Bob,
I have my Saito 40 on a Sig P-Force. I am using the standard carb setup, with a clunk tank plumbed as a uniflow, opened to the atmosphere. Currenty I am running Wildcat YS 20-20 fuel (all synthetic lube). Prior to this I have used various Sig Champion Fuels. Propwise I am running a black Magnum 3 blade 10-6. Can't use a 11-X or longer 2 blade because of clearance problems with the plane, although I could probably change some things with that.

With the throttle full bore, I was getting pretty fast laps (4.5 or so) and was experiencing similar problems as you describe--the engine seemed "listless", sometimes rich, sometimes lean (during the same run). Yesterday I closed the throttle a little, and now am getting lap speeds around 4.8-5.0, a little more manageable with decent overhead tensions. I think the engine run is better, but still not what I would call "stunt perfect".

I am thinking the problem is related to poor fuel draw. When I look at the carb, intake manifold, and that magnificent 90 degree bend into the head (and thru the intake valve), I am thinking that the pressure drop at the spraybar is not overwhelming since air velocity thru the intake may not be super high. That may  be why closing the throttle seems to have helped some. Recall that this is an RC setup, and for that application, muffler pressure is simply assumed. I am thinking about hooking it up. The main disadvantage for me is that with muffler pressure hooked up, it is real easy to have a self-sustaining backwards run (muffler is the carb, intake is the exhaust), unless you run an electric starter which practically guarantees a forward run.

I know you have the UHP venturi, but I wonder how much fuel draw you are getting with that. It would depend upon the hole size of course and the spraybar diameter. You might also try muffler pressure to see if that makes the run happier.

It is also possible that the engine hasn't completely broken in yet. I don't have a lot of time on it, and Saito's are notorious  for long breakins.

Hi Bob; I have never run 4-strokes in C/L, so don't no much about it. I have run alot of them in R/C however. One thing I would try is going to a 6-pitch prop, and enough diameter to load it enough to get your lap times decent. My experience with 4-stokes was that they like a lot of prop load to run steady. Just my 2-cents.

Hi Bob; I have never run 4-strokes in C/L, so don't no much about it. I have run alot of them in R/C however. One thing I would try is going to a 6-pitch prop, and enough diameter to load it enough to get your lap times decent. My experience with 4-stokes was that they like a lot of prop load to run steady. Just my 2-cents.

Boy did you hit the nail on the head, have been listning and posting to Brad Walker over on UHP.. check out this thread.. http://www.egpworld.com/forum/default.aspx?f=2&m=19040

Why not post them over here?

Bob, those Dallas guys know 4 strokes and Saito in particular. They have bene experimenting with them for a long time. the guys in the Northeast also. Don't give up theres light at the end of the tunnel. . Ron.

Hi Bob, Prior to the terminal prang which my ARF Nobler with my Saito .40 suffered at the Brodak FlyIn, I ran it with an APC 10 X 4 and YS 20 20 all synthetic. It pulled like a mule and gave me a full measure of pleasure. The tank was Sullivan with uniflow configuration running on muffler pressure. I shorted the tank for its final flight after it finished its next to last flight at 7' 59''! I only took out .5 oz. but that was enough for it to quit in the first loop of the four leaf clover! I am still saddened just thinking about it! Phil Spillman

Think this will be my final setup, after 14 flights over 3 days it has proven to be pretty darn consistant.

Rev-Up 11-7, Powermaster YS 20-20 fuel, OS F plug, RC Clunk tank conventionally plumbed on muffler pressure. UHP manifold with adjustable venturi via a 10-32 nylon screw through the side.

Have the venturi set so peak RPM is 81-8200, needle just on the rich side of peak. Initial lap times on 58 foot lines 5.1 seconds, speeds up a little as the fuel gets low to 4.8 just before it quits. Runs 6 minutes 3 seconds on 4 ounces.

With the adjustable venturi I can adjust the engine RPM from about 9 grand to something below 7800, I stopped at 7800 as the air speed was too slow for the airframe. At full bore it was doing 4.2 second laps, started cranking it in and readjusting needle as I went.  Putting up test flights about every 100 RPM, consistency of run was solid at all settings and speeds.

Sure a world of difference between what I started with (11-4 Rev-Up and 10-22 50/50  fuel) Most of the ideas for the final setup came from communications with Brad Walker from Dallas.. Thanks Brad...