Moki2008 

User Guide for MOKI Glow Engines 

...is this a MARK or a MOKI? 

The powerful MARK engines are manufactured in Hungary by MOKI Motor – previously known as 

MOKI. Throughout the world, the brand name MOKI has become the synonym of performance and 

dependability amongst demanding modelers – for competitions just as much as for the plain fun of the 

hobby. As famous as the brand name MOKI has become, unfortunately some ownership issues around 

the copyright of the name have occurred. For this reason MRC has chosen to re-brand the engines 

under the name MARK. So – regardless whether you own a MARK or a MOKI – your engine has been 

developed by some of the most experiences model engine experts and has been assembled by hand in 

Hungary to live up to your highest expectations. 

History 

MOKI/M/ARK engines have been manufactured since more than fifty years. The Hungarian 

Department of Defense founded MOKI in 1957 with the charter of developing and manufacturing 

engines for the use in airplane models as well as for military purposes. This heritage can still be found 

in the name MOKI: the acronym stands for “Modell Kisérleti Intézet”, which in Hungarian means 

“Institute for Experimental Modeling”. Until 2008 the factory has resided at the original location at the 

airport of Budaörs, a few miles west to the center of Budapest. 

Until 1989, the entire production capacity was reserved for use by the competition modelers 

(airplanes, cars and boats) in Hungary and the army. The engines became famous due to the 

successes of Hungarian modelers, but there was no commercial pressure on production. This unique 

situation allowed the development team to focus on performance and dependability – the elements 

most important for success. 

Hungarian modelers have gathered about two hundred European and World Championship titles, and 

a long list of world records. Many modelers participated at races, while at the same time working for 

MOKI. One famous example is Mr. Gyula Krizsma – World Champion in high-speed control-line flight in 

1962 – and the engineer responsible for the development of MOKI’s two-stroke engines. Until today, 

his designs form the basis of the successful line-up of MARK engines. 

The experience grown in more than fifty years of manufacturing high-performance model engines has 

survived all economical and political changes brought about by the fall of the iron curtain in 1989. Now 

a company in private ownership, the team is concentrating on fulfilling the demands of modelers 

world-wide for dependable, high-performance engines. 

Our motto is “Competition quality for the demanding modeler” . Stringent, industry-level quality 

assurance processes and modern CAD and CNC equipment combined with half a century’s worth of 

experience are an excellent base to provide you with powerful, long lasting engines of classical design. 

Numerous tests in magazines and an impressive track record of international prizes are the 

testimonials to our claim. We strive to preserve these values for the future. 
Moki2008 

Technical Data 

Please note that the performance and RPM figures depend strongly from external factors such as 

barometric pressure / altitude, fuel and propeller used etc. The figures given above relate to typical

measurements done at the factory. 

Dimensions 

Displacement

cubic inches

Displacement

cubic cm Bore mm Stroke mm Max. R.P.M. Performance kW / HP Weight

M 51 0.51 8.37 22.5 21 12,500 0.65 / 0.9 390g / 13.76 oz

M 61 0.61 9.97 23 24 17,500 1.62 / 2.2 495g / 17.46 oz

M 135 

M140 1.38 22.6 31.5 29 13,000 2.86 / 3.9 855g / 30.16 oz

M 180 1.82 29.8 35 31 12,000 3.0 / 4.1 1170g / 41.27 

oz 

M 210 2.11 34.6 36 34 10,000 3.3 / 4.5 1275g / 44.97 

oz 

M 360 2 x 1.82 2 x 29.8 35 31 11,000 5.7 / 7.8 2270g / 80.07 

oz 
Moki2008 

(All dimensions below in millimeters) 

 A B C D E F G H I J K L

M 51 45 26 85 72 39 8 36 52 - - 39 28 

M 61 51 28 93 83 44 9 42 60 - - 45,5 28 

M 135 

M 140 60 35 112 102 57 9 51 71 85 22,5 54 40 

M 180 68 36 126 112 62 10 56 80 100 32 56 34 

M 210 70 38 127 118 64 11 60 82 100 30 61 34 

M 360 68 36 195 112 62 - 56 80 - - 56 34 

Precautions 

Throughout this User Guide we assume, that you have already gathered experiences in operating a 

glow engine, and that this is not the first engine you operate. Should this indeed be your first 

experience with a glow engine, we strongly recommend that you seek professional advice from a more 

experienced modeler, for example in your club, or from the reseller who has sold this engine to you. 

The power and performance of MOKI engines can be very dangerous if the engine is not handled with 

the appropriate precaution, serious injuries or even fatalities can be the result if insufficient care is 

taken. Please read the entire manual carefully before attempting to start the engine. 

• The engine most be mounted firmly to a test bench or into a model, the model or the test 

bench must be fixed appropriately. 

