As some of you may have noted in the past, I was always in favor of using a carb in all 4-Stroke C/L applications. 

Well, turns out I was wrong. Now, before I dig myself in, let me quantify. 
I have ten 4-stroke planes flying at this time, all with carbs, all running perfectly. Having had around 10 other 4-S powered planes, I can claim well over 1000 flights.
 
But, because I have had good results, it does not mean that everyone will. Case in point, Dan Banjock’s Vista. He was having fits with inconsistent engine runs with his carb-equipped SAITO .72. He disassembled the carb and found approximately .002” clearance between the throttle drum and bore. This may not sound like much but it’s a clear and inconsistent path for air leakage. He fabricated a venturi and the runs are now perfect. 

I checked some of mine and found that all the fits were as close as I could hope for, with absolutely no noticeable clearance. The engines in question are three SAITO .30s, one SAITO .50, one SAITO .56, three Surpass 26s, one OS .40 4S, one Surpass .40 and one ENYA .53.

So, others have had problems - will that cause me to change mine from carb to venturi?
ABSOLUTELY NOT!! 

Here’s what I suggest. If you decide to try a 4-stroke engine, run it stock first. Get everything sorted out. If it works, let it be and enjoy. If you cannot get consistent runs, check out my other (future) post on 4-stroke cooling - an extremely important issue. 

If that fails, try the venturi.

Bob Z.

Continued. I then used the stock needle valve assy.

Bob,

I been trying to tell you that for years.  I guess you had to see it for yourself.