Thursday, July 18, 2019

Missing dimension on Throttle plans?

Q: Hi Allen.  I recently purchased plans for the 2 Jet throttle carburetor.  On page 2 in the front view, hole # 5 & 6 I need a location for.   I couldn't find it on the drawing.  Is #6 hole for the set crew for the spray bar?  I understand that the carburetor can be enlarged for bigger engines.  What formula do I use to enlarge it for a 2 1/2" bore slow speed engine?  Thanks for your reply - Norman Stauffer

A: Hi Norm.  If Dad were still alive, I'm sure he could definitively answer your questions.  I was a computer programmer/analyst by trade, but do have some mechanical skills, so I'll give it a try:

I believe hole#5 location is shown in the "Left Side View", the center being .270" from the top, and .505" from the bottom.  Hole#6 is simply aligned with hole#5 and drilled all the way thru.

I must admit these plans are a bit of a challenge to visualize because of the odd shape, plus all the holes and passages.  I surmise that once you build the main "block" and drill the large cylinder holes
that the smaller holes and details will be easier to ascertain.

To answer your last question, according to paragraph 2 of Dad's construction notes, the throttle bore should be 25% of the piston diameter, so for a 2.5" bore engine, the throttle size should be .625

Hope this helps...


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