A friend is flying a pattern ship with a Saito 150 on the front. Until a few weeks back everything was fine. The flight was easily completed and with a totally reliable engine. Unfortunately the engine appears to have gotten wind of the upcoming UK nationals in which he is competing. The engine now cuts without fail every flight, to the extent that he is now afraid to fly the plane for fear of doing serious damage.

The symptoms are as follows. Take off and fly the circuit on about half throttle. Reducing the throttle to idle and then attempting an increase of the throttle setting causes the engine to cut. This is with the plane in a level circuit. It will also cut when throttling up after a loop or similar. The problem has us stumped really. Initially the problem could be replicated on the ground by nosing down the plane for the duration of a downline and then throttling up. Richening the low speed needle has cured this, to the extent that it will run perfectly on the ground for a whole tank of fuel.

The setup is as follows:

Saito 150
Baffled 4-Stroke Pipe Exhaust
Coolpower 15%
OS 'F'
APC 16x8
Soft Mounted
Running 8800rpm on top end, 2800rpm idle.
Tank is inline with carb and is 16oz.

We have: replaced Glow Plug, replaced Fuel line, added a header tank, tightened engine mounts, fiddled with needles. Settings are now approx 2.25turns open on the high speed, low speed needle setting unkown, but just out from flush IIRC.

Three of us have been working on this, but we're stumped He's got some CP30 for competition use, and I'm tempted to try that next and see what effect it has.

Any ideas guys please? The Nationals are three weeks away today, and he's getting kinda worried now.

Cheers


Chris

Welcome to the Saito dead stick zone.

I have had the same problem with all of my Saito's. I have loved the way run. They have been my best friend and then,,,,,,,



Oh no,,, why,,, why now,,,,,,, of all the times they have run without the slightest adjustment,,,,, and now,,,,,,,,,,,,,,,,,,,,,,,,,,



Crunch...

Saito man no more. Maybe it's me but I have a bad taste and will go with YS from now on

.

If that's the best idle you can get, the low end isn't tuned right!

low speed needle setting unkown, but just out from flush IIRC.

Do you mean that it sticks out past the control link.
If so at that setting it should be to rich at the bottom end.
It should be just in and it should idle at 2000 easy.
Also is the clunk stuck foward.
Good luck and hope this helps.

Well I'll try and give my opinion here. A few years back several members at our club had problem after problem with the Saito 150 doing this same thing. It got to the point that no matter what they did there seemed to be no cure. I believe the problem was the carb sucking air and going way lean after a few minutes of flight.

This is only my opinion but I would try a couple of things.

1) Install Enya #3 plug

2) The 2 1/4 on the high end doesn't sound right usually 3 turns is the norm.

3) Look at o-ring on needle valve or replace it, after a few years they will detereiate (spelling?).

4) If all else fails maybe try an on board glow.

Sometimes going back to the basics is best with problems like this and usually it's something stupid that you never thought of.
Good Luck!

saito's always give off a distinctive ..."bucking"... when they are too rich at idle ! It should idle smooth as silk at 2000 rpm ....should idle even lower if mixture is right-on!!

maybe try a new plug and adjust the valves?

Get a simple 2 stroke. Take life easy. Captin John

you might try adjusting the high end needle until max RPM, then back it down about 3-400. After that bring the engine down to the slowest Idle that runs consistantly. Then turn the low end needle in until you hear the RPM picking up. at this point turn the needle about 1/16 back rich and test the transistion. Best of luck to ya.

Phil (Mesa, AZ)

If the carb is clean and needles are set to where you feel they are right. Then as rc34074 has said, "check the valves."

I had a friend with an OS 91. Terrible trouble comming from idle to full power. He set the valves and it is a different engine now. Runs super.

Chris,

Check to ensure that the main needle venturi assembly is screwed in tight to the carb body. Mine backed out when I was breaking it in on the bench.

The problem you describe sounds to me like a too-rich low end. But since I don't have any Saito experience (other than an hour on the test stand), better listen to the guys who have been running them for a while...

Steve

Thanks for the help here! We have made some progress today despite the *AWFUL* weather. Richening the low speed needle had allowed the engine to keep running through the whole rev range. Only problem now is that it is soo rich that transition is not so good. Next step IMO is to richen the high end more and then lean the low to compensate. Hopefully we'll be getting some practise in the evenings this week

Cheers


Chris