VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 Any "tricks" to make the engine run leaner?

Hi.
I have a new built engine that I am running-in on my 1934 Master.
When you are running-in an engine, I have been told that it is better to have a bit lean air-fuel mixture rather than rich mixture (to prevent fuel "washing" oil off the cylinder walls) .
As a test, I hooked up a modern digital wideband oksygen sensor to the exhaust system on my 1934 Master.
On a modern car, the "ideal" air-fuel mixture should be around 14-15 parts of air to 1 part of fuel (14-15:1) on normal driving.
On my old chevrolet, I have about 12:1 mixture, which means I am running richer than "ideal".
I have two different Carter carburetors, they are about the same when it comes to air-fuel mixture.
I tried lowering the float level on one of the carburetors, I thought that would make the engine run leaner. But on my oksygen sensor, it did not seem to make much difference (do any of you have any experience with lowering the float level)?
Maybe I could try to lower the float level even more, to see what happens.
Are there any other "tricks" you know of that will make the engine run leaner?
Or maybe i should just forget about the air-fuel mixture, and be happy as long as the engine runs and feals ok?

The "trick" for the Carter W-1 carb. is to install a leaner metering rod. The metering rod you would use would depend on the model year of the carburetor.

Fuuny that yo should mention dry cylinder walls. A member and friend just had that problem with his '34 Master. The engine would not restart, could not turn the engine over with the starter or a pry bar. First he dropped the pan to make sure no bearings had siezed-up. No problem found. The he pulled the head. No problem visable. The he sprayed the cylinder walls with WD40 and it turned over freely. The engine is not "fresh", the carb. is the later 569S W-1 and he always complained that it runs too lean, The inspections he did were per my suggestions.

My suggestion for breaking-in the engine is add some 2 cycle oil to the gas for upper cylinder lubrication.
The 1929 Chevrolet service news said a Quart of oil can be added to the gas for break-in. I would not add conventional motor oil due to all the other additives that are not designed to be burned.

I have always done this for break-in and winter storage.
Another experiment (temporary fix) is drip some oil through the carb. air horn with the engine running and note the increase in idle speed.

Thanks for your reply and advice regarding adding some 2 cycle oil. Do you see any extra smoke from the exhaust when you do this?

I will look closer into metering rods.

I thought lowering the float level would lean the mixture some too, do you have any thoughts on this?

I am not sure what you mean by "the carb. air horn". What will I find out if I do this experiment?

If you remove the air filter there is the air horn...on top of the carburetor where the air enters.
You may get a very little smoke, depending how much oil you add.

34 Master has carburetor metering rod sizes that fit the 284S Carburetor.

Standard is marked 65A46

1 step lean 66-50

2 step lean 67-52

This will help you find the correct Metering rod for your car.

The only thing is make sure you have a '34 Master carburetor. Often find it has been changed to another year or?
If the any of the numbers listed are on the metering rod it is a '34 Carb.
To get oil up on the cylinder walls don't idle engine for any length of time. Also I prefer to set idle up faster during break-in. Also drive it up to 40 MPH for short bursts.

I forgot to mention the "adjustment" of the metering rod will have an effect on the fuel/air mixture. See shop manual.

After you figure out what year carburetor you have and metering rod number you need, I may have a metering rod for you. I have a few of them.

I am in perfect agreement with everything that has been
suggested. The only thing I do that is slightly different is
that use MMO (Marvel Mystery Oil. With the engine running at
about 1200-1500 RPM I will slowly drip a couple of ounces through the carburetor. It will smoke a little, but not terrible. You can also add about 4 ounces to a tank of gas
and it will provide upper cylinder and valve stem lubrication
while creating almost no visible smoke! Either procedure will
get the job done!

Thanks.
I might need some help identifying the Carter carburetor I have in my car now. Is there a "guide" on internet that can help with this?
Here is a picture (let me know if you can not see the pic) http://i939.photobucket.com/albums/ad235/mikjel/IMG_5944.jpg
To me, it looks like the original carb that was on 1934 Master cars, except it has 3 bolts (instead of 2) attaching the air horn to the carb. body.
The metering rod which is in now is: 75-176
I do not know which leaner metering rod will be correct for this carb then?

Another "trick" to make the mixture leaner, could maybe be to bend the long throttle conector rod a bit, then the metering rod would be lowered a bit (same effect as putting in a thicker metering rod - letting less fuel through?). I do not know if it is worth a try..

According to my book a 75-176 metering rod goes in a 1935 or 1936 carb. 319S or 334S. 319s is 1935 Late models and early 1936 is 334S. Looks like you should see this number on the side of the carb. or look for Chevrolet carburetor No. 837894 on 319S with a casting number on the face of flange 65 or 334S 838013 and casting no. 65 face of flange. both fit master and deluxe. If this is the case then the 1 size lean would be 75-181 and 2 size lean would be 75-182 on both. I do show a pined in note 75-144 and 75-171. Proving which one you have is a must. 75-176 is a standard metering rod.

The numbers on the side of the carb are:
1261756 (or 8 instead of last 6).
1831056 (or 8 instead of last 6)
1588614
1858615
1881986
1944531
1961747

The carburetor body pictured is a '36 (3 air horn screws & 2 float bowl screws). Adjusting the coordinating rod to lower the metering rod will give a leaner mixture. Lowering the float will also but generally less.

At one time I was a Marvel Mystery fan. Then I saw the contents and changed my mind. It is basically a form of keresene with coloring and a mint oder added. Thats when I changed to 2 cycle oil. It is a full body oil , less needs to be used, and designed to be burnt in the combustion chamber.
MMO is still a good solvent for loosening carbon and disolving sludge and thinning oil for winter use.

A couple of thoughts:

First, here is a link to my website that should help you identify your W-1:

http://www.thecarburetorshop.com/CarterChevroletW1.htm

Next, I don't disagree with any of the posts in this thread about how to lean out the carburetor.

Finally, my question would be WHY would you want to lean out the carburetor on a fresh engine??? I will confess to never have broken in a 1934 Chevrolet engine; HOWEVER, since I started working on engines (cars, trucks, tractors, etc.) in the early 1950's I have been taught to ALWAYS make the mixture RICHER when breaking in a fresh engine! The reason.....heat. It takes new components some time working together to loosen things up a bit, and in the meantime, heat from friction can be an issue, even to the point of seizing an engine. Washing the oil from the rings is possible, but probably only if the engine is so ridiculously rich it won't start! Then you would have unburned fuel sitting on the piston, that would seep down on the rings.

Would really like to know the source of trying to make a fresh engine run leaner.

Jon.

Thanks for your input Jon.
I had an engine rebuilt for another car a few years ago by an experienced engine builder (this was a modern, fuel injected engine). He told me it was a good thing to run a little lean when I was running in the engine, a richer mixture could "wash" the oil off the cylinder walls.
I thought he knew what he was talking about, but he might have been very wrong.
I do not know, I have no more knowledge or experience with this my self.

I would suspect engines from that long ago were inifficent and would be difficult to get down to todays fuel/air ratio.
A little 2 cycle oil in the gas, avoiding long periods of idle and running a "thin" oil and taking the car out and driving at various speeds up to 50 MPH will all help . I used to take the car out and drive it 10 miles each day (or time) til it got 2 or 300 miles on the engine so as to break it in under controlled conditions.
Just running the engine and not driving the car on the road will not break-in the engine properly.