• A suitable, balanced and undamaged propeller of appropriate size must be used. 

• The original propeller nut or another suitable propeller nut must be used and tightened firmly. 

Using spinners with thick back-plates and/or propellers with an unusually thick hub can lead to 

insufficient grip of the propeller nut. In this case a special adaptor must be used to ensure 

that the propeller and the spinner are held in place firmly. Please contact us or a third-party, 

specialized company (e.g. TruTurn) to acquire a suitable adaptor. 

• Carefully check the tightness of the propeller nut on a regular basis. Some materials (like 

wood) have a tendency to be compressible by the propeller nut, leading to a loose propeller 

nut. 

Breaking-In a New Engine 

Breaking-in (sometimes also called running-in) your new engine carefully is an important measure to 

ensure longevity as well as high performance. You can either mount the engine to a test stand, or 

install it into your model. It is important that the engine gets sufficient cooling and that the propeller 

is not oversized. 

Please use a quality fuel with at least 20% oil content and no nitro methane for the first hours of 

operation. Using a high quality castor oil in this phase makes sense and shortens the required time 

until the engine is run-in. If you prefer not to use castor due to its unpleasant side effects (like sticky 

exhaust residues, intensive odor), you can also use synthetic oil. Please consider that due to the 

better lubrication with synthetic oils the time required until the engine reaches its peak performance

may take a bit longer. In any case, make sure you use first-class quality fuel or fuel components. 
Moki2008 

At the beginning, the carburetor’s main needle should be set in such a way that the engine does not 

rev higher than 5-6,000 rpm at full throttle. Run the engine in short intervals of about five minutes,

which you can subsequently increase by a minute after each run until you reach ten minutes. Allow 

the engine to cool out entirely between two runs (this is very important, as the temperature changes 

contribute significantly to the process). After the first few intervals you can start leaning the main

needle click by click. NOTE: If the engine revs start decreasing (“sagging”), immediately open the 

main needle several clicks, as sagging revs at a constant throttle setting are a sure indicator for 

overheating. 

After the first few intervals you should also try changing revs with the throttle – as soon as the engine 

safely holds an idle without a connected glow driver it’s time to get the model in the air. Flying is a 

much better way of running-in the engine, as the cooling is much better, the static load on the engine

is lower and the operation at alternating revs is good for the engine. Avoid long full-throttle phases, 

and change revs as often as you can. 

You can tell that the engine is broken in as soon as the engine holds a peak rev without sagging, and 

you can dial-in a low, steady idle. Now you can also reduce the oil content in your fuel to about 17% 

of a high-quality synthetic oil (if you use castor, please do not reduce the oil content, stay at 20%). A 

very important notice: Many times we have heard that “an experienced colleague”, “the club’s engine 

guru” or “the guys at the field” have said something like “My engine of the brand xyz runs perfectly 

with x% oil (x being a very low figure like 8 or 12)”. Please, DO NOT LISTEN TO SUCH 

INCOMPETENT STATEMENTS. First of all, we believe that we, as designers and manufacturers of 

our fine engines, do know best what the engine has been designed for. Secondly, the required amount 

of oil differs due to several facts and depends very much on the design specifications. A highperformance engine like ours has much tighter fittings than some of the competitor’s engines – this is

true for the connecting rod bushings as well as for the hand-selected cylinder/piston pair. The small 

tolerances used in these parts are an important contributor to the reliability and dependability of our 

engines. Low oil content not only can cause lubrication problems, but it also increases the engine 

temperature (thus increasing wear) and provides no reserves should you experience a lean run due to 

e.g. wrong carb setting, the pressure line on the muffler failing etc.. Please note, that our warranty

does not cover any damages to the connection rod, piston or cylinder due to overheating or the use of 

insufficient or bad quality oil. 

Installing the Engine 

The engine can be mounted to your model either via the mounting lugs or with the help of the coneshaped engine mount available as an accessory for some of our engines. This engine mount replaces 

the standard rear cover of the engine and can be attached directly to our model’s firewall. Make sure 

to replace the standard rear cover mounting screws with the longer ones that come with the engine 

mount. 

The Mark M360 In-Line Twin should always be mounted with the special engine mount available for 

this engine. Although the cone-shaped engine mount of the M180 mechanically also fits the M360, it 

should not be used as the engine’s length and the sheer power it produces cannot be mounted 

securely using the cone. 

Please do take the engine’s power and high torque into consideration when mounting it to your model, 

especially if you use any rubber elements. Be careful as some types of rubber disintegrate over time 

under the influence of oil and fuel. Always use a locking compound on the screws used for engine 

mounting. 

