Displacement .2124 Cu. In. (3.48cc)
Bore .650 (16.51mm)
Stroke .640 (16.26mm)
R.P.M. 2,000 - 25,000
Power Output 1.25 HP @ 25,000
Weight 9.9 oz
Propeller P-225


PLEASE READ ALL SAFETY INSTRUCTIONS! Failure to read, understand and follow these instructions could result in personal injury and/or property damage to yourself or others.

Take a few moments to familiarize yourself with the various parts of the engine. DO NOT DISASSEMBLE YOUR ENGINE! Doing so will void your warranty. No exceptions!

Improvement of former engine P/N 8906 to 8907

BRASS SLEEVE: A new feature is a heavier wall brass sleeve made from a harder and stronger brass alloy.  The combination minimizes distortion during machining as well as at running temperatures.  New machines and a new machining process on the sleeve bore guarantees a truer and rounder surface.

NEW ADVANCED TECHNOLOGY BALL BEARINGS: A superior and durable ball bearing has evolved from many years of R/C car racing.  Hard running demands that the bearing withstand 30,000 plus R.P.M. without shedding the ball retainers, withstand high temperatures without seizing, and last... almost forever.  To meet these demands, K&B has developed and produced its own version of the super bearing.  We have equipped your new outboard engine with these bearings.

CRANKCASE: Besides the extra web braces previously added to the exhaust flange, the crankcase now sports beefed up mounting lugs in the shape of web braces.   It should be noted here, that the crankcase has been bored out larger to accept the heavier well sleeve.  Therefore, the new sleeves and crankcase are not interchangeable with the older version engines.  All other parts are interchangeable.

NEW CONNECTING ROD: In our continued efforts to produce a better product for you, modeler, we have equipped your engine with a fully machined con-rod made from high tensile strength aluminum stock.  They are also now bushed at both ends, and profiled to add strength.

NEW CRANKSHAFT: Our 3.5cc outboard engine is being run at between 29 000 and 30,000 RPM.  As a result, reports of crankshaft failure surfaced. Therefore, in our effort to make the engine as (???) proof as possible we have increased the crankshaft diameter from 12ram to 13ram.

THREADED PROPELLER SHAFT ASSEMBLY: The prop shaft assembly and mating part of the lower end casting are threaded (note: left hand thread).  A secure and long wearing assembly is the result.  The drive cable can now be inspected without removing the powerhead.   Simply unscrew the prop assembly and pull out the cable.

This outboard still boasts another feature, the prop shaft bushings are of new material that requires nothing but water as a lubricant.   Extended tests have shown that they will last for hours of running with very little wear.


NEW CLEANING AND LUBRICATING FEATURES: K&B has added two new features to enhance operating condition and longevity.  A cleaning hole has been added to the front plate to aid in cleaning the front or top bearing.  Simply place an aerosol can of Liquid Wrench (or similar product) up to the hole and "back" flush the bearing.  Continue to flush the bearing until you see fresh cleaner come out under the flywheel.  The bearing may also be oiled, in the same manner.

A lubricating hole for the flex shaft has been added to the lower unit.  It is recommended that each time, before you run the unit, you lubricate the cable with a mixture of 50% STP and 50% 20-50 weight oil.  K&B still recommends that you continue to remove, inspect, and re-lube the flex cable (using Lube P/N 8449) on a continued basis.

MAINTENANCE: We recommend after each days running, that you check each bolt and screw for tightness.

CAUTION: For maximum life of propeller shaft bushing do not operate engine out of the water for a period of longer than thirty (30) to forty-five (45) seconds.

GLOW PLUGS: This engine is designed to use the long reach glow plug (K&B P/N 7311).

