HB engines have been manufactured in West Germany since 1971 and enjoy a worldwide popularity because of their outstanding performance.

HB engines include the American Perry carburetor as standard equipment, thus, they not only achieve excellent performance in use, but are extremely reliable at all speeds, down to the lowest idling speed. The designer and manufacturer selected this combination of engine and carburetor in their endeavor to make a high performance and absolutely reliable engine. The current advanced state of modeling technology makes it essential that the engine be reliable at all speeds and that stalling is precluded even at the lowest speed.

The production machinery used in the manufacture of HB engine guarantees tolerances, which are so close that an interchangeability of parts is assured not only now, but also in the future. Because of these close tolerances, a break-in period of one to two hours is recommended.

For the many modelers who are well acquainted with the use of model engines, we are providing a summary of our instructions. However, it will be to your advantage to review the full text of our instructions carefully to assure that you will be able to fully enjoy the full potential of your HB engine as well as to understand the differences between the high performance HB and conventional model engines more.


1. Mount the engine very solidly on the motor mount.

2. The fuel tank must be located as close as possible to the engine. This is particularly important for aircraft which were originally built for rear intake engines. The centerline of the tank must be in line with the needle valve when the model is held in a horizontal position.

3. To break in the engine, any commercial glow fuel to which 20% oil have been added may be used. (Break-in time: 1 to 2 hours). After the engine is fully broken in, any commercially available glow fuel, including racing fuel, may be used.

4. The engine runs on a mixture of fuel and air. The ratio of fuel to air determines how rich or how lean the engine runs. The mixture also determines how fast or how slow the engine runs.

Full speed is adjusted only with the main needle valve. Turning the needle valve clockwise (in) leans out the mixture; turning it counterclockwise (out) enrichens the mixture.

Idle speed is set by adjusting the idle screw which limits the travel of the barrel. The idle mixture is regulated as follows:

- PERRY CARBURETOR: by turning the idle disc.

- HB CARBURETOR: by turning the idle needle valve. The idle needle valve regulates the mixture to the upper mid-range (about 75%) of the barrel travel, automatically, and perfectly.

A detailed description follows under "Carburetor Instructions".

5. For HB engines of .40 cu.in. and larger, we recommend HB glow plug no. 7004, or the K&B glow plug with the idle bar. For HB engines from .12 to .25 cu.in., we recommend the regular K&B glow plug (without idle bar).

The special glow plug No. 7018 is recommended especially for engine operation with tuned pipes, and is extremely suitable for hot running car engines. Any other commercially available glow plug manufacturer are followed.

6. To start the engine either cold or hot, the throttle must be set at idle.

7. A suitable propeller must be selected for the size of engine you are using.

8. The engine must be properly maintained and cleaned.


The engine must be mounted solidly on the motor mount. Supports made of rubber or similar material are not acceptable. Sufficient space must be provided for the exhaust or muffler. HB engines have been designed to include the muffler as an integral unit, and changes in the original assembly may cause a reduction in power.

Running the engine without the muffler will not increase its power or speed; only the noise level will increase. This is why for reasons of noise abatement, the engine should be run only with its muffler.

For all the model size .21 through .61, we offer tuned pipe mufflers to increase power, and reduce noise.

On HB engines from .12 to .25 cu.in. displacement, the muffler is fastened with single screw which is inserted through the muffler into the muffler bridge on the crankcase.

On HB engines from .40 to .61 cu.in. Displacement, the muffler is attached with two screws directly onto the crankcase.

The carburetor has the customary short needle valve which is adequate for models without an engine shroud.

Because of the very fine needle thread, no heavy mass must be attached to it. To lengthen the needle valve, as is sometimes required, insert a .040" wire into the hole which is provided on the needle valve knob, or on the brass bushing which is provided in the accessory bag. Solder the parts together after thoroughly cleaning and lightly sanding with medium fine emery paper. Bend the wire 90 degrees at the desired length, and cut the end to about 1/4". This gives you an extension which is light enough to prevent any damage to the thread.

  The fuel tank must be positioned as close as possible to the engine. This may be disregarded to a degree on car or boat models, but must be strictly complied with on airplane models. Because of the continuously changing flight altitude of the aircraft, the suction height which determines the fuel pressure changes constantly, and the fuel mixture fed into the engines may vary from lean to rich. The closer the tank is located to the engine, with the needle valve on exactly the same level of the tank centerline, the leaner you can set the fuel mixture, and the more efficiently the engine will run, because the pressure differences will be smaller. When using the Perry fuel pump; and pump carburetor, the position of the fuel tank is irrelevant.

The break-in time shall be one to two hours. To achieve the greatest power and the best running qualities of the engine, we recommend the use of a fuel filter. We also recommend the use of a large diameter/low pitch propeller. The break-in can be done on the bench.

