Saito FA-125A AAC 1.25cu in 4-stroke Engine Review

Rich Noon takes an indepth look at this exciting new Saito release -- a replacement for the old standby, the 1.20, that is closer in size and weight to the .90, but packs plenty of punch!

Article Thumbnail

Displacement:1.25 cu in (20.52 cc)
Total Weight:24.69 oz (700 grams)
Bore:1.24 in (31.7 mm)
Stroke:1.02 in (26.0 mm)
Carb Type:Barrel, 2 Needle Valve
Crank Type:Dual Ball Bearing
RPM Range:1,800 - 10,000 RPM
Benchmark Prop:APC 16X6 @ 9,000 RPM
Weight of engine: (Only)21.87 oz (620 grams)
Muffler Weight:2.89 oz (80 grams)
Crankshaft Threads:M8 x 1.25 mm
Prop Range:15x7 - 17x6
Fuel:10% - 30% nitro Synthetic mix
Mounting Dimensions:152 x 60 x 126 mm
Muffler Type:Cast
Available From:Horrizon Hobby
Approximate Price: $339.99

Saito engines latest addition in their four-stroke engine family!

Model Application:3D, Precision and Sport flying! Ideal for .90 size sport aerobats all the way up to 1.20 size sport and IMAC!
Mounting Dimensions:152 x 60 x 126 mm
Internal Construction:AAC Ringed Engine
Muffler:Cast with steel header
Carburetor: Barrel, 2 Needle Valve
Glowplug: Saito SS SAIP 400S is supplied with engine. The Hangar 9 Four Cycle Super Plug (HAN3011) is the recommended replacement
Warranty: Three-year, limited


I remember learning to fly and asking my instructor about four stroke engines. His response was that they were heavy, underpowered, too hard to maintain, messy, etc. But of course I had to have one and have never regretted it.

Since then I've owned and flown almost every Saito single made, from the neat open rocker antiques, to the 1.80. All the myths about being hard to maintain, heavy and powerless might have been true years ago, but not anymore. The Saito's I own have never needed any valve adjustment after the initial break-in check. They all have performed flawlessly and just keep getting better. If properly cared for and not run lean, they won't wear out.

Saito only makes four strokes in airplane engines. They've been doing it very well for a very long time. I'm convinced they know what they're doing. If they redesigned an engine it has always been for the better. Hence the new Saito 1.25...

First Look

Box Contents

Saito's new 1.25 came in the Saito white box with their excellent fitted foam packaging. When you first open the box you notice the supplied wrench. Removing the foam top packaging reveals the engine, muffler, header and included accessories. Feeler gauges, valve adjusting wrench, and various Allen wrenches are included for maintenance. Unlike most manufacturers, Saito continues to include the tools necessary to maintain the engine.

Reminded me of opening a jewelry box!


Saito has made many improvements from the 1.20S, the engine it is intended to replace.

Some changes that help reduce the overall size and weight are:

  • a newly designed crankcase and cam cover assembly,
  • the intake tube is moved more to the left and is much more compact than the 1.20S,
  • the exhaust now exits the side instead of angled to the rear as the 1.20S,
  • the new bolt through muffler design reduces exhaust noise levels considerably.

The 1.25 is much closer in size and weight to the Saito 91S than the 1.20S. The 1.25 is almost 7 oz. lighter and much smaller in dimensions than the 1.20S. But it still retains the 2.2 horsepower rating of the 1.20S!


Engine Alone21.87 oz (620 grams)22.01 oz (624 grams)
Muffler Alone2.82 oz (80 grams)2.89 oz (82 grams)
Engine with muffler and header24.69 oz (700 grams24.9 oz (706 grams)


I was curious to see how the 1.25 compared in size to my old trusty .91S.

Saito 1.25 and .91 Size Comparisons

I had my .91 close by, so set it up on the bench next to the 1.25. The 1.25 is much closer in size with the .91S than the 1.20S it is designed to replace.

