[TR] TR3 carb throttle shaft

Randall TR3driver at ca.rr.com
Sun Dec 9 18:34:42 MST 2012

> getting ready to finally put the new throttle shafts in my carbs.
> measuring the shafts they are 0.3102"
> 5/16" is 0.3125.
> i know its only 2 1/2 thou but as reams are available in 
> 0.0001 increments im wondering if i should ream under size also?

Don't forget, some clearance is necessary to give the shafts room to turn.
I am fairly certain that the intent was to ream to exactly 5/16" and the
required 'running' clearance is built into the shafts.  The replacement
bushings that I got were already sized to 5/16", and so my 5/16 reamer only
cut on one side where I hadn't got the alignment just right.

I've lost track of just when that was, but it was a long time ago and those
carbs are still working fine today.

In operation, the air leak is smaller than you might think anyway, because
the plate & shaft get sucked against the side that leaks.  The impact on
actual fuel mixture is fairly miniscule, especially since the mixture gets
adjusted at idle (where the air going past the shaft is larger in proportion
to the air going through the venturi than at any other time). 

-- Randall 

More information about the Triumphs mailing list