Make sure that there is sufficient air flow to cool the engine. The air stream should flow directly to the 

cylinder and cylinder head. If you use any cowl, make sure that the air outlet has at least twice the 

opening area of the air inlet – hot air expands and thus needs a larger exit to ensure a proper flow. 

When installing the M360 In-line Twin particular care should be taken to ensure that the rear cylinder

is appropriately cooled. 
Moki2008 

The following symptoms are clear indicators of overheating: 

• Loss of power / sagging revs at full throttle despite correct carburetor settings 

• Frequently fouled glow plugs (you can diagnose overheating before the plug fails – the coil 

should be shiny, and the plug body should not be discolored. If you see any discoloration, or 

the coil is not shiny, then the engine has been exposed to overheating). 

• Loosening cylinder head screws – this is a severe alarm signal and a clear indicator of 

intensive overheating! 

If you observe any of these symptoms, take action and ensure that your engine gets adequate 

cooling. This will ensure a long life and reliable high performance. 

Fuel Tank and Fuel Lines 

The fuel tank should be installed in the model in such way, that the centerline of the tank is on the 

same height as the engine’s needle valve. This ensures a constant and steady flow of fuel. Use foam 

to protect the tank against vibration, and use muffler pressure to pressurize the tank. Please use fuel 

tubing (including the tank’s plumbing, any filters or filling valves) of an adequate diameter, to ensure 

that there is sufficient fuel flow under all conditions. If you notice, that you can turn the needle valve 

counterclockwise without any effect on the engine’s r.p.m., you have probably installed insufficiently

sized fuel tubing. 

The Carburetor 

 The carburetor used on MOKI engines uses a needle valve to regulate the engine’s high speed fuel 

mixture. The fuel mixture from idle to mid-range is controlled by an idle disk. 

On the same side as the needle valve you can find a knurled disk. This disk has a little groove on the 

top, and a “+” and “-“ symbol are punched on its face. By turning the disk into the “+”-direction, the

fuel mixture for idle and mid-range is made richer (so more fuel can flow), turning the disk into the “-

“-direction provides a leaner mixture. Please change the setting of the disk only in very small steps!

The factory setting of the disk is with the groove exactly on top center. For the time being, do not 

change the factory setting! 

The main needle is delivered separately in the box. Carefully insert the needle into the valve, and 

gently screw it in all the way. Do not apply any force. After the needle has been completely screwed 

in, turn the needle valve out three full revolutions. With this base setting – main needle valve out 

three revolutions and idle disk centered – the engine should start and run in any case. Only minor 

changes to the main needle and the idle disk should be required to obtain the maximum power and a 

reliable idle. Please note that the ideal carburetor settings depend on the viscosity of the fuel, the

barometric air pressure at your flying site (altitude), relative humidity and temperature of the air –

just to mention a few factors. Please find below how to find the optimum settings. 

Starting the Engine 

MOKI engines are really easy to start, and can easily be hand started – provided you have the 

required practice. Always use a stick when starting the engine by hand! Please keep in mind that highperformance glow engines like the MOKI engines can cause serious injuries if handled improperly. For 

this reason, we strongly recommend to use an electric starter. If you prefer starting the engine by 

hand, ALWAYS USE A STICK and protect your hands with heavy leather gloves. 

Optimizing the Carburetor Settings 

This chapter explains how to get the best performance once the engine has been run-in. Begin by 

starting the engine, and allow the engine to warm-up, if necessary, with connected glow power. After 
Moki2008 

a few minutes, remove the glow power, and slowly advance the throttle to full power (make sure that 

the model is well secured, ideally a helper should hold it). Adjust the main needle valve so that the 

engine reaches its peak rpm, then open the needle valve (counterclockwise) until the rpm drops by 

about 500 rpm. Always keep the engine on the “rich” side when flying! Check that the engine runs 

stable also with the model’s nose held straight up. A slight increase in revs is OK, but should you need 

to open the needle valve so much, that no clean running is possible once the model returns into a 

horizontal attitude, then probably the tank is installed incorrectly (too far from the engine, or too 

high/too low in relation to the carburetor). Once you are satisfied with the engine’s setting at full 

power, reduce the throttle to a low idle and let the engine run at idle for a few minutes. Check if the 

engine’s acceleration is quick and without any sputtering or hesitation. If the acceleration is not 

satisfactory, return the engine to idle, and briefly pinch the fuel line with your fingers. If the engine 

revs up, stop the engine and turn the idle disk a very small amount towards the “-“ sign, if the engine 

suddenly stops without first revving up, turn the idle disk a small amount towards the “+”. After 

changing the idle disk’s setting, check the main needle’s setting at full throttle as described above.

Repeat the process until you are satisfied. 

Shutting off the Engine 

All glow engines produce a fair amount of exhaust residue containing acids and organic solvents. As 

long as the engine is hot, these corrosive residues will evaporate and exit through the exhaust. 

