Re: Carter WDO Carburetor adjustment

Posted by DavidPackard On 2023/10/16 21:29:16

Mike;

Assuming you have already gone through the 4 engine tune-up items suggested by Carter, and you have the correct ‘tag number’ carburetor, then the hole in acceleration could be (emphasis on could) the follow two items.

Anti-percolator valve: There is an adjustment to coordinate throttle position to valve closure position. If the AP valve is adjusted such that the AP valve remains open at higher throttle positions the transition from the low speed to the high speed circuits will be leaner than expected. It’s a matter of degree in that if the AP valve is grossly open during transition the engine cannot accelerate above the low speed circuit (about 25 mph in 3rd gear). Much lower openings, including AP valve leakage, will produce a local lean condition that may be detectable. As a ‘war story’, I had an AP valve that seemed to have lost the closing spring tension. Destructive disassembly revealed a corroded spring that had failed. I took apart the other valve and it too had a corroded and failed spring, but that spring had ‘nested’ together and still closed the valve at a lower seat pressure. Note that the 111-19S anti-percolator arm will open/close the AP valve together, but each individual valve is adjustable. With one valve open/leaking and the other closed during transition may result in a minor lean condition limited to 4 cylinders. I currently have a set of sealed AP valves installed as a test, so far I haven’t been let down by the sealed valves, but then again I don’t have a lot of experience in hot restarts. Standard tooling may be used to make this adjustment.

Coordination between throttle position and the minimum metering rod position. This adjustment is conducted with a ‘special’ Carter tool’. The intent of this adjustment is to ‘override’ the stroke of the vacumeter piston as a function of throttle position, and avoid a lean condition. I’ve intentionally adjusted this feature to allow the aforementioned lean condition. What I found is the transition between the low and high speed circuits became compromised . . . stumbled through the range with roughness. From this experience I’ve concluded that the Carter design makes the flow area of the main jet significantly small during idle operation, and then increases the main jet flow area just before main jet flow is required for the transition to the high speed circuit. Depressing the throttle will normally overcome most adjustment errors in this area. I’ve also richened the transition zone with the addition of a shim washer in the vacumeter piston, with would take effect when the minimum metering rod position is not in play.

I’ve not included the accelerator pump in this discussion because you indicated the hole was in the middle of accelerating. Please give us a better idea of when the difficulty is occurring and remember the difficultly may not be carburetor related.

dp