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Another day another question ??

What advantage would a Tillerton HR have over a Mac BDC except possibly spares and diaphrams ............

Mc Bob.

With all due respect to Steve. After 30 years and being a half fast engine builder. I'm not smart enough to figure out a mac carb. I have some that work great ....and some that don't . And I can't figure out why.

I think of it more as a consistancy thing than anything else. Can I get a mac carb to start and run......yep....not much of a problem.......can I get them to "work" on any type of a consistant basis.....forget it!

Rob,

So true.... the one real advantage to the Tillys, whether it be two small or one big one it that they are pretty user friendly and consistent. I can usually make a BDC model carb work very well but there are still occasions where I have problems with them and they need a lot of attention. For a runner in the hands of the average vintage karter who only runs a few times a year the Tilly is just a lot less trouble.
Regards,
Steve O'Hara

On the flow bench, the Mac carb is better, but I have to agree on the inconsistency point about them.
Too many little passages that can be effected by a small stray drop of oil, or atmosphere conditions.
And the needles seem to be much more coarse.
That is, they can go from rich to lean with less of a turn than the Tillotson.
If you want flow, let me build you a annular ring venturi HR (or find one that the late Jack Green made).
It gets rid of the booster venturi, and the 12 annular jets do a way better job at atomizing the fuel.
This is especially important on our little 2-strokes that have only inches between where the fuel dumps in, and where it's burned.
The ones I do have a one piece inlet bell, that extends all the way in, and forms the venturi.

Or if you have access to a machine shop, build one your self.