It is recommended that this break-in be done with a very rich fuel mixture, and in short periods not exceeding five minutes in duration. If you can manually activate the throttle during break-in, the engine does not have to be stopped, but can be alternately run for 5 minutes on high throttle followed by one minute at idle.

After a total run of about 30 minutes, you can increase the speed by leaning out the mixture; you can now also use a smaller prop. CAUTION: Never run an engine in a closed space.

Experienced modelers may want to break their engine during flight. In this case, the carburetor must be adjusted to a very rich mixture, and the model must be flown with the throttle being alternated from high to low settings. This method has proven to be the best for the HB engines.

REMEMBER: The top performance of the engine may only be expected after the full break-in period is completed.


As indicated, HB engines are supplied either with HB, or with Perry carburetors.

A. PERRY CARBURETOR: Idle adjustment by means of the idle disc.

The idle disc is equipped with two O-rings which may stick in a new carburetor. Before you attempt adjusting the carburetor, let a generous amount of fuel run into the carburetor; then use a screw driver to turn the idle disc to the right and left to permit some oil to cover the O-rings. Reposition the slot of the disc on the center mark. Proceed now to adjust the carburetor for full throttle. Open the barrel completely, and adjust the mixture by turning the needle valve. Turning it clockwise leans out the mixture, turning it counterclockwise enrichens it. To insure that the engine runs properly when the model climbs vertically, you must hold it vertically with the engine running. If needed, you slightly open the needle valve until the engine runs smoothly in this position.

After this is done, you adjust the idle speed by setting the screw which is located by the air intake.

The idle mixture is adjusted by turning the idle disc with a screw driver. If you turn the disc towards (-) the mixture becomes leaner, and in the opposite direction towards (+) it becomes richer.


If the carburetor is properly adjusted, the engine runs smoothly even at the lowest idling speed. Also, it must pick up speed even after lengthy idling smoothly without bucking.

B. HB CARBURETOR: Idle adjustment by means of an idle needle valve.

Open the main needle valve two full turns and start the engine. Open the throttle completely and close the needle valve until you reach maximum speed. You have now adjusted the carburetor for best performance at full throttle.

Close the throttle now to half position, and turn the idle needle valve clockwise. If the engine misses and four-cycles, the mixture is too rich, and must be leaned out by further tightening the idle needle valve until the engine runs smoothly.

If the engine stops at half throttle, the mixture is too lean, and must be enrichened by untightening the idle needle valve until the engine runs smoothly. Move the throttle now to "idle" (almost closed), and repeat the fuel mixture adjustment. Fix the idle position by means of the idle set screw. This completes the carburetor adjustment.


In the summary, we have recommended the HB glow plug No. 7004, as well as K&B glow plugs, with or without the idle bar. The selection of the glow plug depends to a great degree on the type of fuel used, and on the weather conditions. Different types of glow plugs will provide different performance under different conditions; this means simply that a glow plug regardless of make cannot be judged after a single flight due to these variables.

The HB glow plug No. 7004, and the K&B glow plug with idle bar are relatively "cool" plugs. They are recommended for use with regular or racing fuels in warm weather. In cold weather, their use is recommended with "hot" fuels. It is suggested that, in the winter, a small quantity of racing fuel be added to regular fuels, to increase nitro contents somewhat.

To meet the increased demands of engines with tuned pipes, our glow plug No. 7018 was developed, which is also very suitable for car engines. The K&B glow plug, without idle bar, is relatively hot plug. It is recommended for use in cold weather with regular fuels. They are also recommended for marine applications in which the engine is well cooled. These four glow plug types are designed for 1.5 volt operation. If you use a 2 volt starting battery, it is recommended that a connecting cable 20 gauge stranded wire of 4.5 to 6 ft. in length be used between the starting battery, and the glow plug terminal. When properly used, glow plugs have a long and useful life. However, it is recommended that glow plugs be examined and replaced after a reasonable period of time, because of deposits which form on the coil and which are detrimental to proper ignition action, and affect the power and starting qualities of the engine.


The engine must be started at idle when hot as well as cold. If your engine was stopped only for a short while, it is usually sufficient to just flip the propeller. However, if the engine has cooled off, the engine must be primed at the carburetor, and turned over several times by hand. If the idle speed is correctly set, the engine will start at once when the glow plug is connected. The HB .12 and HB .15 are primed through the extra hole in the muffler.

To start the engine, fill the fuel tank, prime the engine by squirting a small quantity of fuel into the carburetor, or (on the HB .12 and HB .15) into the muffler, Turn the propeller over a few times counterclockwise to expel any excessive amount of fuel through the exhaust slots. This leaves a mixture in the cylinder which is suitable for a fast start. Turn the needle valve counterclockwise two to four turns, and connect the glow pug to your starting battery. The engine will start after flipping the propeller. Disconnect the glow plug cable after about 5 seconds. Before the model is launched, check the throttle through its entire range. To do this, hold the model vertically with the engine pointing straight up. The engine must not stop. If it stops after briefly accelerating, unscrew the needle valve slightly, and repeat this procedure until the engine runs properly in the vertical position.