However, if you let the engine run at idle revs for a while, the engine will cool down and the residue

will condensate and be trapped in the engine’s exhaust system as well as the crank case. The colder 

the outside temperature, the larger the exhaust, the stronger this effect! It is therefore very important 

to ensure, that after the last flight of the day, the engine is shut off at full temperature. It is good 

practice to allow the engine to run at full power for one or two minutes, before shutting the engine off 

by closing off or pinching the fuel line (do not stop it by covering the carb inlet, this will draw 

additional fuel in the crank case and will contribute to the build-up of corrosive residues). Make sure 

that the exhaust is drained from any residues, and store the model with the engine pointing upwards 

– this prevents any residues to flow back into the engine. Please note that damages caused by 

corrosion are not covered by the warranty! 

Selecting the Best Suitable Propeller 

The choice of a suitable propeller depends on many factors, such as the characteristics of your model,

your style of flying, the fuel you use, the type of exhaust system, the atmospheric conditions etc. 

Please note, that the same nominal size of propeller can deliver quite different results from brand to

brand. In the case of wooden propellers even two propellers of the identical size and the same brand 

can deliver very different results. For this reason, the table below can only serve as a rough indication 

of typical propeller sizes – the best is to try several prop sizes until you find your favorite. The first 

number denotes the propeller’s diameter; the second number represents the pitch (all measurements 

in inches). Please make sure not to exceed the maximum rev number in the table to prevent the 

engine from damages. Please note that the rev figures measured on a static model on the ground will 

be considerably lower than the peak rpm reached in flight – so keep a safety margin of at least 1000 

rpm. MOKI engines are designed to deliver a very high torque; therefore you can use relative larger 

diameter props at lower revs. Not only will this render a better efficiency, it also contributes to lower 

noise emissions. 

Please observe the following guidelines: 

• Only use undamaged propellers 

• Don’t use propellers with an unknown history 

• Heavy propellers (carbon fiber, composites) have a larger “flywheel”-effect and allow for a 

lower idle while wooden propellers result in a brisker acceleration of the engine 

• Any discoloring on the surface of a plastic propeller is an indication of structural damage – do 

not use any props with such marks, discard them! 

• Propellers have to be balanced carefully 
Moki2008 

• Take utmost care when enlarging the hole in the prop hub – use a drill press, or ream it by 

hand 

• If you use a spinner make sure that the spinner is balanced and use the appropriate fastening 

nut. Please consult your MOKI dealer for special propeller nuts with an integrated thread for a 

spinner mounting screw. These are available both from MARK as well as manufacturers of 

spinners. 

Displacement

cm3 Propeller size (2 blades) Max. R.P.M.

M 51 8,37 10 x 9 – 12 x 6 12,500 

M 61 9,97 10 x 12 – 12 x 10 17,500 

M 135 

M 140

22,6 14 x 12 – 18 x 6 13,000 

M 180 29,8 17 x 12 – 19 x 8 12,000 

M 210 34,6 18 x 12 – 20 x 10 10,000 

M 360 2 x 29,82 22 x 10 – 24 x 8 11,000 

Exhaust System 

Suitable exhaust systems are available from many brands. Consult your MOKI engine dealer for the 

ones available in your market. If you plan to use a tuned pipe system, please make sure that you use 

the adequate length of header pipe. The longer the pipe is, the lower the RPM when the resonator 

effect kicks in. If the pipe is too short, the engine will have a tendency of overheating. Another 

important factor is the muffler’s volume: if the muffler is too small, too much unburned exhaust 

gasses will flow back from the muffler into the engine. The typical symptom is that when cutting the 

throttle, the engine will not fall back to idle quickly, but will continue to run at a medium RPM level for 

several seconds. If you experience this symptom, you can try adjusting the mid-range of the carb 

slightly leaner, or increase the area of the muffler’s exit pipe. If these measures don’t help you will 

have to switch to a muffler with a larger volume. 

Maintenance and Repair 

Should you ever need to repair your MOKI engine, genuine spare parts are available through your 

MOKI dealer. Do not disassemble the engine unless you have the necessary skills, practice and tools. 

Please note that any disassembly by unauthorized persons will void the manufacturer’s warranty. 

Warranty 

MOKI engines carry a two year manufacturer’s warranty. In case your MOKI engine needs a repair in 

the warranty period, return the engine in its original packing, along with a proof of purchase, to your 

dealer or send it directly to the manufacturer. Please include a description of the problem and include 

all details about the fuel, propeller and glow plug used. 

Please note that the warranty will be void if any unauthorized disassembly has taken place. 

Furthermore the warranty explicitly excludes coverage of all damages caused by corrosion, 

overheating and crashes.