The Big Nut Carb


June 1995

First, a little background about myself. My name is Greg Stephen and I am a John Deere dealer in Franktown, Colorado. I have been involved in the parts business over 16 years. I started collecting about 14 years ago and have been at it ever since. Our dealership has been around since the 1930s and we never, ever throw anything away! I thought it might be interesting to write a column about some of the NOS (new old stock) parts that I have gathered and explain their application and usage.

The subject of carburetion and fuel systems on older tractors and vehicles is very interesting. The idea of utilizing a mechanical invention to replace horse-drawn farming was considered untested and unreliable. Most farmers had never owned or maintained a tractor before. Carburetion and fuel systems were in a state of constant change and improvement as new designs were developed and tested. Changes came about as company engineers gained experience and knowledge from actual field experience and owner feedback. At one point, it seemed as if everybody in the business had an idea for a carburetor and no two were the same. Many carburetors were produced and enjoyed tremendous popularity and acceptance for a short period of time, only to disappear as better designs were introduced. Gone today are names that formerly dominated and controlled the industry. Once familiar names such as Ensign, Bennett, Kingston, Breeze, Browne, Stromberg, Krice and Rayfield are all examples of carburetors that have either survived in limited specialty markets or disappeared entirely.

Some brands managed to continue in the fuel system industry. Zenith, Holley, Carter and others have all continued manufacturing carburetors as independent companies or divisions of larger corporations.

One such company is Marvel­Schebler. Although purchased by a larger corporation, Marvel-Schebler supplied many carburetors for John Deere equipment and is arguably the brand of carburetor most familiar to John Deere collectors. Early Deere tractor models utilized differing carburetor brands. The 1923-1927 model “D” used a large Schebler brass carb. This carb is known as the “Big Bowl” brass Schebler carb or AD103R brass “D” carb. The same basic style of carb was used on the Waterloo Boy and various Hart-Parr tractors. The 1928-1935 model “GP” used several styles of Ensign carburetors. These are known today as “Brass GP” carburetors. Later “Ds” and “GPs” began using a carburetor that more closely resembled the carb that was widely used on the “A’s,” “Bs,” “Gs,” “Hs” and “Ds.” The earliest versions of these Schebler carburetors had brass main bodies and cast iron bowls. Early “A’s” used a DLTX-8 brass-body carb, mid-production “Ds” used a DLTX-6 brass-body carb, early “AR”/”AOs” used a DLTX-9 brass-body carb, and later “GPs” used a DLTX-5 brass-body carb. The majority of the John Deere two cylinders used cast iron carburetors, of single and dual barrel design.

Of this style of Schebler carburetor, the one that is the best known is the one pictured in this article. Shown in the left side of the picture is John Deere part number AR10041. This is the main body casting for a Marvel­Schebler DLTX51 carburetor. This carburetor was used on the John Deere “G,” serial number 13000-up. All “Gs” prior to this serial number used a Marvel­Schebler DL TX24 carburetor. The DLTX51 carburetor is more popularly known as the “Big-Nut” carb. The “Big-Nut” carb has a very large brass retaining nut on the bottom of the bowl and is infamous in tractor pulling circles due to the extra horsepower that can be gained by bolting this carb onto an “A,” “G” or “D.” I installed a new “Big-Nut” carb on a styled “D.” I then dynoed the “D” after the installation and realized a five horsepower gain! This is particularly impressive when you realize that this was accomplished at an altitude of over 6,000 feet!

The carb on the right side of the picture is an NOS “Big-Nut” carburetor. These carburetors are extremely difficult to find used and my supply of NOS carbs is running low. I hope you enjoyed seeing what a new “Big­Nut” carb looks like. I’ll look through my parts and see what I can find for next time! Bye!