Saito 1.25, 1.20 and .91 Dimension Comparisons

Advertised specifications: FA1.25A FA1.20 Special FA.91 Special
Displacement: 1.25 cu in (20.52 cc) 1.20 cu in (19.66cc) .912 cu in (15cc)
Horse Power: 2.2 HP 2.2 HP 1.6 HP
Crankshaft thread size: 8 x 1.25 mm 8x1.25mm 7 x 1.00 mm
Bore: 1.24 in (31.7mm) 1.26 in (32mm) 1.11 in (28.2mm)
Stroke: 1.02" (26.0mm) .97" (24.8mm) .94" (
Distance Between Mounting Holes Same Side: 0.98" (25mm) 1.18" (30mm) 0.82" (21mm)
Distance Between Mounting Holes Opposite Side: 2.04" (52mm) 2.32"(59mm) 1.96"(50mm)
Distance Center of Crankcase to Drive Hub: 2.75" (70mm) 3.22" (82mm) 2.59" (66mm)
Width Between Mounting Tabs: 2.36" (60mm) 2.71" (69mm) 2.36" (60mm)
Width of Crankcase Below Mounting Tabs: 1.69" (43mm) 1.77"(45mm) 1.57"(40mm)
Length from Backplate to Drive Hub: 3.78" (96mm) 4.37"(111mm) 3.66"(93mm)
Length of back of carb to drive hub: 4.68" (119mm 5.43"(138mm) 4.56"(116mm)
Height/Bottom of Crankcase to Top of Cylinder Head: 5" (127mm) 5.19" (132mm) 4.60" (117mm)
Height/Bottom of Mounting Tabs/Top of Cylinder Head: 4.13" (105mm) 4.37" (111mm) 3.81" (97mm)
Weight: 21.87 oz (620 grams) 28 oz. (793.7 grams) 18.26 oz. (520 grams)

First Run

There is just something exciting about the first run of a new engine. I loaded up and headed to the test area. Now bare in mind it was hovering around 35 degrees. The engine was mounted to a PSP stand and a 15X6-10 Zinger prop was used for break-in.

I mounted the engine stand to the pole and filled the tank with Byron 15% fuel. After priming the engine a couple turns it was only about one revolution of the electric starter and it was running. I ran the engine for ten minutes very rich at the "less than 4000 rpm" recommended in the manual for initial break-in. By "very rich", I mean about five turns out on the high-speed needle. I also left the glow plug driver connected for the entire first 10 oz. tank. After the initial tank I noticed the compression went up considerably. I then gradually leaned it out for the remaining four 10 oz. tanks I ran through it.

The manual provided very clear break-in instructions. It stated 40 minutes break-in is adequate before mounting and flying. You should keep the engine a bit rich through the first few flight sessions.

The transition from idle to wide-open throttle was very good from the start. With a bit more running time and a 1/2-turn tweak of the low-end screw, it was perfect. There was no hesitation from idle to wide-open throttle, even after long periods of idling. I wouldn't hesitate to mount this engine and fly it at this point. It is important to keep it a bit rich and follow Saito's recommendations for the first few flights.

Second Run Session

It finally warmed up again (!) and hit 35 degrees so I headed to the engine test area to try a few different props for comparison. Here's what I found:

RPM Readings

APC 15X1089101770
Zinger 15X6-1086802130
APC 16X887602050
APC 16X1079301770
MA 16X687902010

I'm sure RPM readings will increase as the engine continues to break-in.

Sound Levels


Readings taken at app. 6 feet with an APC 16X8 prop installed.

The new style muffler really does a great job. It is very quiet for an engine this size.

Tuning Suggestion

Note: Using a tach to set this engine is highly recommended!

I've been running four stroke engines for years; yet even I found it almost impossible to set this engine accurately by ear alone. The new style muffler really does make a difference on noise levels and tone of the exhaust.




