4 stroke venturi adj. Think this will work?

[Bob Reeves]

Was looking at the Saito on my Score trying to come up with an easy way to make an adjustable venturi. With a Tom Dixon venturi, piece of wood and 1/4-20 nylon screw, I came up with this. Right now it's just tacked in place because If I do it I will add a second piece of wood closer to the venturi intake to make sure the screw doesn't vibrate and cause inconsistencies.

So what do you think, will this work? Wished the screw was 1/4-28 but I don't have any 1/4-28 nylon screws..

[Joe Gilbert]

Bob looks like a great idea .

[RC Storick]

Looks like it will work to me anyway.

[Bob Reeves]

Finally had good enough weather to put up a couple flights on the Score today.. Mickey Mouse adjustable venturi worked like a charm...By golly I think I have a stunt ship on my hands. Wind was about 10 MPH and the Saito was solid as a rock.. Adjusted the screw to a lucky guess that was pretty darn close. 5.3 second laps, plenty of power and no sign of rushing on the down legs, even through consecutive hour glasses.

I'm convinced this engine will be every bit as good as my 40a with just a tad more tweaking.

[Jim Kraft]

Hey Bob; Looks good. What prop are you running?

[Dick Fowler]

Bob, when I think about it, what you are doing is beautiful in it's simplicity! I've tried to get the right speed by dialing the mixture on a Saito .30 and this just isn't the way to do it on a Four Stroker. With the mixture method, either it's too rich or too lean or even both sometimes! No matter where it's set the engine just isn't happy.

I like you method. Set the mixture for an optimum fuel mix which makes the engine happy and vary the power output with your throttle device. Maybe the guys who advocate using the carb may have it right after all.

[Bob Reeves]

Jim,

I am still running a Bolly 13-6 but not sure if it will be my final choice, as the weather starts getting better I am going to be doing allot of experimenting with different props and venturi settings.

Dick,

Yes you need some means to throttle the engine. Problem with an RC crab is consistency, some will work but most have enough tolerance built in that you can't get the consistency we need. If the barrel isn't a perfect fit you have a variable air leak. Besides CL engines ain't suppose to have throttles

I spent almost all summer last year experimenting with a Saito 40a that I was not happy with. After getting quite a bit of help and hints from the Dallas gang I came up with what I believe is the holly grail to making a 4 stroke work.

After-market venturi from UHP or Tom Dixon, YS 20-20 fuel, high pitch big prop, nothing less than 6 pitch and as big as the engine will swing without overheating. Adjust the needle so it is just on the rich side of peaked. If you try to run it too rich it will act just the opposite of a 4-2-4 two stroke and don't think I need to explain what that does. If you try to adjust flight speed by going to a lower pitch prop it will sag overhead and loose speed in the corners. It may sound happy but your flight performance will suck.

You MUST provide some means of being able to adjust the venturi size, on the 40a I stuck a 10-24 nylon screw through the side of a UHP venturi, and the above picture shows what I did with the 56. Interesting phenomena.. as you screw in the adjustment, and re-adjust the needle (remember to keep it just on the rich side of peak) the fuel mileage will go DOWN.. Ya I know I didn't believe it either...

What you are doing is improving the fuel draw and letting the engine run where it has the most torque and putting out the kind of power we need. My 40a is swinging an 11-7 and using a full 4 ounces for the pattern. I have a Saito 62 on the way and will use a UHP manifold with a nylon screw through the side. I fully expect that engine to turn a 13 1/2-14 - 6 or 7 and fly anything I am willing to hang on to.

I also have a Saito 30 that had all the above problems when I thought an 11-4 was the right prop.. When I get a chance I am going to build the Primary Force short kit I have and give it another go. Except this time I will start with a 10-7. If I knew then what I know now I probably wouldn't have replaced it with the Saito 40a. At the time I thought it just wasn't a strong enough engine for what I was trying to do, now I am convinced it was my setup and not the engine...

There I have spilled my guts, now you know all I know about 4 strokes...

Almost forgot, RC clunk tank on muffler pressure and if you can run it on it's side.