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Engine basics => Engine set up tips => Topic started by: mccoy40 on June 14, 2021, 09:28:30 AM
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All,
I was setting up my plane with a RC version of the OS 40 LA. The carburetor throat looks to be very narrow in comparison to the OS 25 LA Venturi that I have.
I know that having a smaller throat diameter helps cure the runaways, so I was just thinking of keeping the Carburetor and wiring it open.
It should be easy to change out to the OS 25 LA Venturi if the RC carb causes any issues.
Thoughts? S?P
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All,
I was setting up my plane with a RC version of the OS 40 LA. The carburetor throat looks to be very narrow in comparison to the OS 25 LA Venturi that I have.
I know that having a smaller throat diameter helps cure the runaways, so I was just thinking of keeping the Carburetor and wiring it open.
It should be easy to change out to the OS 25 LA Venturi if the RC carb causes any issues.
Thoughts? S?P
That what you see is kind of an illusion. Remember, that there is no spray bar in the way choking down the throat of the carb. I have a model that I can fly with both R/C carb for profile scale and switch to a venturi to fly stunt. It gets much lower fuel economy with the carb wired in place. One thing you can do with the carb is wire off the throttle barrel where it is only about 3/4 throttle or a bit less and then set your needle for the run you want. That will simulate the choke opening of a venturi and NVA spray bar, and you can play with that a little bit. I have a .250" venturi and an OS NVA in my venturi set up for it and get great runs with this and use 4 ounces of fuel for the pattern. The carb body can still rattle some and leak some air around it. You will probably be happier with a real venturi and NVA.
Type at you later,
Dan McEntee
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Ahhh....! Didn't know that there wasn't a spray bar in the rode in the R/C carburetor. At first glance I was think , "MAn this is a small throat!"
Now it makes sense.
Thanks for the info.
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In case you tend to crash often, the longer throttle will be more likely to break the crankcase casting. A Delrin "venturi" is much more forgiving. D>K Steve
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Steve, less likely to break if RC carb is turned and mounted approx 45degrees, especially with RC carbs with needle valve. They usually survive a crash without damage.
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Yes, it works.
RC carbs have more opportunities for air leaks; if you get inconsistent running my first suggestion would be a venturi.
What Dan McEntee said about adjusting the throttle down. Most of the carbs I've used will be at full throttle if you screw the idle adjustment screw in all the way -- I like to use that as a nice hard stop for the throttle.
On the 46LA and Tower 40, you can do a lot of good by tuning the venturi size -- if you try to regulate the plane speed entirely by the needle, you can either end up with slobbery rich runs that turn into screaming runaways half way through, or (if the venturi is too small) runs where you have enough power in the level and the engine fades out in maneuvers.
I adjust my venturi size so that the plane has good pick-up in the maneuvers, but isn't so rich that it wants to run away, or I have to struggle to get the needle set correctly every flight.
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Go with a venturi from Lees Machine Shop and needle valve assembly from Randy Smith and solve 90% of most run problems and get consistancy,