How do you tune the carbs on a '37 V12

[Ty Stinson]

Hello. How can I tune the carburetors on a '37 Cad V12? The engine starts easy and runs smooth. But, if I goose the accelerate there sometimes is a hesitation and a small (not loud) backfire.

Ty Stinson
'37 8519 sedan
CLC 22330

[Frank Starr]

This is almost certainly not a simple carburetor tuning issue.  Rather, it is a result of the accelerator pump failing to operate properly.  The accelerator pump must instantly inject a stream of fuel into the carb at even the slightest opening of the throttle.  Otherwise, the fuel mixture suddenly becomes very lean as a result of the throttle opening, causing the hesitation and backfire. 

There can be several reasons for the malady.  Start by rebuilding the carburetor.  It would of course be nice if you could get a new accelerator pump.  If not, you must be sure the pump seal is good (I don't know what pump design theis carburetor has).  If it doesn't seal, you're wasting you're time.

Just as likely, and what I invariably find on older cars with higher mileage, is that  the mechanical linkage connecting the pump to the throttle is worn, with noticable free play (what the British call 'lost motion').  So when you open the throttle, the initial motion is 'lost' before it reaches the pump.  To repair this, you must get clever.  Usually, you'll find that linkage holes have enlarged, the linkage shafts are worn where they fit in the pump or throttle arms, or some intermediate shaft in the linkage system is worn.  If you're not clever with tools at this kind of work, you'll need to find a GOOD carburetor shop.  (No, I don't know any, I do my own.)

Hope this gives you an idea.

Frank Starr, P.E.
CLC Member and former Director
Seattle

Hello. How can I tune the carburetors on a '37 Cad V12? The engine starts easy and runs smooth. But, if I goose the accelerate there sometimes is a hesitation and a small (not loud) backfire.

Ty Stinson
'37 8519 sedan
CLC 22330

[Mark]

Ty

Are they Detroit CR51s?  I'm showing p/n 1752 for right and 1753 for left.

[T.L. (Ty) Stinson]

Thank you Mark and Frank:

Your comments and information have been very helpful and interesting. I will check out the carb model numbers or type and I think I will let the experts do the work in the spring.

Ty Stinson
CLC 22330