Another Question. This one Replacement Carburetor

[AVS619]

I am still learning to adjust the Schebler Model L on the 1910 IHC -30. The tour is two weeks from today. It has been recommended to me to get a modern Zenith universal carburetor either to replace the Schebler or as a back-up. So, I talked with John at Auto Test Systems and Mike Framer at Zenith but I am left a bit confused. It appears that one of two models should work, a 14998 267 -10 or a model 14996 267 - X9. Both will fit my bolt hole pattern although both have a throttle bore a bit less than the bore of the intake manifold. The 144998 is about 1/8th smaller and the the other about 1/4 smaller. What I do not understand is the venturi sizes. the 14998 has a 24mm size and the 14996 is 21 mm. Both they say are bigger than what they say would be best for a four cylinder 4 in bore and 4 inch stroke running at about 1500 to 1800 RPM max(?) which would be about 18mm. OK, that left me in the dark. Can anyone shed light on what they are talking about and can anyone recommend which model to order, the 14998  267-10 or the 14996 267-X9? I really want to tour with this car in the next few weeks and many time in the future. Thank you in advance.

[Guest bugged]

Hello.

I would suggest you read over this information.  It is pretty straight forward.  If the people at Zenith used the Bore - Stroke - RPM etc. info you gave them this is probably how they arrived at their recommendation.  I use Zenith universal carburetors on my 3 'teen cars and they are great.  I bought my carburetors from Automotive Test Systems.  I have talked to ATS and Mike Framer at Zenith.  They are good people.  I hope this helps you.  If you still have questions, I'll try to help.

 

  Carburetor & Venturi Sizes

Size of carburetor: The carburetor capacity required depends upon the piston displacement (piston area X stroke X number of cylinders) and upon the service for which the engine is to be used. The capacity of the carburetor is gauged by the throat diameter of the large venturi.
To find the size carburetor needed for a given engine, find the cubic inches piston displacement from tables on page 1047; table below will then show the carburetor size and venturi size recommended. (For bore and stroke of different size engines see pages 1058, 966, 996; for make and size of carburetor see pages 1055, 966, 996, of Dyke's Auto Encyclopedia.)
Example: Given a four-cylinder engine of 33/t" bore, 5" stroke, installed in a pleasure car. The piston displacement, according to table on page 1047, is 221 cubic inches, and from the table below, we find this to require a 12" venturi, in a 1%" size type "0" or "OS" carburetor.
If the engine were used on a truck, it would probably be better to use a 33" venturi, in a type "M" or "MB" carburetor.
The tables on this page are computed in the case of the Model "O" carburetor for maximum torque and volumetric efficiency at 1,700 r.p.m. and for Models "M" and "MB" carburetors at 1,200 r.p.m.
For faster and slower speeds, a corresponding addition or reduction should be made in piston displacement value before selecting the venturi size.
Larger venturi sizes may be used on engines which have proper application of exhaust heat on the intake manifold.
For fewer than four cylinders on one carburetor, use the same venturi size as required for four cylinders of the same bore and stroke.

 

Edited September 12, 2015 by bugged (see edit history)

[AVS619]

Hello bugged. Thank you indeed for the information, I appreciate it. Yes John at ATS and Mike at Zenith are great and very helpful. They spent quite a bit of time with me on the phone teaching me and helping me select a possible carburetor. But they left it up to me to pick which throat size to use and which mm venture to select. I am not sure if a 1/8th total or 1/4 total drop in throat diameter will make much difference as the modern carbs are more efficient than the original but the venture size make me unsure. Am I wrong in

thinking that if the venture is 'big' (say the 24mm but even the 21mm) that this could be 'corrected' by adjusting the needle valve to lean it out a bit to compensate for the little more fuel? That is what I think is correct but I could be wrong. Any advice?

[Guest bugged]

Hi again.  Believe me I am no carburetor guru.  However I would go with the smaller venturi.  If I looked up the correct picture of your engine the intake runners are long and thus the fuel mixture would not have manifold heat to help the fuel vaporize.  I think the performance of the car will suffer if you try to compensate for an oversize carburetor by leaning it out.  My experience with that needle valve is that you are going to have a flat spot and the engine will gag when you try to accelerate with that thing leaned out.  I think you will have better adjustability with the smaller carburetor.