SHORTHAIR DUDE
New member
Hi all, brand new to the forum here. Having a issue with a Mariner 40hp magnum Ser# 0D036677, I think its about a 1990. A little backstory on it, I got the boat this summer hadn't ran since last year, got it running and took it out ran okay, would get up on plain slowly but was no power house (on a 16' smokercraft). Second trip out made it about a mile up the river and lost power, was like only having half throttle. Got back in and checked it out, and had no spark on the lower 2 cylinders. Upon inspection the wires from the trigger coil were rubbing against the flywheel, fixed that problem and had to replace the CDI box as well to get spark back on the lower cylinders, had to replace the rectifier as well. So now have great spark on all the cylinders, the stator is charging after replacing the rectifier, the trigger coil and stator both ohm out in speck. But the lower cylinders #3 & 4 are still not firing, compression checked all the cylinders three times now, and they are all at 140 psi. Removed the lower carb and went through it completely , inspected the Reed valves while the carb was off, visually they looked fine, stuck my pinky finger in and felt them up couldn't feel anything wrong with them. After getting the carb back on the lower cylinders still won't pull themselves. Doing the drop test removing the spark plug wires while its running the lower two cylinders will seem to fire a little but if you remove the plug wires on the upper two cylinders the engine dies immediately . Now when its running we've tried spraying the lower carb with carb spray and the lower cylinders still don't pickup. We put spark checkers on all four cylinders while its running and it has great spark on four cylinders. We even removed the fuel pump and blocked off the port and ran it to eliminate a vacuum leak there and no change. Removed the side plate for the exhaust chamber to inspect the pistons and cylinders to see if the lower half of the cylinders were scored to where it couldn't build pressure in the crankcase, but the cylinders and pistons look fine, just like the upper two. Now when running when you put your hand in front of the top carburetor and it wants to suck your hand in, definite vacuum, the lower carb doesn't feel like it has hardly any vacuum. Did the paper test with putting a piece of paper in front of the carb while running to see if its spitting fuel back out like a bad reed valve, but that didn't yield a definite answer, didn't seem to have any fuel pushing back out of the carb. So what I'm too is possibly the lower crank seal could be blowed out and not letting it build crankcase pressure for the fuel to suck into the cylinders, would that affect both the lower cylinders?? Cracked block possibly, but I don't know how that would happen, and the motor is in great shape, all the paint on the engine is the same color doesn't appear to ever have gotten to hot. Now its basically the Classic 50 which doesn't have a head gasket at all. Or the reed valves could be bad but didn't visually appear to be, but what I've read this style of engine didn't have much reed valve trouble. So just looking for any suggestions before I pull the powerhead out and dig in deeper. Sorry for writing a darn novel, just want to be thorough, been pulling my hair out with this darn thing. I will add that I haven't done a leak down test yet on the lower cylinders just compression tests. Any help is greatly appreciated, Thanks!