MARINE PROPELLERS: Propellers are naturally an important factor.  Most propellers that are available on the market need balancing and "cleaning up".   Unbalanced props cause cracks on boat not to mention robbing your engine of horsepower and your boat of performance.  So, balancing the prop is very important.   You can buy a fixture for checking balance or you can make your own.  To make your own, mount two single edge razor blades, sharp edges up, parallel to each other and about 1 1/2 inches apart on a piece of aluminum "U" channel (or make your own "U' channel out of wood).  Make sure the sharp edges are level with each other and with the table.  Slip a length of 3/16 diameter shafting (drill blanks are best) through the prop.  Place the shaft across the razor blades with the prop in between.   The heavy side of the prop will roll to the bottom.  File on this area until the prop is balanced.  Do not file on the concave part of the prop.

Cleaning up the propeller means to sharpen the leading edges of the blades and generally sanding, smoothing, and polishing the entire prop.

FUEL: We recommend using K&B 1000+ (25% Nitro) or K&B Speed Fuel (50% Nitro).  Fuel must have a minimum of 18% oil by volume.


An "ABC" type engine (Aluminum, Brass, Chrome) does not require prolonged break in periods.  However, we do recommend that you run the engine at a slightly rich needle valve setting for the first two runs.   These runs should be made with the engine installed on the boat and running in the water for periods of not less than five (5) minutes each.  Typically, an engine will be ready for continuous full throttle and a leaner needle valve setting after ten (10) to fifteen (15) minutes of running.

CAUTION: If the engine is run at a lean needle valve setting during the break in period, the following may result:

1.    Piston and sleeve will overheat and score.

2.    The connecting rod, crankshaft and wrist pin will overheat from lack of lubricant and seize, causing the lower con-rod bushing to spin in the con-rod, or in extreme cases, the bottom of the con-rod will break, causing damage to the crankcase, piston and sleeve.
3.    The crankshaft may seize inside the front plate and fracture.


The outboard is mounted directly to the transom of your boat. If you are using an adjustable motor mount, the outboard mounts to the motor mount and it in turn mounts to the transom.

POSITIONING THE OUTBOARD IN RELATION TO THE BOTTOM OF THE BOAT: First of all, you must make sure that the transom is square to the bottom or riding surfaces of your boat hull.  A 3 to 4 degree variation is okay.   Any more than that will require a tapered wooden, aluminum, or epoxy putty shim glued to the stern.


  1. TUNNEL HULL:  A good start using the prop provided, is to position the outboard so that the lowest part of the boat are even with the top of the propeller bushing housing. (The streamline threaded part of the lower end casting in front of the propeller).
  2. FLAT or V BOTTOM HULL:   The starting position for a flat bottom or shallow V bottom hull is the same as the tunnel hull.  On V bottom hulls with a V greater than 14 degrees, lower the engine approx. 1/8 inch.  These settings are approximate and will vary from hull to hull.
  3. HYDRO HULL:  The riding attitude varies between hulls, and since we do not know which hull you will use, we can only suggest that you follow the manufacturer's suggestions.  Now that you have decided where to mount your outboard drill the holes for your motor mount, we suggest that you allow equal up or down motor mount adjustment
Tests have proven that the cable drive is far superior to the gear drive.  Maintenance is cut down to a minimum.  However, we ask that you occasionally check and lubricate the flex cable.  Check for excess wear and fraying.  Do not rotate the engine by flipping the propeller in a counter-clockwise direction.  Fraying and unwinding may occur.  We recommend a good silicone base lubricant such as K&B marine grease (P/N 8449) for your outboard as well as other drive units.

INFORMATION: The deeper you run the propeller in the water, the smaller the diameter and or pitch must be.  Reason: There is more water surrounding the prop thus more bite and more load on the engine.  Do not overload the engine, as the engine is more efficient at higher RPM's (18,000 to 22,000), it will be more dependable if you keep it within that range.  If you want to use a bigger prop, raise the engine.  This allows the prop blades to surface out of the water.  There is less water surrounding the prop, thus, less load on the engine.


