What jets should I be using?

T

tweetiebirdcenter

Junior Member
I have a 1936 engine in my car. I removed the carb to clean it and found that it has .051 jets in the carb. After I installed the carb and adjusted it, it was loading up so I cleaned and gapped the spark plugs. The car idles roughly but is very responsive to accelerate. The tailpipe has black soot so I know it is running rich. My question to you is this; What jets should I use on my 94 carb if I am 5280 feet of altitude??:mad:
 
Service bulletins cover that...I think 2 numbers down at 5,000 feet, also try 3 down because your 51's are sort of the high end of the stock sea level range.
 
If you are at 5280, I am using .54's. I live at 8300 ft. but most of the shows and cruses are in Denver, so it is rich up here but good to go in Denver.
 
You cannot read your tail pipe colour or spark plug colour as easily as we used to with the old leaded petrol. I think it tends to look a bit sooty now, when the mix is about right.
The 41 to 47 parts book says for both engine sizes (3 1/16" and 3 3/16" bore) that the main jets at .050, is normal up to 5,000 feet and .048 from 5,000 feet to 10,000 feet.
This may vary from engine to engine and your CR might be lower in your earlier engine, but it is a reasonable indication that you are in the ball park.
If you change to smaller jets, you might find she runs hotter?
I have to say that I have no real experience with these motors. I am a mechanic, but a late starter with these motors.There are plenty of guys here that know more than me.
 
I would definately go to the 48's then run a test as follows: bring the engine up to temp then remove the air cleaner and just bring your hand over the carb from the side and listen to the revs. If the engine speeds up it's too lean, go up one. This is an old fashon way of running a manual AF meter (ALL Fingers)
 
Merc Cruzer said:
If you are at 5280, I am using .54's. I live at 8300 ft. but most of the shows and cruses are in Denver, so it is rich up here but good to go in Denver.
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I'm thinking this must be a typo. Your numbers are going in the wrong direction! 50-51 for sea level, smaller at higher elevations.
 
Sorry for the confusion, the difference is the carburetor and the year of the car. Mine is a 53' Merc with a Holly 1901 Teapot. Calls for .56 at sea level and .54 for 5000 ft. I have to admit I am surprised at the difference between the two engines and carbs. I am still learning each day.
 
Bluebell said:
You cannot read your tail pipe colour or spark plug colour as easily as we used to with the old leaded petrol. I think it tends to look a bit sooty now, when the mix is about right.
The 41 to 47 parts book says for both engine sizes (3 1/16" and 3 3/16" bore) that the main jets at .050, is normal up to 5,000 feet and .048 from 5,000 feet to 10,000 feet.
This may vary from engine to engine and your CR might be lower in your earlier engine, but it is a reasonable indication that you are in the ball park.
If you change to smaller jets, you might find she runs hotter?
I have to say that I have no real experience with these motors. I am a mechanic, but a late starter with these motors.There are plenty of guys here that know more than me.
Click to expand...

The self deprecation doesn't fool me.
 
Thanks to everyone's for their suggestions. I changed to .048 today and what a change for the better. I think this car came with a Stromberg 97 instead of a 94 at least I have heard that from other people. Thanx again!
 
Yes, 1936 flathead V8's originally came with Stromberg 97's. I was going to mention also to make sure the power valve in you're 94 isn't leaking from the diaphragm or gasket seal, but if the jet change fixed it...., never mind about the power valve.

Sal
 
Your 1936 Ford (engine) originally was fitted with a Stromberg 97 carb as standard. 94 type came later during 1938. Regards, Kevin.
 
Merc Cruzer said:
Sorry for the confusion, the difference is the carburetor and the year of the car. Mine is a 53' Merc with a Holly 1901 Teapot. Calls for .56 at sea level and .54 for 5000 ft. I have to admit I am surprised at the difference between the two engines and carbs. I am still learning each day.
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Got it. And I only know 94's! Thanks!
 
"I have to admit I am surprised at the difference between the two engines and carbs. I am still learning each day."

