1963 40hp Johnson electramatic not reaching full power

Decided best i start a new thread with appropriate title...this is continuation of other thread just posted by Vandenburgh, hopefully the right call.

Update: I finally got the boat on the water today at the lake cottage so I could move beyond test barrel. Happy that engine started and idled fine, but downhill from there. Engine wouldn't hit full rpms. Didn't get too far trouble shooting as starter failed (hopefully just dead battery, but not too confident, but battery is on charger overnight). That said, before starter issue I checked and adjusted link and synch and believe that part is ok..this is how synch is working...butterfly just begins to open as marks on cam passes pointer on intake manifold as throttle is applied and continues to open as follower tracks cam as throttle is increased. when near end of cam, and throttle is pushed to WOT, butterfly fully opens....hopefully that part is right. After adjustment, tried engine again, and same issue.


So starts fine and starts out fine as throttle applied, but never reaches full power...it never fully planes boat off and it did so when last running season before last (wasn't in water last season), like it isn't getting full throttle. As a lark, I disconnected bottom cylinder to see if boat operated same way as when both were connected, and it showed same behavior whether bottom spark plug wire attached or not, so I am thinking bottom cylinder not firing at all but not sure and maybe it is something else, but thought I would mention. That is as far as I got, before my starter began acting up and not engaging (solenoid clicks, starter groans and spins a bit, but does not fully spin up)


Assuming I can get starter working (battery now on charger), what is recommended steps to trouble shoot engine not reaching full power? For now, I would like to assume compression ok as I don't have my tester with me and here through the coming weekend...and boat ran ok at WOT, maybe 20mph or so, last time on water couple seasons back at end of season).


I assume i should check status of spark on bottom cylinder as my next step. Any suggestions for next steps would be welcome as I contemplate situation while battery charging overnight (keeping fingers crossed starter hasn't gone bad!)

Running on one cylinder so the ignition system likely needs attention.

Starter worked today and I could trouble shoot power issue. Did the drop test as suggested, issue was bad plug connection, so that was an easy fix. Got it out on the water, ran it around the bay for a few minutes and all,was fine, ran really good. My son jumped on board and we ran it up the shoreline for a bit and turned it around as we didn't want to get too far away given operating history...all was good, we were happy! Good thing we turned around as we were running at about 3/4 throttle, cruising nicely when all of the sudden we came to an idle...I thought my son had throttled fully back, but throttle was still in the 3/4 open position.

we managed to coax it back home at near idle speed and just got back in as thunderstorm rolled in. I am writing this post as it is still storming, so hadn't had chance to investigate. Here is what I noticed/did and how motor reacted...

when it came to idle while throttle was still open, we pulled throttle back. Removed cowling. Reapplied throttle, same problem..pumped bulb, it was still firm...gas was in bowl. Engine block wasn't particularly hot, but generator was quite hot to the touch (ammeter on dash was showing 10amps while we were under way, so it seemed generator was working). Disconnected belt to generator for safety, as it seemed too warm vs what I had expected and figured I would just play it safe on that front. Restarted engine, applied throttle, same issue, no response, just fast idle. By the way, applying choke would cause engine to begin to stall. Anyway we fast idled back with throttle controls about 1/2 open. Also, I found that as I pushed open butterfly with my finger (son at the helm), we could pick up some speed and this is how we got back. Didn't stop and ponder while on the water given sky was changing quickly, just focused on making forward progress home.

So a moment of triumph followed by defeat...

So what might be the causes of a 1963 40hp going from running 3/4 throttle for 5 min to unexpectedly slowing to idle without anyone touching throttle? Where would the experts recommend begin the trouble shooting?