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Only Saito could put 1.25 cubic inches of power into a 1.00-size case!


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FA-125A AAC with Muffler: AG
  • Overview
  • Specs
  • Reviews
  • Parts & Accessories
  • Manuals & Support

Key Features

  • Less weight but more thrust
  • 10 ounces lighter than the FA-120
  • Turns an APC 16x6 at 9,000 rpm
  • 13mm Muffler threads

Needed To Complete

Propeller:  16x6


Only Saito could put 1.25 cubic inches of power into a 1.00-size case. Not only is the FA-125 lighter and more powerful than the FA-120 it replaces, its unique size allows modelers to apply its awesome power to a wide variety of airplane sizes. It will work with anything from .90-size sport aerobats all the way up to 1.20-size sport and IMAC planes. As with most Saito engines, the FA-125A is available in a stunning Golden Knight version with a gloss black finish and gold-plated valve covers.

With 10 fewer ounces and .05 more cubic inches than the FA-120 it replaces, the FA-125A gives new meaning to the term “escape velocity.” Just bolt one to the nose of Hangar 9’s ShowTime™ 90 and you’ll see what we mean.

Benchmark Prop: APC 16X6 @ 9000 rpm
Bore: 1.24 in (31.7mm)
Carb Type: 2 Needle
Crankshaft Threads: M8 x 1.25mm
Crankshaft Type: Dual Ball Bearing
Cylinder Type: AAC
Cylinders: Single
Displacement: 1.25 cu. in. (20.52 cc)
Engine (Only) Weight: 21.87 oz (620 g)
Mounting Dimensions: 119 x 60 x 127mm
Muffler Type: Cast
Prop Range: 15x7 - 17x6
RPM Range: 1800 - 10000 rpm
Recommended Fuel: Glow
Stroke: 1.02 in (26.0mm)
Total Weight: 24.69 oz (700 g)

Parts Listing

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$10.69  $10.16
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Pushrod: VV SAI200TI39
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Optional Accessories

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Product Support Tips

The New Saito 125a and Saito 125aGK

Well, here we go again! With this new Saito engine, it isn’t a question of whether it makes more power than the FA-100 that it came from, but rather how can it be 10 ounces lighter than the current FA-120 (large case) engine that it has to live up to? Side by side, it looks like it just can’t be!

It’s true! With the APC 16x6 prop, the Saito FA-125a is singing at 9000 rpm using standard 15% nitro content fuel. The initial flight-testing was performed in the tried and true, do it all, Hangar 9 Ultra Stick Lite. This model has been powered by everything from an Evolution 100 glow engine to Saito 180, and even 220a engines as well as a couple of Evolution Gas 26cc engines along the way. With most of the larger engines, the model ends up nose heavy and requires additional weight in the tail to balance properly. With the FA-125a, the balance is finally back where it belongs!

But first, some background. The Saito company must have roots in the American auto Hot Rod enthusiasts’ formula of boring and stroking engines to increase displacement. Existing engines like the FA-50 became the FA-56, the FA-72 became the FA-82 and the FA-120 eventually was increased all the way to an FA-180. All have been successful and so the same formula was applied to the FA-100 resulting in a displacement of 1.25 cubic inches. But the surprise comes when it is compared to the current FA-120, which has served modelers very well for a number of years. The FA-125a is much smaller externally and the difference in weight of 10 ounces, roughly one-third less, gives a wonderful power-to-weight ratio! Prop speed and size is basically the same as the

It is recommended that you follow the break-in procedure in the manual before flying your model with the FA-125a for the first time. Start-up using the tried and true method used on all the Saito 4-stroke engines results in first flip starts every time.

A)  Fill the fuel tank

B) Make sure the fuel feed and muffler pressure lines are hooked up correctly

C) Put your finger over the exhaust outlet, open the carb, turn the prop through two compression strokes, close the carb to idle position

D) Hook up the glow power and flip the prop backwards against the compression.

The Saito will fire off first try.

Now at the flying field this thing is impressive! Keep the needle a bit rich for a few flights to assure that you do not overheat the engine.

Even with the slightly rich settings, the FA-125a just “jerks” the Ultra Stick off the ground when you punch full throttle; pull back on the elevator and it just keeps going! Ok, so it climbs—how about an extended spin cycle back to low altitude at idle, 17, 18, 19, 20 turns—yikes, pull out! Engine is still idling at 1800 all the way to the bottom and recovers to full throttle with no roughness or missing at all. Right away it becomes apparent that the FA-125a has response to throttle settings we have all been looking for- very linear and each click off of idle results in a small rpm change. With this kind of throttle response the model responds sooo nicely in hover and harrier maneuvers or while doing tail wheel only touch and goes.

One other aspect that keeps everyone happy, but is not usually associated with performance testing, is the level of sound that this engine does not generate! We noticed on the first flight that it was quiet. You just can’t hear the engine run when other models are in the air. Everyone watching has the same observation, “You can’t hear it run in the air.” It is remarkable, and I am sure this will also be a welcome aspect at the local R/C flying field.

Fuel consumption is very reasonable and the standard tank in the Ultra Stick might be judged to be larger than necessary, but flying this combination is enough fun that extended flights become the norm. And of course, all of your friends want a bit of time on the sticks as well, so a little extra fuel can’t hurt.

