more hours don't need new points if ohms are right, 100%, full contact - was done out of car can do in car.

* Last thought is fuel (any) now isn't this vintage even so floats if brass and soldered have a weight listed some have some fuel inside you don't notice or just weigh too much - mixture all off would be rich.

Many you could hold float and measure where it sits, top off carb redone would require checking new needle valve now isn't worn an old wrong adjustment would make if off now - perhaps a lot.

Can do engines however they were used for powering thing many not cars at all.

Good luck try to use known fuels types of alcohol will ruin the gaskets of the vintage IDK many place sell equipment fuel, rated would only use that cost no factor last seen close to double (low volume sales high cost to store it) maybe more?

New User

May 15, 2023, 7:23 AM

Post #5 of 7 (144 views)
Re: 1951 Studebaker Smooth Idle in P and N Rough Idle in D Sign In

Thank you for the reply. I have not been able to get back to the car, but I will look at the compression readings for all cylinders and see where we are at. There is no vacuum booster installed. Not very familiar with carburetors but am compelled to learn before running over to the local shop. Original intention was to rebuild and learn along the way.

New User

May 15, 2023, 7:34 AM

Post #6 of 7 (140 views)
Re: 1951 Studebaker Smooth Idle in P and N Rough Idle in D Sign In

Thank you for the reply. Not being smart here but in the manual it says to set at 550-600 while adjusting the idle mixture screws in park. Though the manual doesn't actually say that the car is in "park" I assumed it would be in park if the idle mixture screws were being adjusted.

Again, not trying to be smart as I am learning how how to adjust a carburetor, so all the information is great to have. Just need to understand idle in park versus idle in drive with foot on the brake (not sure it is called idle in drive). I can look at adjusting the RPM in drive higher to see if that helps. Appreciate the response.

Tom Greenleaf
Ultimate Carjunky / Moderator
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May 15, 2023, 8:20 AM

Post #7 of 7 (132 views)
Re: 1951 Studebaker Smooth Idle in P and N Rough Idle in D Sign In

There's LOAD on the engine out of P or N. Some but little otherwise.
Early for auto trans at all search out rear pumps see if it applies - can start those without a batter? Goofy differences.

Alternators not in use yet so regulating voltage could be a regular you could also adjust! Keep those in line, not too low or high watch it work live voltage and over charging batteries an issue then, still is.

IMO OK and preferred to raise idle it keeps oil pressure higher should be one screw with a spring so it stays there.

Carb adjustments? Hope that's done i all apart clean well, watch the ports are clear and set float the rest is mostly passive.

Last I love old stuff just not being old :-) Don't forget how many things have grease and oil spots (not engine) if it moved it had a way to lube it.

Your call how clean you want things oiling stuff makes a mess, not doing so wears things out.

Laugh - you'll have a collection of tiny oilers should still be grease fitting used today some things even on leaf springs - if so, do it!

Enough, just use it some look at your directions owner's manuals had specs in them hope you have it the float level is what alters mixture the rest is set once!

Count turn out from bottom if out for cleaning after lots of use CAN'T ON EVEN LATE CARB THINGS - folks thought that would give power back - it didn't, Tom

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