Like stated above, they let the water flow out when the T-stats open up. And are also your primary exhaust outlet when the engine is idling in the water. This is the reason why MOST 2 stroke outboards idle real fast on muffs, and then come back down to normal in the water. 2 strokers are EXTREMELY sensitive to exhaust back pressure, espescially at idle. Just ask some hot rodders what happens when you open the exhaust on a 2 trsoke without adding fuel
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2011 SUNDANCE B20CCR SKIFF, 2011 YAMAHA 90HP 4 STROKE, 2011 KARAVAN SINGLE AXLE ALUMINUM TRAILER, LOWRANCE ELITE-7 HDI, MINN KOTA RIPTIDE TROLLING MOTOR
2000CC HYDRA-SPORT 225+HP EVINRUDE SOLD
AND THE PINK JEEP!!!! R.I.P.
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