This Saito seems to be a real R/C flyer’s dream; it will power just about any kind of model and keeps on ticking, ready for more. Easy to mount, easy to run, easy (and reliable) to fly with huge power! If you purchase this Saito you just might not have time for some of the other engines that get left at home! Here is one with lots of built-in FUN.


Warranty Period:

What this Warranty Covers:
Horizon Hobby, Inc., (Horizon) warrants to the original purchaser that the product purchased (the "Product") will be free from defects in materials and workmanship for a period of 3 years from the date of purchase.


Limited Warranty:

What is Not Covered:
This warranty is not transferable and does not cover (i) cosmetic damage, (ii) damage due to acts of God, accident, misuse, abuse, negligence, commercial use, or due to improper use, installation, operation or maintenance, (iii) modification of or to any part of the Product, (iv) attempted service by anyone other than a Horizon Hobby authorized service center, or (v) Products not purchased from an authorized Horizon dealer.


Purchaser’s Remedy:
Horizon’s sole obligation and purchaser’s sole and exclusive remedy shall be that Horizon will, at its option, either (i) service, or (ii) replace, any Product determined by Horizon to be defective. Horizon reserves the right to inspect any and all Product(s) involved in a warranty claim. Service or replacement decisions are at the sole discretion of Horizon. Proof of purchase is required for all warranty claims. SERVICE OR REPLACEMENT AS PROVIDED UNDER THIS WARRANTY IS THE PURCHASER’S SOLE AND EXCLUSIVE REMEDY.

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HORIZON SHALL NOT BE LIABLE FOR SPECIAL, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES, LOSS OF PROFITS OR PRODUCTION OR COMMERCIAL LOSS IN ANY WAY, REGARDLESS OF WHETHER SUCH CLAIM IS BASED IN CONTRACT, WARRANTY, TORT, NEGLIGENCE, STRICT LIABILITY OR ANY OTHER THEORY OF LIABILITY, EVEN IF HORIZON HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Further, in no event shall the liability of Horizon exceed the individual price of the Product on which liability is asserted. As Horizon has no control over use, setup, final assembly, modification or misuse, no liability shall be assumed nor accepted for any resulting damage or injury. By the act of use, setup or assembly, the user accepts all resulting liability. If you as the purchaser or user are not prepared to accept the liability associated with the use of the Product, purchaser is advised to return the Product immediately in new and unused condition to the place of purchase.

These terms are governed by Illinois law (without regard to conflict of law principals). This warranty gives you specific legal rights, and you may also have other rights which vary from state to state. Horizon reserves the right to change or modify this warranty at any time without notice.


Questions, Assistance, and Services:
Your local hobby store and/or place of purchase cannot provide warranty support or service. Once assembly, setup or use of the Product has been started, you must contact your local distributor or Horizon directly. This will enable Horizon to better answer your questions and service you in the event that you may need any assistance. For questions or assistance, please
fill out our inquiry form, or call 877.504.0233 toll free to speak to a Product Support representative. You may also find information on our website at  

Inspection or Services:
If this Product needs to be inspected or serviced, please use the Horizon Online Service Request submission process found on our website or call Horizon to obtain a Return Merchandise Authorization (RMA) number. Pack the Product securely using a shipping carton. Please note that original boxes may be included, but are not designed to withstand the rigors of shipping without additional protection. Ship via a carrier that provides tracking and insurance for lost or damaged parcels, as Horizon is not responsible for merchandise until it arrives and is accepted at our facility. An Online Service Request is available at under the Support tab. If you do not have internet access, please contact Horizon Product Support to obtain a RMA number along with instructions for submitting your product for service. When calling Horizon, you will be asked to provide your complete name, street address, email address and phone number where you can be reached during business hours. When sending product into Horizon, please include your RMA number, a list of the included items, and a brief summary of the problem. A copy of your original sales receipt must be included for warranty consideration. Be sure your name, address, and RMA number are clearly written on the outside of the shipping carton.

NOTICE: Do not ship LiPo batteries to Horizon. If you have any issue with a LiPo battery, please contact the appropriate Horizon Product Support office.

Warranty Requirements:
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Non-Warranty Service:
Should your service not be covered by warranty service will be completed and payment will be required without notification or estimate of the expense unless the expense exceeds 50% of the retail purchase cost. By submitting the item for service you are agreeing to payment of the service without notification. Service estimates are available upon request. You must include this request with your item submitted for service. Non-warranty service estimates will be billed a minimum of ½ hour of labor. In addition you will be billed for return freight. Horizon accepts money orders and cashiers checks, as well as Visa, MasterCard, American Express, and Discover cards. By submitting any item to Horizon for service, you are agreeing to Horizon’s Terms and Conditions found on our website

United States:
Electronics and engines requiring inspection or repair should be shipped to the following address:

Horizon Service Center
4105 Fieldstone Road
Champaign, Illinois 61822

All other Products requiring warranty inspection or repair should be shipped to the following address:

Horizon Product Support
2904 Research Road
Champaign, Illinois 61822

Please call 877-504-0233 or fill out our inquiry form with any questions or concerns regarding this product or warranty.

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