Paul or anyone. Looking at the Kinsler racing goods catalog I noticed that their butterfly throttle fully closes 14 degrees before perpendicular. Is this design point to keep it from jamming when shut? Obviously the throttle plate then will not be perfectly round but an ellipse. Also does a throttle have to completely close? Cold starts may be one reason perhaps but that is not such an issue with programmable injectors. I am concerned because the high vacuum forces on the throttle plate may bend it unless I chose stainless.
Doug in Japan.
Yes that is what it sounds like to me. Usually throttles don't close completely as the engine needs air for idling. The carb idle adjust screw changes the throttle opening during idle. Not to be confused with the carb idle jet screw.
Kinsler has some neat stuff so everybody should download their catalog. http://www.kinsler.com/page--HandbookCatalog--2.html Particularly useful are their bell mouths for intake runners.
Paul Lamar

Many FI systems used to have idle air bypass - allowing the throttle plate to close completely. Air through the bypass is controlle
d by a separate (sometimes feedback, temperature adjusting, solenoid operated) valve.
Regards,
Matt-
Guys Thanks. I'll go ahead and make up a butterfly valve on Friday. Everyweek I am logging ten hours in the school machine shop and it is finally paying off. Some parts however are faster to make from a rough sketch and then cut to fit then pre design if you know what I mean. Real world meets design world sort of thing:) Those parts will be documented after their dimensions are fixed however.
Doug in Japan
Doug,
All current butterfly carbs are set up to prevent closing to 90°. Several
reasons for this, the first you got right off, to prevent jams. Second; and
similar to the first is to prevent damage in the event of a backfire. It
also prevents the linkage from going over center and trying to open the
wrong way. Lastly, the closer the butterfly is to vertical the more variable
the plate position will be at idle. Most carbs have a series of holes near
the closed point to control the idle mixture better. Those holes need to
open in the proper sequence to transition properly. If on the other hand if
you are making a throttle body it is as critical. I would still go with a
slight angle, it will work mor
e reliably.

Bill Jepson