It hit about 50 degrees and the sun was peeking out occasionally. So I loaded up and headed to the field. After assembling the plane and fueling up, it was time to see what she'd do. After a couple of priming turns, I installed the glow driver and gave the prop a backwards flip. It started the first flip and settled into a nice slow idle. Using a tach, I set the top end with the 16x8 APC prop that had been installed. I ran it a touch rich at 8700 rpm. The transition from idle to wide open was excellent.

After the obligatory radio check, I taxied out and lined up in the middle of the runway. I advanced the throttle and the tail came up in 10 feet and it was airborne in less than 30. All this at around half throttle!

So I nailed it. It shot straight up to about 75 feet and died. After a rather exciting dead stick landing, I found I had inadvertently pinched the fuel line a bit inside the fuselage while installing the new engine mount and replacing the fuel tank.

My fault, not the engine's! Stupid attack on my part. All engines like fuel at full throttle.

The second take off was just like the first, except the plane just kept accelerating straight up to about 150 feet. I throttled back and then leveled off into the pattern. After a few times around the field to trim, I found I was flying straight and level at about 1/3 throttle. The engine was just quietly purring away.

I did the usual burn up the sky maneuvers: Snap rolls, loops, cuban eights, spins, hovering, inverted flight, etc. The engine just kept doing whatever I asked of it. The torque was impressive. It pulled the plane through every maneuver with authority.

I did my usual test of climbing straight up full throttle until the plane was barely visible, then idling all the way down and snapping the throttle wide open. It accelerated smoothly and passed with flying colors. But I have to admit I did raise it above idle for a second at about 100 feet. It was so quiet I couldn't hear it running! On a long landing approached I found myself doing the same. The engine is remarkably quiet!



This new Saito engine is very impressive! It performed flawlessly through all the testing. After the break-in runs and adjustment, there was absolutely no throttle hesitation. Throttle response thru the entire range from idle to wide open was excellent. This can make a big difference when "one click of throttle" needs to be "one click of throttle". It would idle very low without loading and accelerated instantly. The new weight saving, styling, power, smaller size and quieter muffler make the 1.25 and outstanding engine in its class.


The Saito 1.25 is a real winner! Being only a touch larger than the .91 and only 3.61oz. heavier is incredible. All this and retaining the 2.2 horsepower rating of the 1.20S is amazing!

It is a very well built, dependable and very strong running engine. Very easy to break in and setup using Saito’s instructions. Performing very well with all the combinations of props I ran on it. Considering the cold conditions in which I tested the engine this says a lot. I'd recommend this engine to anyone.... Everyone from beginner to the competition flyer will enjoy the performance and easy setup of this engine.

Saito's reputation of quality and dependability has always been their strong point. I have a few Saito's with well over 300 flights on them and they run as great today as when new. I'm certain that, with reasonable care, this engine will last for many years of great flying!

Thread Tools
Jun 04, 2008, 05:08 PM
Registered User

Engine thrust

Is it possible to post the static thrust aquired with the props that you used?

BTW Great review!!


Nov 12, 2008, 08:29 PM
Pro Bro # 2398
GassPasser's Avatar
saito rules !

Quick Reply

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Alert Magnum XL/ASP 1.20 FS 4-Stroke Engine Starguard Engines 19 Apr 09, 2012 02:24 PM
Sold Saito FA 91 Special w/Muffler Ringed 4-Stroke (NIB freddy warbird Aircraft - Fuel - Engines and Accessories (FS/W) 6 Jan 24, 2007 04:27 PM
For Sale Saito FA 91 Special w/Muffler Ringed 4-Stroke (NIB) freddy warbird Aircraft - Fuel - Engines and Accessories (FS/W) 0 Sep 18, 2006 12:27 AM
Sold SAITO FA-80T twin 4 stroke engine hobbylink1 Aircraft - Fuel - Engines and Accessories (FS/W) 2 Jul 17, 2006 10:08 AM
SAITO FA-72 NIB 4 stroke Engine larryfl1 Aircraft - Fuel - Airplanes (FS/W) 1 Apr 18, 2004 07:54 PM