YAMATO ENGINES GENERAL TECHNICAL RULES
1. Engines covered by these rules shall remain in stock configuration and condition as intended by the manufacturer except where allowed by these rules. These rules are designed to give the reader the allowable modifications to these engines. The addition or removal of metal that can, in any way, be a departure of these rules is prohibited.
2. The tolerance for these engines is determined by the Technical Committee, and is shown on the specification sheets.Inspectors should refer to these specification sheets for correct inspection.
3. Any type of spray shield, spark plug boot, and throttle hook-up is permitted.
4. Any type of bracket for throttle, steering, and spark controls is permitted.
5. Any ignition advance lock down is permitted.
6. Removal of the spark advance, and gas tank handles is permitted.
7. The use of Mercury clamp brackets is permitted.
8. Adjustable kick-out brackets are permitted.
9. Cylinders may be bored or honed up to the maximum specification shown on specification sheet, and Yamato manufactured over sized pistons are permitted.
10. Water drain holes in the ignition casting are permitted. Holes may be taped and/ or plugged.
11. Spark plug thread adapters may be used on 18mm cylinder heads.
12. A replacement propeller shaft(9/1" diameter) containing only one shear pin hole is permitted on stock Yamato lower units. An adapter used on the propeller shaft to move the propeller closer to the water pick-up is permitted. Cut down Yamato propeller shafts ARE NOT PERMITTED. They will break.
13. No removal or addition of metal, nor bead or sand blasting of internal engine components is permitted. No polishing of any internal passages, cast surfaces, carburetor, or intake manifold is permitted.
YAMATO 80 Stock
1. Plugging one(1) of the two(2) water intake holes is permitted.
2. the drilling of up to a 3/16" diameter hole in the head to prevent air locks, as well as additional water outlets on the exhaust plate is permitted.
3. Reshaping the nose of the lower unit to a point vertically, and thinning of the bulb at the bottom of the skeg to match the thickness of the rest of the skeg is permitted. Other lower unit dimensions must remain in stock condition.
4. A MAXIMUM of a three(3) blade propellers is permitted.
YAMATO 102, 202, 302 Stock
1. The legal engine models are, 102C, 202D, 202E, 302F.
2. The engine cooling system must remain stock with no additional water outlets permitted. Water holes must not be plugged nor changed in size. Outlet holes may be routed at will.
3. The bulb located on the bottom of the skeg may be thinned to match the thickness of the rest of the skeg. Other lower unit dimensions must remain in stock condition.
4.Use of the 302F model ignitions used on the 202D and 202E model engines is permitted.
5. All Yamato model lower units are permitted on these engines.
6. A MAXIMUM of a three(3) blade propellers is permitted.
SUPER STOCK YAMATO ENGINES GENERAL RULES
In addition to the Yamato engine General Technical Rules, these rules will apply to the Yamato Super Stock engines. Power-head specifications to be used are corresponding stock power-head specifications.
1. Any type of down housing is permitted.
2. rotating the power-head up to 180 degrees on the down housing is permitted.
3. External water pick-ups are permitted.
4.Removal of stock fuel tank is permitted.
5.The use of an external fuel pump pressure driven off the engine is permitted. fuel filters and fuel regulators is permitted. Modifying the inlet of the carburetor to accept the furl pump arrangement is permitted.
6. Thermal barrier and anti-friction coatings are permitted.
7. Propeller with a maximum of four(4) blades are permitted.
YAMATO 80 SUPER STOCK
1. Bringing water into the block and venting water through the exhaust stack plate is permitted. However, to block any water passage in the power-head to reroute water, etc. is NOT permitted.
2. Use of the stock tuned exhaust system, which may be modified within the rules is permitted.
3. There is no measurements on the reed port size in the OEM reed block, however NO ALTERATIONS are allowed to the block, reed or shim and they must remain stock OEM parts.
4. Milling the head beyond the "H' or "I" dimension is permitted, however the head must meet CC, Squish, and Combustion Chamber specifications.
5. A float-less carburetor system is permitted. however the carburetor body CAN NOT be altered in any way. NO FILING, DRILLING, SANDING, POLISHING.
6. Notching, drilling, or slotting the top and bottom ends of the connection rod at the crank shaft end is permitted.
7. Any exhaust system, provided the block is not altered to accept the system is permitted.
8. Any type replacement parts are permitted, EXCEPT electronic ignition. Modification under the crank plate is permitted to accept the use of replacement parts.
YAMATO 102, 202, 302 SUPER STOCK, CLASS MOD 25 102 ENGINES
1. Water relief holes drilled in the block and exhaust plate are permitted.
2. Slotting of connecting rod caps to improve lubrication is permitted.
3. ONLY the model 102 factory ignition is permitted.
4. Any exhaust system, provided the block is not altered to accept the system is permitted.
5. Any lower-unit, available to the membership is permitted.
YAMATO 202, 302, class C MODIFIED ENGINES
1. Expansion chamber exhaust systems including the addition of a filler block and exhaust plate is permitted. NO OPEN EXHAUST SYSTEMS.
2. Water relief holes drilled any where in the powerhead is permitted.3. Any lower unit limited to a one(1) tooth gear reduction is permitted. ie 14:15, 15:16 etc.