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What is the advantages and disadvantages of the different size stuffers (tall vs short)?

Short are for 101's and long are for 91's.

Dennis,
The larger the fingers on a stuffer means that it will take up more space in the crankcase, or as it implies, stuffs the crankcase. When the piston moves down the cylinder, that motion builds up pressuse in the crankcase and as the piston passes the ports and the ports open, the combustion area will get a more positive and powerful charge of fuel. So, if you are building a 100cc Mc, it is best to use a long finger stuffer. The 101's did have short finger stuffers in them. Stuffing the crankcase will effect the carburator's operation, also... Hope this will help out...

The stuffer I have for my 91b1 has the numbers: 58139A embossed onto the bottom of it. Is this the right one (tall stuffer) for the engine?
Thanks for the info on stuffer function. Makes sense. I thought maybe the design of it may also have something to do with the crank forcing the flow a certain direction.

Run as much stuffer as you can fit.

Years ago when my son was running Jr. Sportsman with an 820, WKA forgot to put in the dimension from the centerline of the crank, to the bottom of the crankcase one year.
Upon finding this in the rule book, all our 820 blocks went right to the mill, and I shortened the block so that the stuffer was within .040" of the crank.
(about .100 cut if I remember correctly)
They run much better.
Unfortunately, WKA discovered the omission the next year, and put it back in.
So I ended up with a bunch of illegal blocks.......

You naughty naughty boy Gordon sounds as if you needed time in the naughty corner for doing that one.

Mc Bob.

Any loophole that can be used to advantage will be used. That's just the way racers are.If it doesn't say I can't do it that means I can until I get caught.