Primodus

My Feedback: (56)

I'll be blunt....

Saito FA-72
12x8MAS 3blade
15%/20% fuel

Idle is smooth at 3500-4000 RPM (GloBee tach set on 3 blade) will go lower with trim but it starts to shake quite a bit. Transition is OK until it reaches last 3-4 clicks of throttle and it starts to drop RPM. Low-speed needle is exactly one full turn in from flush, high-speed is four full turns out.

I can run the easy 2 strokes, but four stroke tuning has always eluded me. Now that I have an interest in scale-type birds, four strokes are the only choice IMHO. I throw myself at the mercy of the forum for assistance. Thank you.

w8ye

My Feedback: (16)

Sounds like your low speed is in too far?

Engine should idle down around 2500.

Back out the low speed a little and see what happens?

Primodus

My Feedback: (56)

If I back out the low speed, it sputters and quits. Another tidbit of info that may help, no matter what, if I remove the glow starter, the motor runs rough and dies. I will change the plug from the original to an OS-F and retry that as well.

w8ye

My Feedback: (16)

If your engine continues to not run without glow heat after you change plugs, you might try some new fuel?

Primodus

My Feedback: (56)

Only reason I doubt fuel is the age of it is low.

NM2K

My Feedback: (14)

You didn't mention your experience level, although you did mention that you run two-strokes with no problem.

My Saito .72 idles well at 2,200 rpm. I could get it a bit lower, but then it becomes iffy.

From what I have read here, the .72 was the first of the recent Saitos to run a more radical cam profile. That would
account for the increased idle speed, to some degree.

I've never had consistent good luck with any four-stroke plug other than an OS Type-F. Be sure to check for interference
between the plug tip and the top of the piston. If in doubt, run two washers.

Other factors include fuel, as mentioned previously by another poster (new does not mean fresh unless you got it from the manufacturer),
insufficient prop mass (poor flywheel effect) and poor glow plug choice. This is usually a problem when running wood props that are at the
bottom of the size recommendation and without a spinner. Air leaks at the intake manifold/head junction can also cause weird running
characteristics and are not uncommon, as well as dried/defective o-rings on the needle valve, if employed.

Ed Cregger

Hobbsy

My Feedback: (102)

Prim, what is your top rpm, the 12x8 three blade is a pretty heavy load for setting up a new engine, a 12x8 two blade would make the job much easier. With that heavy of a load the airflow velocity through the carb is low, reducing fuel draw and making it difficult to set the top end lean enough to be able to set up the LS needle.

speedster 1919

My Feedback: (3)

I agree with hobbsy TOO MUCH PROP Go down 1" Thats about a 1.00 prop. Making you run alittle hot and lean..............

jaka

Hi!
It is as easy to set a fourstroke as with a twostroke...by ear!
To me it sounds as if you haven't adjusted the low speed needle (idle needle). You have to listen to how the engine sounds when you do it , not go after how many turns the needle is turned or has been turned.
You also run a too big prop! Put on a two blade APC 12x8 or 13x6 and see the difference.
An OS F plug is also good.

Regards!
Jan K
Sweden

Primodus

My Feedback: (56)

Success! After changing to an OS-F plug and adjusting both needles AND changing the prop to a 13x6MAS two blade I finally managed to get the Beast to run consistently. It was already getting dark in the backyard, so the tach was non-functional. Also, I am gonna keep the idle up a bit until I get more time on it. Transistion is now smooth and very responsive as well. I have the feeling the plug made the complete difference since it stayed running after I took off the glow starter, unlike the other plug. I am going to go back the 12x8 3-blade and try it again tomorrow.