Well, 85PSI seems a little low for that engine, but you are cranking it by hand, which is tough….I would definitely rig up some jumper cables to you can crank it with the electric starter… Originally, this was a 6 volt system, but who knows what is in there now…Have a look at the starter, perhaps it will say. You can use a 12 volt battery on the 6 volt starter, provided you don’t crank it for too long a period. But, using the 12 volt battery on the choke solenoid will damage that part. Sounds like this engine is in nice original condition, all the wiring/junction box is there also? If so, you surely don’t want to damage any of those pieces…An electric start big twin from that era is quite a bit more rare than the standard recoil model. For must of us old cranks, the electric start is a much needed option….
So, recheck compression using the electric starter…
Pull the flywheel, do you have the OMC puller unit? Please don’t attempt this using some alternative puller, damage and injury can result. The ignition will surely need to be completely serviced unless someone has been in there recently…
Drain/refill the gear lube? Is the gear lube relatively clean, free of water? Older lubes were pretty dark in color so that is normal. Milky colored gear lube is an issue, raw water spells trouble. You should probably pull the gearcase and replace the water pump impeller.
The carb should be disassembled, cleaned and rebuilt as well, unless there is evidence that someone has done this work and used more up to date gaskets/etc. Finally, do you have decent pressure tank? Open the cap, have a look inside…A badly fouled/rusted tank is useless….
Feel free to post pictures with any questions you have, makes it easier to understand what you have so we can provided more useful advice/answers…

• This reply was modified 4 years, 6 months ago by fleetwin.
• This reply was modified 4 years, 6 months ago by fleetwin.

Nice Motor. It is a little nicer than mine which has faded to nearly bare aluminum on the cowl. I have about 90-95 psi compression with mine and the cylinders have seen better days. I would pull the exhaust covers and take a look inside to see how yours look.

Mine will not stay running and I’m almost 100% convinced mine is due to water intrusion through the exhaust baffle plate. I have not taken the exhaust cover off yet to see how the plate looks but I’m betting there are holes in it. Hopefully yours has not suffered a similar fate. I plan to do a complete rebuild on mine at some point unless I stumble upon a powerhead in much better condition. It is a great motor that I want to run someday.

I have two ’54 Johnson 25s. An RD-16 and an RDE-16 that are both fantastic runners and probably my favorite tiller motors to run on a boat. Well worth putting the work in to get it going. They are a blast.

-Ben

Looks like a beauty for sure…Do you have the wiring harness/junction box/switch panel? If so, you really have something special there. Don’t know if I would use the brass prop, they put more strain on the gearcase and clutch dog….