yamaha, f115 4stroke 2001

by jeff k
(ne iowa)

motor starts good and seems smooth up to 1800-2000 rpm then starts to drop cylinders 3 and 4? water pump and thermostat good. new 91 octane gas non ethanol sea foam 1oz per gallon. spark plugs 1 and 2 read light white/sand plugs 3 and 4 read brand new as if they havent run at all. dual sided coils 1 and 4 share and 2 and 3 share. ran for 15-20 minutes on garden hose and engine oil dip stick says it made oil. crank case is full. do i have a coil problem or an injector problem? put in 4 new spark plugs everything exactly the same. 1 and 2 good 3 and 4 look silver and new. checked compression cold 1 is 162 2 is 160 3 is 160 4 is 160. balanced across all four. new to fourstrokes can any one help me diagnose why 3 and 4 arnt working over 2000rpm and why motor added gas to crankcase made oil?

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