The Stovebolt Site Forums The Shop Area Engine Shop Carburator problems on a 261....

Good day gentlemen

Hoping to wake up Carb King and other Gurus with this one. I may have exceeded the design of my carburator.

Basic specs.

Stock 1940 Chev 4x4 Canadian Military Pattern.
Original 216 W-1 carb replaced with 1959 261 total stock rebuilt with a stock 261 stock jetting Rochester B. Carb recently rebuilt and flow tested by professional. Engine never ran better or sweeter.

Engine and rolling chassis gradually being worked out in back field to finalize all the silly little adjustmnets before I install all the sheet metal.

Problem is the carb is flowing raw gas when I drive in extreme condition and I am concerned with fire hazard.

I was climbing a 12 foot tall and steep wood chip pile at about 45 degrees++ using just a fast idle...pulls like a tractor.... when I noticed raw gas flowing off the back of the carb. I don't think my float is badly adjusted as it runs well otherwise and I hesitate to take it apart to reset the float and find out it is now too low for normal driving.

Have I exceeded the design of the Rochester carb or is there a solution....?

Is the Rochester B carb vented differently and not suited for this kind of crazy driving...?

Makes me wonder how much better the original Carter W-1 carb would have faired in similar situations....after all the original carb on a 216 did pull the fully dressed vehicle up a 45 degree incline at the testing ground... I have also driven M 37 Dodge in similar crazy conditions without noticing any gas overflow.

I know there are special carbs for serious rock climber that prevents this situation but I am not prepared to stray too far from stock in an historical vehicle.

Your advice comments will be appreciated.

Bob C.

The Roch. model B would not be well suited for this type driving.
The fuel level is almost to the top of the bowl & they are nortorious for warping & leaking out the gasket. Even if you leveled it out & sealed it good I think you will have flooding problems.

The W-1 used on the Canadian military vehicle had some special items for extreme conditions. The Rochester B does not have these items.

There are no Carter W-1 carbs which, unmodified, are sufficiently large to feed a 261.

If originality is of great concern, and cost is of little concern, a W-1 could probably be modified to flow sufficient air for the 261, but I wouldn't want to be the one doing it at this point in time.

My "love" for the Rochester type B is well-known.

At first blush, nothing comes to mind that would be a suitable extreme substitute, but some version of a military Zenith from a 270 could probably be adapted. Since Carter offered a steep slope kit for the YF used on the Willys Jeep, a larger YF could probably be adapted.

Lots of homework is in order.

Jon.

Thanks Jon

You have confirmed my worst fears..... now that I have found a good working Rochester B carb I will have to stay on the parade ground. Now that it is fully rebuilt it is not even leaking around the top gasket.....but sure pours when tilted..!!!!

Can you point me in the proper direction as to a YF..... any carb number to suggest that I could start hunting for...?
In fact I do have a few YF in the shop that I accumulated over the years maybe...just maybe....

I may also focus on a GMC 270 military carb as a friend of mine has all the shop manuals for that period...

Part of my problem is the throttle linkage has to go around the front of the engine, over the water pump down under the manifold to the original bellcrank pivot than to the carb has the truck is right hand drive.

Will keep you informed of my trials and tribulations...

We plan to build a jig to mount carbs for testing on a spare manifold....load the bowl with gas and gradually tilt the manifold frontwards and backwards and see it they leak and record the angle...
Will start with an old W-1 to try to set a base line....

Thanks for your help.

Bob

Best choice would be 879s. There are others not quite so close.

Jon

Some late hours on the WWW produced a source for a Zenith.

Searching old shop manuals should that GMC 270 truck engines... including military 4x4 WW II eninge use a Zenith 11275 carb.

Seems a replacement Zenith is still manufactured ...brand new... that will bolt right on the Chev 261 manifold and will even accept the standard 1940 air filter. Basically the NOS is a 28-228 Zenith that has provision for adapting the venturi size requirements to engine c.i. and an adjustable external fuel mixture valve under the main bowl.

The bad news is they are expensive at $625.00 I am told the Zenith will tolerate extreme driving conditions/angle of attack without leaking its precious gas content.

Seriously considering asking Santa for one at Xmas..... or sooner as I have been a very good boy !!!

Comments Jon or other carby officinados !!!!

Stay tuned.

Bob C

Some of what you posted in this post incorrect:

"Searching old shop manuals should that GMC 270 truck engines... including military 4x4 WW II eninge use a Zenith 11275 carb." - NOT TRUE. The 11275 is a universal replacement carb, never original, that may be used to replace SOME original carbs used on SOME 270's.

"Basically the NOS is a 28-228 Zenith that has provision for adapting the venturi size requirements to engine c.i." - AGAIN, NOT TRUE. The 228 series Zeniths come in a variety of internal venturi sizes, but one should not attempt to change the venturi in any given carb, as pressed in airbleeds will be incorrect for the different venturi.

Jon.

Hi Jon

I bow my head to the expert and stand corrected.... 11275 is a Universal alternate..... OK

...and the 28-228 comes manufactured with various venturi inside guts that are permanently installed..... but I understand that specifying the engine size they will match what I need.....Jon will there be another ## on the carb that will relate to the 261/270 cu. inch displacement...?

I am still wondering if the design of the Zenith will be less prone to leaking in steep hills/extreme driving angle .......

Distributor recommended the Zenith over the 4x4 Weber 2 barrel when I explained that I needed the bottom end torque more than top RPM..... 6:13 axles x 2 speed T case and bull gear around 7.058 and a top speed of around 45mph in high gear.... and with 1938 brake design who would want to go faster. My goal is never to go over 3000rpm....

Am I on the right track Jon...?

Bob