Making ST sprinkler venturies

[Bob Reeves]

Would some of you guys that make your own ST sprinkler venturies mind sharing your trick to cutting and getting the spray bar cut-out in the proper place?

[Willis Swindell]

Bob
I adjust with different size O rings.
Willis 

[tom hampshire]

Hi Bob - Mike the spray bar, select a twist drill of the same diameter.  Turn the crankshaft so the intake port is closed, press the venturi insert in place and mount up in the drill press vise. Drill carefully so as to remove the sector of the insert where the spray bar will go.  Disassemble, clean, deburr and its done.  I would not try this with a hand drill, but it might work if you go slow enough.  Tom H.

[Bob Reeves]

Thought I would get smart and make a duplicate of the engines venturi hole.. Made it out of aluminum and it turned out great (I thought). First time I tried drilling a delrin insert the drill wandered and hogged out the bottom guide hole. This was with it clamped down in a drill press.

Tom, appreciate the thought but sure glad I didn't try this with an engine.

I just ordered a 1/8" round end mill, for lack of a better plan will try clamping the insert to my mill with a V block and cut it by making a couple passes with the round end mill.

[Scott Jenkins]

Depending on how you clamp the venturi you can accomplish the same thing with a conventional endmill. If the hole in your engine is 0.156 then use a endmill the same diameter. You are just cutting the half round slot perpendicularto the diameter of the part of the venturi that is inserted into the engine. I do this all the time and can make a very good approximation most every time. You may find it is easier to turn the diameter of the part that fits in the engine first then cut the half round slot for the needle valve now you can finish the venturi parts above the engine mount and bore the inside to size and shape.

Scott