Saito 150

The only time I have seen something similar, the engine was leaning out in the air. How much RPM is the engine turning on the ground? What prop? Plug? An air leak will cause you fits. Check the carb mounting and back plate screws. Make sure the vent line is open. Adjust the high end by the usual, peak RPM, slowing down the engine 300 RPM by richening the mixture. Once broken in Saito engines are usually rock solid.

1. What size fuel line are you using in the plane? Big Saitos eat fuel and need larger fuel lines AND larger brass tubing in the tank.
2. What type of fuel and prop are you using? What RPM's? It takes at least 1 gallon of fuel on the ground to break in a big Saito and at least 3 gallons until it is completely broken in.
3. Check the carburetor/intake manifold for tightness. Are the fuel lines pinched or kinked? Are you using muffler pressure?
4. Fuel foaming? Check your tank padding. The big Saitos have a lot of vibration. When the tank is completely full it is less of a problem. As the tank empties there is more room for the "Foam"
5. Check the tank for leaks and especially the fuel line leading to the clunk. See if there is a hole in the fuel line where it meets up with the brass tubing that goes through the stopper. If there is, the engine will suck air after the fuel level gets close to the level of the stopper.
6. When you finished your ground run-in did you reset the low end mixture and reset the valve lash? Saitos run very rich in the mid range. The factory idle adjustment is set very rich also. Once you get a Saito broken in to the point it will hold full RPM's on the ground you need to lean the idle mix as much as possible. If not you go extremely rich at anything less than full throttle.
7. Check this site: Mark D. Fain

Sounds like it is too lean.
I get mine idling and lean the low end down until the exhaust smoke comes in puffs rather than a full stream. Then I use a tach to find top end and richen it up until I get a 300 RPM drop on the tach. Doing it by ear generally does not work very well. I have been using a 15X8 APC prop.

richen up the low end needle about 1/4 turn. I've had the same problem with Saitos. Richening up the low end solved it every time.

I tried ALL of these things and then found the low end needle was too lean. Go figger, eh?

To all who replied, Thanks for the info guys. I'm going to run the engine on the bench until I'm sure it's broken in. The deadstick landings are starting to add up. A ding here a ding there......one day I won't be so lucky. I'm going to start with a new gas tank, since the one that came with the plane is to small (14oz). This thing goobles fuel. I suspect the tank is foaming. If that doesn't do the trick I'll move on to the next item. I just want the damn thing to run.
JT.

After it's broken in, you will find that fuel consumption will drop dramatically. I have a 24oz tank, when I first got it, I could get twelve minutes on a flight. It ran out a number of times so I set the timer on the transmitter to warn me after 10 minutes. One day I landed after the timer went off and happened to check on remaining fuel. Had a lot left. I doesn't burn nearly as much fuel now. I bought a YS 1.2 and put it on the same plane to break it in. Spins the same 16-8 prop over 1000 RPM higher. Later Bill