Be careful not to flood the engine -- this is particularly important with the HB .12 through HB .25 due to their small displacement. The combustion chamber is easily flooded, and the fuel remains liquid with no possibility to gasify. This causes "HYDRAULIC LOCK". In such case, it is recommended to remove the glow plug, and turn the propeller a few times. Replace the glow plug, and repeat the starting procedure. By forcing the propeller to turn over, you may break the crankshaft and/or connecting rod.

  To select the correct propeller, the aerodynamic qualities and the weight of the model must be considered in addition to the engine size. Which propeller will give you the best efficiency must be determined by tests with your own model. If you lack experience, your engine dealer will gladly assist you to specify a number of prop sizes from the performance curve of the engine. In all cases, balanced propellers assure a vibration-free operation, and thus better overall results. This becomes even more important with larger size propellers. For this purpose, we include with all HB engines from .40 cu.in. and up, a balancing bushing. This aluminum bushing a .040" wire is inserted into the propeller bore. Resting the wire ends on two supports of equal height will permit you to determine the imbalance of the propeller, if any. The condition may be corrected by lightly scraping the heavier blade with a knife, or lightly sanding the back of the heavier blade with fine sandpiper.

If you have used racing fuel, run the engine after completion of your flights briefly with regular (FAI or 5%) fuel. This is recommended because the additives in racing fuel often corrode some of the engine parts, especially the aluminum parts. Note also that racing fuels shorten the life of the glow plug.

When the engine is not in use, it should be wrapped in a clean linen cloth, for protection from dust and other dirt. If the engine needs cleaning, spray engine cleaner or filtered kerosene through the intake and outlet openings of the cylinder and crank the engine over several times by hand. After cleaning, insert a few drops of lightweight engine oil into the same openings, and crank the engine again by hand. If the engine resists cranking, do not force it, but turn in the opposite direction. (Hydraulic Lock Disk)

  From time to time, it may become necessary to clean the carburetor. Fuel residue and other dirt may clog the carburetor nozzles, as well as the adjusting screws and needles. Remove the carburetor from the engine, remove the needle valve, and the retainer clip. Mark a line in the idle mixture disc reference slot with a sharp instrument, then grasp the idle mixture disc and rotate back and forth as you pull it from the carburetor body. After untightening the idle set screw, you can remove the barrel pulling at the lever. If you find oil or grease residues in the slot of the idle mixture disc, remove them with a sharpened piece of wood (toothpick is OK). Never use metal, such as pins, needles, or a knife. Never remove the O-rings, because they may be damaged. If they are properly handled, they last as long as the carburetor lasts. After cleaning, reassemble the carburetor in reverse order.

After untightening the carb set screw, you can remove the idle set screw. The barrel can then be removed from the carburetor body. Then remove the spring from the body. After marking its position, you may now remove the main needle valve. Clean the fuel port in the body, and the jet in the barrel with fuel (or simple methanol), reassemble, and if necessary, readjust the needle valve positions.

CAUTION: Use only mild solvents, such as gasoline, kerosene, or alcohol. Immerse it briefly in the recommended solvents, and immediately dry it thoroughly. Do not soak in any solvent, such as acetone, lacquer, thinner, carburetor cleaner, etc.


The HB .21 Grand Prix is an ABC (aluminum piston/brass, chrome plated sleeve), Schnuerle porter engine whose exhaust can be rotated to the right, left, or rear of the engine. This allows the modeler to select the most suitable position of the exhaust for his model.

The position of the exhaust must be selected before the engine is broken-in for best break-in results.

To position the exhaust, proceed as follows:

1. Unscrew the four cylinder head bolts.
2. Remove the cylinder head.
3. Remove the cylinder head insert, but save the head shims.
4. Remove the ribbed upper crankcase portion by unscrewing the four bolts which hold it to the lower crankcase. (NOTE: The sleeve remains in place, held by a pin which is provided for this purpose).
5. Rotate the upper case portion to the desired exhaust position (90 degrees to either side).
6. Reassemble in the exact reverse sequence.

CAUTION: Be very careful when tightening the case and head bolts. Tighten slightly until the bolts set; then tighten fully in a crosswise fashion.


Our name is your assurance that the HB engine you have purchased is a carefully developed product, manufactured to the highest quality standards under continuous and meticulous quality control. We consider it our obligation to provide you with an engine which will always give you maximum performance, reliability, and pleasure.

Technical modifications aimed at the improvement of the HB engines are under continuous consideration, and may be introduced at any time without prior notice.



©2005-1998 Model Engine Corporation of America, All rights reserved.
HB is a Trademark of Model Engine Corp. of America

No part may be reproduced without written permission from
MECOA -- P.O. Box 98 -- Sierra Madre, CA 91025 U.S.A.