rspencer129
New member
I am at wits end with my motor. It is a 1990 Mercury XR4 150 6 cyl. 0C249018. The boat will not plane. It will not get above 12 mph. It will idle great and take me out of the wake zone but, when I apply throttle it just won’t get full throttle and go. It sputters and just wont go. I’ve had it for 3 years and it has worked great in the past. The onset of the issue was sudden and has not ran up to max power since.
What I’ve done so far:
Carbs. Link and sync. Checked float levels. Fuel does spray into the carbs as throttle is applied. Butterflies open all the way when full throttle is applied. Fuel mist comes out of each cylinder when plugs are removed and it is cranked over.
Fuel. Drained tank and replaced with fresh fuel mixed 50:1 (oiler deleted). Added seafoam. Replaced fuel line on boat and motor. Replaced fuel filter with inline 60 gph filter.
Electrical. Motor was only firing on 2 cylinders. Replaced switch boxes and now have spark to the plugs on each cylinder. Replaced spark plugs (NGK BU8H). Disconnected temp sensors and warning box. Stayed the same so I reconnected.
Lower unit. Replaced impeller. Replaced prop with new same type prop as previously on it. Exhaust comes out quite a ways past the prop on muffs when throttle snapped.
Ignition. Set timing to 19 deg with idle stabilizer disconnected. Idle at 11degrees. Also ran on water at 23 degrees with stabilizer disconnected, no change. Linkage has full range of motion.
Compression is 135 on all cylinders except #2 which is 120.
I don’t know where to go next. Any and all help is greatly appreciated.
What I’ve done so far:
Carbs. Link and sync. Checked float levels. Fuel does spray into the carbs as throttle is applied. Butterflies open all the way when full throttle is applied. Fuel mist comes out of each cylinder when plugs are removed and it is cranked over.
Fuel. Drained tank and replaced with fresh fuel mixed 50:1 (oiler deleted). Added seafoam. Replaced fuel line on boat and motor. Replaced fuel filter with inline 60 gph filter.
Electrical. Motor was only firing on 2 cylinders. Replaced switch boxes and now have spark to the plugs on each cylinder. Replaced spark plugs (NGK BU8H). Disconnected temp sensors and warning box. Stayed the same so I reconnected.
Lower unit. Replaced impeller. Replaced prop with new same type prop as previously on it. Exhaust comes out quite a ways past the prop on muffs when throttle snapped.
Ignition. Set timing to 19 deg with idle stabilizer disconnected. Idle at 11degrees. Also ran on water at 23 degrees with stabilizer disconnected, no change. Linkage has full range of motion.
Compression is 135 on all cylinders except #2 which is 120.
I don’t know where to go next. Any and all help is greatly appreciated.