Please note that the lower unit of your outboard engine has a pressure tap fitting.  Although the use of pressure is not an absolute necessity, we highly recommend it as it makes for a smoother and more even run from a full to empty tank of fuel.  You must connect a length of fuel tubing between tile pressure fitting and the air vent tube on the tank.

NEEDLE VALVE ADJUSTMENT: Assemble the needle valve onto tile carburetor and turn it clockwise to completely close it.  Turn until it won't go any further but do not force it. Then turn it counter-clockwise 4 to 4 1/2 turns, if you are running rear sea level, 3 1/2 to 4 turns at higher altitudes.  As these are only starting settings, you might have to re-adjust the needle valve to make it the correct setting for your area.   Once you have arrived at a setting, you can lock the needle valve in place as the carburetor has a built in collet lock.  Turn the black acorn nut clockwise to lock the needle valve in place, counter-clockwise to loosen.  It takes a 1/4 inch wrench.   Only tighten it enough so that the needle valve cannot be moved. Do not force it.

IDLE ADJUSTMENT: Your carburetor has an engine idle adjustment.  It's the screw on top of the carburetor with the spring under it.  If you turn it counter-clockwise, the engine will idle slower.  If you turn it clockwise, the engine will idle faster.   By looking into the carburetor venturi, you will note that the hole opens and closes as you actuate the carburetor arm back and forth.  Notice the notch on the one side of the barrel (the moving part with the hole in it).  Turn the idle adjustment screw counter-clockwise until the notch disappears.  This will shut the engine off completely.  With the carburetor linkage installed and the transnutter throttle and trim set at completely closed position, (make sure that the carburetor idle is set so that the notch in tile barrel is not visible), then with the transmitter trim, open the carburetor so that the notch is now visible for 1/16 of an inch.  This is the starting position.



As mentioned before, the engine runs in a clockwise rotation.   Make certain that your starter motor is running in the same direction.  With the tank full of fuel and the glow plug battery leads off, fully open the carburetor and with your finger covering the carburetor venturi, spin the engine with the starter for about a two second burst.  This primes the engine.  Now close the carburetor to the starting position.  Connect tile GLOW battery and spin the engine again.   The engine should fire up and run.  We recommend that you start your engine close to the water so that you will not have too far to walk with the engine running with no water circulating through the cylinder head it is also advised that you keep the engine at a slow or not greater than a slightly fast idle until you get into the water, as over revving plus overheating can damage your engine.
We recommend that you use a fuel filter in your fuel system.   Install the fuel filter on the fuel pickup tubing between the tank and carburetor.  It will keep foreign matter from going into the carburetor to create clogging.  However, the filter also can clog up.  Therefore, should it clog, remove the filter from the fuel line and clean it as per the manufacturer's instructions.   If you do not have a fuel filter in your system, there is a chance that foreign matter will find its way into the carburetor causing your engine to run at a very lean setting, no matter how much you open the needle valve.  The particles will wedge themselves in between the needle valve point and the fuel outlet tube (spray bar).   The best way to remove them is by removing the complete needle valve, lock nut and all.  Remove it by unscrewing the brass nut just next to the black lock acorn nut.   This opens up the fuel chamber inside the carburetor, then blow into this chamber.   This will clear out the spray bar.  Replace the assembly and snug up the brass nut.  Check your fuel and pressure lines frequently for holes or cracks that could also cause the engine to run lean.


We realize that not everybody will run their outboard in saltwater.   Those of you that will, however, should heed the following information:

It is a must to take a can of spray lube with you when saltwater racing.  Before and after each run, spray all metal hardware on your boat (this includes the engine) with spray lube.  At the end of the day's running, remove the glow plug and by spinning the engine through with the starter, flush at least two ounces of fuel through the engine by holding your finger over the venturi.  Then, pour a good amount of spray lube oil into the venturi and spin the engine again for a short spurt.  Flush the rest of the outboard and boat with lots of fresh water.   Spray lube all moving parts, and threads on screws. Also flush the bearings and lower unit as described in the beginning of this manual.


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