The Stovebolt Site Forums The Shop Area Engine Shop Model B power piston spring

According to Mikes Carburetor the power piston spring is no longer available. However I found a kit that includes the spring (about the size and twice the length of a ball point pen spring). The companies name is "The Carburetor Doctor" in Canada but, they don't ship out of country. If I get desperate would it be possible to have one of our brethren order the kit and then send to me. All expense paid plus your time. Oh by the way it's kit #CK10, $34.42. Doc.

Doc, there are dozens of kits available on Ebay, with springs about that size included. Most of them are less than $20.00, some a lot less. I'd be tempted to try to use something like that, and adjust the length if necessary to get the right tension and range of movement. Another source of compression springs is Brownell's gunsmithing supply in Montezuma Iowa. They stock a wide variety of springs in various diameters and tensions that we gunsmiths use for detent ball springs, etc. I believe their usual stock size is about 3" in length, and the spring is cut to fit a particular application.
Jerry

Thanks Jerry, I checked the last one that I had and my gram meter read 16. I will contact Brownell's, due to it being a compression spring I should stick close to the same gram pressure shouldn't I ? Ed

There are a number of different springs for the various model B's.

The correct ones come in the better carb rebuilding kits. Tag number required.

Jon.

It should be possible to tune the power valve response to kick in the full-rich point to a particular manifold vacuum reading by altering the length and/or tension of the spring. A weaker spring will allow the mixture to stay lean longer by restricting fuel flow to the main jet only at a lower manifold vacuum. Once the vacuum drops below the point where it can hold the piston in the up (lean) position, then the piston will drop and force the power valve ball off its seat. That allows fuel to bypass the main jet and put the carb into its "full rich" mode. Stronger spring = richer mixture at higher manifold vacuum.
Jerry

Jerry - one of the many things Carter did to allow tuning of their carburetors was to produce a number of different step-up piston springs. Within reason, the various Carter type YF carbs used on Chevrolet engines can use Carter AFB step-up piston springs, which are widely available.

The Rochester B springs are significantly longer than the widely available Carter ones. We had to expend considerable funds to have the various Rochester B (and 2G/4G) springs reproduced.

Jon.

One possibly related annoyance I have with my model B is the barely above-idle throttle position:

When throttle is opened just slightly above idle, the engine runs super lean 18-19:1 afr.
Idle mixture is tuned ~14.5 and mid to full throttle cruise is slightly rich ~13.5 afr.

It's annoying when starting from a stop since the engine is super lean whenever I'm trying to feather the clutch.

I wonder if the problem could be solved by installing a bigger jet, and compensating with a weaker power piston spring?

Jerry, I just contacted Brownell's and they are going to find something to meet my specifications. Thanks again. I ordered all the springs for the YF, AFB, etc.about a month ago. I'm sure Brownell's will come up with something, if nothing else I will order the rebuild kits, I can always use the other items in the kits. Ed

If there's ever been a bunch of guys who are into more oddball tinkering than hotrodders, it's probably custom gunsmiths, and Brownell's has been the industry standard in keeping us supplied for about three generations. They're also a bunch of really good guys to deal with!
Jerry