Yamaha - after 27 year nap...with VIDEOS

[DonV]

OK...I'll give you some credit, it hurts to do that!! But I just thought "maintenance" in your book was putting gas in the tank and two stroke oil in the gas

[Bushwacker]

Jim,

Sounds like that was money well spent! I guess a motor as new as an '88 (my old carb'd motor was a '75 vintage) probably has an oil injection system. However if it just mixes oil with the gas upstream of the carbs instead of injecting oil directly into the bearings and cylinders, it's still basically the same as running premix. If that's the case, running the motor with a plugged carb jet starves that cylinder for OIL as well as fuel, and that can quickly kill a motor!

I had a plugged jet on my old motor one time, but since I was definitely NOT overpowered (~100-105 prop hp on a 20), it was pretty obvious I had a problem, so I discovered it right away. However, one potential issue with a bigger motor that will push a boat over 40 mph is you can have a potentially fatal problem like fuel starvation, but with lots of power available, it's easy to just bump the throttle up a bit and never notice it until it's too late!

If you consider that modern motors are calibrated to run leaner mixtures for better fuel economy, and add e-10 (10% ethanol) gas that contains extra oxygen and burns even hotter if the mixture gets lean, there is not a lot of margin between normal operation and a slight amount of fuel starvation that can lean out a cylinder enough to overheat a piston/score a cylinder, etc.! The older carb'd motors like yours were jetted on the rich side of optimum for maximum power, so it was hard to plug 'em up enough to hurt 'em, but that's no longer true for the modern "clean technology" motors, either 2 or 4 stroke! I'd advise anyone running a modern engine to be very cautious about just bumping the throttle up a little more if it doesn't seem to be running right! While some of the bigger motors have knock sensors or O2 sensors that may detect lean operation, I believe a little extra caution is warranted if a modern motor seems to be down on power! Although I've never had that sort of problem on my E-TEC, my dealer has measured the restriction in the boat's fuel system, I run a vacuum gauge downstream of the fuel filter to check for plugging, and I watch the Throttle Position Sensor reading vs. rpm relationship for anything unusual. One time that alerted me that I had forgotten to pull up the swim ladder, so it seems pretty sensitive! If I was running a 4-stroke and didn't have a TPS readout, I think I'd monitor intake manifold vacuum, as it's also a very good indicator of engine load.

[captbone]

Nice. Congrats. I would bet a new modern SS prop would give you 2-3mph and better fuel economy as well.

[Capt Terry]

I replaced the original '76 Merc 150 straight six on my '76 Seafari in 1985 with a Merc 150 V6. This second engine ran for 28 years until the summer of 2013 with the first 15 years in salt water in south Florida. The remaining usage was on SC fresh water lakes for watersports. It received relatively routine maintenance, but the carbs were never rebuilt (thanks to annual replacement of the water separating fuel filter) until 3 years before she died. The mechanic who gave me the low-compression death warrant told me I got twice as much out of it as I should have considering salt water usage!