VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 I cheated, but she runs fine

Hey Lee. Did you notice Chevegene's address?? According to that, he must be a tractor nut with the same preference to make as you. Probably just traveling incognito as a Chev nut!!

If and when you are at wits end with this problem, my 48 is just sitting in shed awaiting sunvisor parts and brake work, would be glad to rip carb off and send it to you to try out to ensure it is carb problem.

Jim.

You're absolutely correct Gene, if it was an original 1949, 4400 it most likely would have been a Carter W-1. I was only commenting on the Rochester because it appeared that the discussion was being steered toward the Rochester carburetors, which Lee apparently has on his engine.
Also it seems that there was some question whether there was a Rochester "C" model because of the "C" cast into his air horn. I interpreted Lee to be asking about that so maybe this picture will help illustrate where that Idea came from: http://www.pbase.com/dennygraham/image/115170647
I'll yield the floor to you now Gene, maybe you can explain why some were cast with the “RP and some “C”.

A wild guess from way out in left field might be that some were made for GM by “C” Carter when the demand exceeded the supply at the “RP” Rochester Products facility??? We do see that sort of cooperation with Ford and the Holly Webber and Carter Webber carburetors.

Denny Graham
Sandwich, IL

The "original" carburetor (the carburetor that it had on it when I got it and it was on the truck for a long time) has a brass tag. It has the number 7004475 near the attachment screw (a screw that holds the top of the carburetor (and the tag) to the bottom). Below that number and toward the edge of the tag is "C 2". That is all that is on that brass tag.

Thanks,

Lee

Tag # 7004475 is part # 7004600. This is the late design, high cover Rochester Carb. sold after 1952 and was standard equipment on 1952-1953 216 engines, cars and trucks. Is listed as the replacement for all 1932-1949 engines as well as the 1950-1953 216.
This was the best Rochester made for a 216.
This carburetor requires the proper insulator block to be installed under it as the power piston requires a sorce of engine vacuum. If not used will be in the rich power mode at all times.

Thank you, ChevGene. That explains some things to me.

When I got the truck, the vacuum line to the wipers was cracked and would even come off the manifold vacuum port, but the engine would run anyway, but gas mileage was poor. Now, with the Rochester RP GM carburetor, the engine dies if I disconnect the wiper vacuum line from the manifold.

The engine block is a 1950 216 (according to the internet serial number data) with 235 pistons, so I know it isn't the original engine (unless it was a late '49 that got a '50 engine block ... that kind of thing happened all the time with farm tractors of that era. Allis was bad about borrowing production from the next model year if the factory ran out of parts late in the previous model year. And the parts catalogs wouldn't reflect the fact that a plant manager told the assembly line guys to go get a part from the next model year's production if it existed at that time.).

The ("original") insulator block (that thing between the manifold and the carburetor) under the carburetor does not have a vacuum port for the carburetor, and I don't see where a vacuum line would connect to that carburetor. The vacuum port for the wipers comes off the manifold where the hydrovac attaches.

If the engine block is a '50 model 216 bored to 235, it is reasonable that the carburetor isn't original either.

I'll have that carburetor rebuilt after I get moved to Oklahoma.

Thanks,

Lee

The vacuum connection can not be seen from the exterior. The carburetor must be removed. Under the base of the carb. you will see a little hole. If the proper insulator block is used (for a 1950 216 and up) there will be 4 notches in the inner circle of the block. One of these notches lines upw with the hols under the base and provides vacuum to operate the power piston. If the block does not have the notches a thick asbestos gasket with the notches cut in it can be used. That gasket came with a new carburetor.

Thanks, ChevGene. That might explain the mileage problem I had been having (but don't have anymore).

I tried to get the insulator block off the manifold but wasn't able to and I didn't want to use too much force. When I put the new carburetor on, I used some gasket sealant which may be clogging the internal vacuum notch on the insulator block.

If the vacuum notch is blocked, what would the symptoms be?

Lee

Engine will run very rich will very poor gas milage.

In 1938 Chevrolet preformed the following test that was certified by AAA.
A 1938 1 1/2 ton truck rolled up 100,015.9 miles from Jan 11,1938 till Jan 19,1940. Carried a 4590 pound load with a gross weight of 9260 pounds. Averaged 15.01 MPG and 33.07 MPH.
Used 1072 Qts of oil and required $171.45 worth of mechanical work. The original tires ran 32,936 miles Every state was visited.

And they haven't been able to repeat it since???

Denny G

By the way, it is not necessary to use sealer or a gasket on the insulator block if it has the 4 notches. Just clean surfaces are necessary.

Denny,
The 1937-1939 engies were not too good in the gas milage department to begin with. Years back a few of us traveled together and we all had 1937-1939 and some times a 1940 with 4.22 axle ratios. We all would average about 15 MPH at 60-65 MPH. Now we were going faster than the truck but it was hauling a heavy load with a faster turning engine.
I would say at 40 MPH we probably would have averaged about 18 or so. My '39 gained 2 MPG when I installed the 3.73 rear end.

I kill for that kind of mileage Gene, you guys and the that 1 1/2-ton truck must have been rolling down hill all the time.
My 1950, 3604 with 61,000 actual miles on it still has its original 216 and SM420, replacement tires are the correct diameter (radials for now) and an HO52, 4.10 gear. With out any load other than my “big ol’ wife”, my over all mileage when averaged over the last 8,000 miles has only been 12.459 mpg. And this is with several meticulously rebuilt carburetors (Rochester B’s and a Carter W-1) and all of the ignition rebuilt and a complete valve job. Basic engine uses quite a bit of oil because the oil rings are shot but it doesn’t show it out the pipe or plugs and the compression still runs 130 lbs across the board. I don’t think a day goes by where I’m not touching up something on the truck so it’s not one of those that is just pumped full of gas and driven daily without opening the hood
It’s really difficult to compare any results when there are so many variables. The very first thing that one has to start out with is a solid engine with very little wear. I’m really looking forward to the results after the short block is rebuilt and broke in. Hope to get to that this winter.
Denny Graham
Sandwich, IL

One of the things that Obama got right is that increaseing the air pressure in your tires really improves gas milage, specially on radial tires.

I have been driving my '50 Styleline a good amount over the past 6 weeks. In June we went to a car show in st paul mn and drove it 600 miles in 3 days and averaged 20 mpg. The last few weeks I have a fair amount of short trips and the mileage is still in the 18 range.
With everything in top shape on Denny's truck with the exception of the short block it seems to me that with it using so much oil that it would be affecting the fuel mileage. Gasoline has a fixed amount of energy in it and if you add having to burn the excess motor oil I would think it would take more fuel.

Just a thought
Don

Gene, I used the sealant because I boogered up the surface trying to get the old insulator off the manifold. I scratched and chipped it trying to get it off. I couldn't see any seam between the manifold surface and the insulator surface and tried to gouge it off with no luck.

I need to pull the carb again to make sure the vacuum hole isn't plugged.

My gas mileage now (loaded) is over 10 mpg, but that is not stop-and-go but "county road" driving.

Lee

I pulled the carb and the internal vacuum channels are clear. It runs well now, but I'm not happy with the way I timed it and tuned the carburetor. But, the gas mileage is over 10 mpg and it doesn't miss anymore.

Lee