Farm Equipment - building a zenith carb

Print Page | Close Window

building a zenith carb

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=166347
Printed Date: 06 May 2024 at 9:18pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: building a zenith carb

Posted By: Ken in Texas
Subject: building a zenith carb
Date Posted: 04 Dec 2019 at 11:27am

for B,C,CA applications using overbore engine overhaul kits. The Carb on my bench has a small bore venture. Should I swap it out for a larger bore venture ? I have 2 larger to chose from. Like a medium and even Larger type.

I'm thinking the carb core is off a early B with a BE engine. No adjustable MAIN JET.

How hard is it to install a Adjustable Main Jet?

Replies:

Posted By: Dick L
Date Posted: 04 Dec 2019 at 3:46pm

Some larger but not a bunch with just the over bore kit. The over bore kit will not pump a much larger amount of air pumped thru the engine. You will loose lugging power if it is to large.

You just get the adjustable needle and the jet for the adjustable needle. No big deal. I have removed them from another carburetor out of my stash.

I never found an advantage when pulling with the adjustable jet once I matched the nonadjustable jet to the modifications.

Posted By: Ken in Texas
Date Posted: 04 Dec 2019 at 6:42pm

Thanks Dick L

The project I'm working on is cloning My Dad's first B. A39 hand crank. I had a early BE engine built for it 15 years ago and finally got to hear it run. The carb I used was

borrowed from my CA. That carb will not idle for nothin, so, I was hoping to build a carb from a box full of rusty ones. All that looked like early B zeniths have small venturi

. I replaced it with one with a little larger bore. I also changed the seat, needle and float with a later assembly. It idles great but blows fire and runs horrible anywhere past half throttle.

What's NEXT to get it running smooth at high RPM. I'm running out of spare parts. Need high speed jets

Posted By: PaulB
Date Posted: 05 Dec 2019 at 3:29am

As Dick says, with the proper main jet an adjustable jet isn’t needed. However with the varing fuel quality these days it can sometimes be handy. I run my pulling tractors on E85 and fuel air ratio is critical. Especially when weather conditions can vary from hot to cold and dry to humid. This can sometimes vary from one extreme to the other from one pull to the next and back again. For a trailer tart it’s just another accesary.

-------------
If it was fun to pull in LOW gear, I could have a John Deere.
If you can't make it GO... make it SHINY

Posted By: Ken in Texas
Date Posted: 05 Dec 2019 at 8:05am

Thanks Paul B

I noticed in my Jensales Parts Manual beginning on page 50 a detailed drawing of a Zenith something or another, Page 51 gives 4 part numbers for venturi of different sizes. well vent 3 different sizes . 2 or more discharge jets. 4 different fixed main jet sizes, 19,18,23 and 25.

The disks on most of my cores are unreadable so it is mostly guess work trying to figure which one of the 14 listed I'm trying to put parts in.

long and short choke shafts.

I'm to the point of being in need of 3 different zenith carbs built and ready to go, 1 each for my 53CA, my47 C, and 39 B. Actually the CA not idleing is ok

What rebuild kit to buy is another story by itself. The one kit I have pieces of is for a 61 or 161 series zenith. Any cores I have to build are off of early stock BE engines with parts broke or missing

Today I hope to get the carb I got to idle perfect to scream at high rpm.

Float adjustment ,I'm finding out is critical. All but one old style needle has the tiny wire at the top. I'm junking them for newer bigger needles with wires clipped to the knob on top

Trailer TART huh . I'm pretty sentimental about the clone i'm trying to finish

What do you think good or bad about MARVEL SCHEBLER CARBS?

Posted By: Sugarmaker
Date Posted: 05 Dec 2019 at 10:09am

Ken,

I have only done Marvel brand carbs for WD series tractors. I have a Zenith on the D17 and it has worked fine, so I have left them alone.

I think we need some pictures carbs or tractors!:)

Regards,

Chris

-------------
D17 1958 (NFE), WD45 1954 (NFE), WD 1952 (NFE), WD 1950 (WFE), Allis F-40 forklift, Allis CA, Allis D14, Ford Jubilee, Many IH Cub Cadets, 32 Ford Dump, 65 Comet.

Posted By: Dick L
Date Posted: 05 Dec 2019 at 10:28am

My C that I pulled that had the 4 inch stroke had its original carburetor body. It also had the original power jet modified to work with engine modifications. It is just cut and try until you get the results your after. I have never found a manual to cover my hair brained modifications.

Posted By: PaulB
Date Posted: 05 Dec 2019 at 2:14pm

Ken: It all depends on what you want to do. As Dick mentioned for a stock engine you don't want a big venturi. If you want all out power and don't care about fuel economy, I prefer a M-S with whatever modifications to match the motor. As I said earlier, all my pullers run on E85, so there's quite a bit to do to get the Air/fuel ratio where I want it along with EGTs under load. Due to varying conditions ie: temperature, humidity and barometric pressure I like to have an adjustable main jet.

for my large CID puller the also turns 4500RPMs I have a Holley from a 5000 Ford that I've modified to run with E85 and installed a main adjusting needle from a Holley from a 190.

For something that only needs to get on and off a trailer and to tootle around the show grounds it doesn't matter what mixes the fuel, fuel economy isn't top priority either.

For my working farm tractors (CAs) I like the later style Zeniths (model 161). These have an idle compensator for venting the fuel bowl, through a passage to the throttle shaft that puts a slight vacuum in the bowl, which helps in the mid range. These adjusted properly will give great performance and good fuel economy without sacrificing horsepower too much. The smallest venturi that will give the needed power is the best.

The early Zeniths model 61 will do fine on fuel compared to a M-S and operate satisfactory when jetted properly for the conditions.

-------------
If it was fun to pull in LOW gear, I could have a John Deere.
If you can't make it GO... make it SHINY

Posted By: Steve in NJ
Date Posted: 07 Dec 2019 at 8:08am

Just an overbore kit wouldn't effect the engines performance enough to move to a larger venturi or Carburetor in my opinion. I installed an overbore kit in my B model and then I rebuilt the stock 212845 Zenith that came on my B and its been running fine for 20 years. I tried a M/S TSX series 154 and didn't see any advantage or power increase. Seemed to run the same. A little different "dial in" on the M/S vs the Zenith, but ran just as nice... HTH

Steve@B&B

-------------
39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife