TOPIC: 1960 Merc 300 was running, but what happened?

I feel like I'm hogging the forum...sorry for all the questions. I'm trying to get at least one engine running before Thursday night so my son can take the boat out for out week off.

So, if you are connecting me to my other posts ("hot wiring Mark 55" and "Merc 300 vs Mark 55 LU") you'll see i'm working things from two sides!

The story on the Merc 300 is that, after patching it together from a spare, we tried taking it out. The first attempt we couldn't start it (battery was dead and I didn't put the upper cowl on yet). Second attempt, got it started, was peeing well, all was good, then about after about 5 minutes of idle speed and 2 - 3 minutes of medium throttle, I though to check that it was still peeing ok...it wasn't at all. Shut the engine down, (very very hot but not to the point where water would boil), paddled to shore, took it home, took apart the LU, found that it had sucked up a bunch of seaweed. Third attempt, ran ok, started to run rough but ran at full throttle reasonably well. Slowed down to switch drivers (by this time we were all smiles). When we went to speed up, there was only a slight increase in power (just above idle speed) and nothing more.

I also did a compression test.109, 108, 112, 110

Any thoughts?

Joe Poole gave me some suggestions, but it wasn't until yesterday that I notice one of the bolts attaching the exhaust cover at the top of the block had been sheered off (this was a hand-me-down block). When running it in a bucket, water was leaking from this point. I'm guessing/hoping that this is the cause of the engine not accelerating (water getting in the pistons). I've re-taped the hole but have not had a chance to test.

Ok, I know this is an old thread, but it is the continuing story.

I had some time to work on this earlier in the summer. I took apart the carb and it turns out I hadn't tightened the brass fuel assembly with the pin that controls flow of gas into the bowl (sorry, don't have my manual with me so I don't know the actual name of the part). This loosened, and of course, prevented the fuel from flowing. Turns out to be totally unrelated to the seaweed issue!

So, we got it running again (see the picture with my son and the captains hat!).....for the first week of vacation. Then one day I see my son getting a tow back to the cottage. This time it turns out that the bearing on the magneto pulley seized. Lesson learned...those grease nipples are there for a reason!!! Well, back into the garage. Won't have time until winter now!

those grease fittings don't grease the bearings. replace all 3 bearings 1 in the drive and 2 in the mag and a new belt . you will be good for another 25 years.