Size of jet needed is going to be largely a product of available pressure drop in the venturi pulling the gas through. This is partly a matter of the efficiency of the design, partly diameter of carb bores.
Within one carb family, bigger versions will need bigger jets; 1936 Fords make a good example for this! They came with 1.03" Model 48's early in the year needing .048 jets, .97" 97 carbs with .045 jets late in the year, AND the .81 carb with .035 jets was available over the counter as an econo carb for city delivery vehicles! All on the base 221 engine. June 1936 bulletin covers the .81 carb, adapted from the Europe only that year 60 engine!
 
Hello my Ford Barn Brothers. Main Jets in my "Ford" 94 carb has puzzled me. Finally scored some different sizes at RPM Performance 5 different pairs for like $12 on Ebay.
Pulled out 50's, and I believe they were original in my 47 Flatty. Tried 54's first, since I'm in So. CA. near sea level. Always thought (since Oct last year) since I owned this car - that it was doggy. Ran OK when RPMs were up, but slow on the get go from stop and going up hills. Must mention, I installed a 3" riser - kinda dumb at first, since it's a stock motor.
Then I installed 56's, ran even better than the 54's. Biggest I bought was 58's, so put them in. And, it even got a little better on the acceleration and torque up the steep hills. Now at least I can go through the gears with some respectful pull. I'm old now, so it really didn't bother me much. Dig?
Now I'm there and it's time to continue to enjoy driving this very cool car. Might get more out of it if I go back to a stock riser, but that nice cool gas doesn't hurt on hot days. Stopped my gas expansion issue and leaks no more, even on the hottest days.

In closing, I just want to thank you all for the great advice this last year. Enjoy!
 
Well barners I'm not sure if it's the fuel difference or the location over here but my stock 36 with a new strom 97 is now down to 41 jets and runs like a dream.
With the original 45 jets A/F was in the high 12's. 43 jets was in the low 13's.
Not sure what the readings are with 41 jets. I'll just have to borrow Lawrie's
A/F meter again.
Kpar
 
mikewitt said:
Hello my Ford Barn Brothers. Main Jets in my "Ford" 94 carb has puzzled me. Finally scored some different sizes at RPM Performance 5 different pairs for like $12 on Ebay.
Pulled out 50's, and I believe they were original in my 47 Flatty. Tried 54's first, since I'm in So. CA. near sea level. Always thought (since Oct last year) since I owned this car - that it was doggy. Ran OK when RPMs were up, but slow on the get go from stop and going up hills. Must mention, I installed a 3" riser - kinda dumb at first, since it's a stock motor.
Then I installed 56's, ran even better than the 54's. Biggest I bought was 58's, so put them in. And, it even got a little better on the acceleration and torque up the steep hills. Now at least I can go through the gears with some respectful pull. I'm old now, so it really didn't bother me much. Dig?
Now I'm there and it's time to continue to enjoy driving this very cool car. Might get more out of it if I go back to a stock riser, but that nice cool gas doesn't hurt on hot days. Stopped my gas expansion issue and leaks no more, even on the hottest days.

In closing, I just want to thank you all for the great advice this last year. Enjoy!
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I have a feeling your power valve isn't working. You are running really fat jets, likely covering up a lack of flow from the PV when accelerating.
 
Re Mikewitt's car, I'd agree, there is probably an issue elsewhere, (power valve circuit or the accelerator pump). A 94 on a stock engine should not require 58s regardless of location.

It may also be worth mentioning that when talking jet sizes make sure you are clear whether it is a 94 or a 97 you are referring to. The jet sizes on a 97 are typically smaller than those on a 94. A novice can easily get misled.

The last comment is not aimed at anyone here, just a general comment.

Mart.
 
Ol' Ron said:
I would definately go to the 48's then run a test as follows: bring the engine up to temp then remove the air cleaner and just bring your hand over the carb from the side and listen to the revs. If the engine speeds up it's too lean, go up one. This is an old fashon way of running a manual AF meter (ALL Fingers)
Click to expand...

Ron--that "trick" works on modern mass airflow sensors too---finger in the center reduces airflow over thesensor---lean, finger at the edge increases airflow over the sensor--rich ---a mouse taught me this by making a nest at the edge of a sensor
 
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