99 Saltwater 115 won't rev over 2000

[awaschka]

Hi everyone. I have a 1999 S115 that has had a problem almost since new. At least three mechanics have worked on it including one dealer, but no luck. Usually it will be OK for a while after coming back from the shop but always gets the problem back. Various things have been diagnosed, mostly related to overheating, but there has never been a permanent fix.

Most of the time the motor starts hard when cold. Idle is rough, and it sounds like a miss below 2000 rpm. It will rev high in neutral but runs rough with a lot of noise which seems to be caused by missing. Under load, most of the time it will not take throttle above 2000 rpm, it bogs down and dies. Occasionally if I sneak up on it by running the throttle just before the speed where it dies for a few minutes it will smooth out and then I can give it throttle. Once throttled up it runs fine until I throttle back. I have a built-in gas tank with new fuel, a new water separator in line, and I have tried switching to an external tank with no change. Any ideas?

Thanks,
Al

[awaschka]

Update

I have tested by removing spark plug wires and moving plugs from side to side. I was pretty sure the plugs were bad; cylinder 2 appeared dead, plugging and unplugging the spark plug wire made no difference in the way the engine ran, but it had good spark because I could hear it jumping to the plug. I checked timing by the specs in the shop manual. It was off a little, but not enough to make the engine as bad as it was. I checked the compression and it looks good. The "dead" cylinder is the best of the lot. Then I settled in on fuel. If I get the engine just running rough under load and press the key to enrich the mixture, it speeds up momentarily before dieing. So I think it is fuel starved. The fuel filter had a pretty good amount of crud in it so I cleaned it all out. I pulled the 1-2 carburetor and tore it down. There was some very fine dirt in the bowl and evidence of varnish. I soaked it in cleaner and reassembled it. I ran out of time before I got the 3-4 carb off, but maybe I can get that done tomorrow night. I'll post the results.

[awaschka]

Finally! It's Working!

I have tested by removing spark plug wires and moving plugs from side to side. I was pretty sure the plugs were bad; cylinder 2 appeared dead, plugging and unplugging the spark plug wire made no difference in the way the engine ran, but it had good spark because I could hear it jumping to the plug. I checked timing by the specs in the shop manual. It was off a little, but not enough to make the engine as bad as it was. I checked the compression and it looks good. The "dead" cylinder is the best of the lot. Then I settled in on fuel. If I get the engine just running rough under load and press the key to enrich the mixture, it speeds up momentarily before dieing. So I think it is fuel starved. The fuel filter had a pretty good amount of crud in it so I cleaned it all out. I pulled the 1-2 carburetor and tore it down. There was some very fine dirt in the bowl and evidence of varnish. I soaked it in cleaner and reassembled it. I ran out of time before I got the 3-4 carb off, but maybe I can get that done tomorrow night. I'll post the results.

Well it took a lot longer, because there were more problems, but everything seems to be fine now. I cleaned the carbs but still had the problem when I put them back in. After trying a bunch of things, including new plugs and a new fuel filter, I pulled both carbs to make sure that the idle passages were clear. One of the nuts holding the carb to the manifold was loose (Duh!). The floats were out of adjustment, maybe because I didn't pay attention to which side they were on when I initially disassembled the carbs. So I got new bowl gaskets (ouch - $50 list $30 discount, but the new ones are neoprene instead of cardboard), cleaned and blew out the carbs, and reassembled the carbs checking everything to spec like I should have done the first time. I also found the source of the hard starting - the o-ring that holds the electric solenoid linkage on the choke cam was missing and the linkage wouldn't stay on. Today I started it after running it dry last week. Pumped up the bulb, hit the electric choke, and it started after about 4-5 turns. Never done that before. Idle speed is stable, transitions to full power smooth as can be, stays smooth after it warms up, in all, working like it did when new and hasn't since the first time it went into the shop when my brother-in-law owned it.

Now I'm ready to sell it and get my Merc 115 back on the boat - this thing is too heavy!