Well, now after all this, I am thinking it just may be worth a try! Why? Well, why not? What is the worst that can happen? On another note, however, season is over here now anyways, so will not get a chance to try it out till spring anyways. With an incomplete carburetor, the engine is useless as it sits anyways. First step is to look and see if I can find the control line needle assembly that I had planned on using should I go through with it.
Now to just figure out how big a hole/venturi to make the adapter. For simplicity, I will probably make it just a straight equal diameter hole right through, as I am still new to thsi stuff and this way would be easy for me. Thanks all for the help and suggestions.
Well, as a suggestion, if you have another venturi, just make it look like that one. Measure the diameter of the carb mount on the engine, and how far down you will need to go. Stop about 1/16" above the crank shaft. That will be the OD of the base of the venturi. Now just figure out how big the OD of the main body should be, and how tall. Again, you can look at another one and make it look about right. As for the inside hole, 1/4" (or .250" ) would be a good place to start for a .40. You can always drill it out, or change your spec if you print more. The hole should be that diameter where the spray bar goes through. Everything about it can look like a funnel. That helps with air velocity and makes for better atomization. Again, just make it look like your other sample. When finished, see how it fits, and adjust where necessary. Go to the hardware store and get some O-rings to act as a seal between the shoulder of the venturi and engine case. When you drill it for the spray bar, you need to push down on it a bit to compress the o-ring. If it comes out a bit loose, make some paper gasket shims to go on the venturi before the o-ring to take up the space, or try a thicker o-ring. A dab of silicone will help seal things just in case. When you assemble everything, make sure the hole is somewhere in the middle, and pointing down the venturi so you can't see it. You can then mount the engine on a test stand and see what happens. As mentioned, the venturi is quite cool while the engine is running but when it stops heat will creep to the prop shaft, but at the same time, the whole engine is cooling down, so it may not get too hot, you'll just have to try. If you are using a true venturi set up, like some Magnum engine have, where the spray bar goes through the hole where the pinch bar that holds the carb on, you need to make the ID much smaller. I think Randy Smith may have a chart posted in the engine section, but I'm gonna guess at about 5/32". This is because you have no spray bar to create a restriction to help with crank case vacuum to draw fuel, so you need a smaller hole or throat in the venturi. You will need to drill about a 1/16" hole through the side of the venturi so that it lines up with the hole in the engine. When all is said and done, the best case is that the PLA material will work just fine. The worst case is that it will get a bit soft and distort, but at least you will have figured out what you need to know to make venturis using what you have on hand, and you can then purchase what you need for material. Let us know how it all works out. What else you got to do all winter!!???
Type at you later,
Dan McEntee
Topic: 3D Printed Venturi? (Read 1868 times)
