Re: IML: Carb Problem analysis

[David Whitney <hazegreen66@xxxxxxxxx>]

Regarding the slight stumble off idle, that is a perennial and permicious problem with our Carters.

 

What you are doing when you push the accelerator pedal is opening the throttle plates.  At that point the idle circuit (the tubes that feed air and gas at idle) stops doing its job and the primary circuit takes over.  The primary circuit allows gas to be pulled out of the carb via vacuum through the venturis in the bores. 

 

It's a chicken and egg problem.  There is no gas to drive the engine until you have vacuum supplied by the engine.  On mild acceleration, as from a stop in city driving, the accelerator pump is not a factor.

 

Carter designed a "fix" for this problem called the transfer slot.  If you look down the bores -- this assumes you are either very tall or very agile and can climb inside the engine compartment -- you will see part of a narrow, vertical slot.  The rest of the slot is obscured by the closed throttle plates.

 

The idea is that gas will dribble through the transfer slot when you just barely crack open the throttle plates to help the transition from idle to primary circuit until there is sufficient vacuum to draw the proper amount of gas.

 

Sherman mentioned vacuum leaks and the other usual suspects because those factors can confuse our carburetors when they are trying to supply the proper fuel/air mixture for the driving situation without the aid of any digital device.  Vacuum, gravity and spring pressure are their only means of making these adjustments.  The designers assumed that your pistons, valves and ignition system are all working within specs.  Many a good carburetor has been tossed on the scrap heap and disparaged as "never worked right" when the actual problem lay elsewhere. 

 

When you remove the carburetor to clean or rebuild it, you must blow out all the minute fuel and air passages with pressurized carb cleaner or air and keep them clean during reassembly.  Once that's done, proper adjustment of the throttle plates determines when the transfer slot comes into play.

 

I recently disassembled and reassembled a brand new Edelbrock (Carter clone) carburetor and discovered a tiny scrap of paper stuck inside the transfer slot.  You can imagine the hesitation off idle improved greatly after I removed it.

 

If you "feather" the accelerator on just about any '60s or '70s Imperial, you will feel the precise spot where the transfer slot is doing its work.  Once you know where it is and you are confident your carburetor is properly adjusted, try to avoid that spot in your routine driving habits.

 

If you still can't avoid the bog, the next step is changing your jets or metering rods to adjust the amount of fuel that is available in the primary circuit.

 

Happy motoring,

 

David

Happy motoring,

David

'91 K-Imperial driver
'66 Crown Coupe project
'66 LeBaron dual air and every option known to man

---

Yahoo! Shopping
 
Find Great Deals on Holiday Gifts at Yahoo! Shopping