newbie questions Johnson 10 hp 1960

I have been lurking here for a while and I have gotten a lot of good info from doing searches. This is a great site!

My stepfather gave me an old 12' starcraft boat and trailer a few years ago and I am now getting around to fixing things up a bit. The motor has always "ran good" but I know that it has had NO maintenance (except for a new set of plugs) in at least 10 years. Before that I can't be sure.

So I decided to work it over. I got a Seloc manual and I cleaned the carb and replaced the float, replaced all the fuel lines and a put in a new impeller. I have new points and condensers that have yet to be installed.

Now, I have several questions:

#1 - I checked the compression as is and I got 77 and 80 or so psi. Apparently I should have run it and decarbed before I can get a reliable reading? Is that right? Plus, I have read here that it should be 90+ but the difference between cylinders is more important, which begs the question: how low can the compression get before I consider ripping into the powerhead?

#2 - I took the flywheel off to install the points and condensers and I see that the coils are cracked. (new ones are on the way) So when I go to install them and push the wire into the coil, should I clean or trim the end of the wire first for better contact? Or should I just replace the plug wires?

#3 - I don't know how old the prop is, (it's the same color as the motor, could it be OEM?) but overall it looks pretty decent but it fits a "little" loose on the shaft. I measured the prop and shaft and there is only about .010" difference. How loose is too loose? I can definitely get wiggle out of it. I asked FOUR different buddies of mine and I got FOUR DIFFERENT answers. I don't really want to spend $70 on a new prop just to find out that the old was was really OK.

#4 - When my stepfather bought the boat he was told that the motor runs good, never had any trouble but it would never plane out that boat. So he put a stingray on it which did cure the problem, but that seems like a band-aid to me. Should this motor (if it is running correctly) be able to plane out a 12' aluminum semi-vee rowboat?

Thanks in advance.

Re: newbie questions Johnson 10 hp 1960

replace the plug wires also. tilt the motor up, adjust the piston so the are about 1/2 way, and soalk over night with marvel mystery oil. then tilt it back up an clean up the oil. and gently rotate the flywheel to get the rest of the oil out. the prop should be ok. yes it should plane a 12 ' tinny. but you must have weight in the bow. i had a 14' tinny 55 15 hp , i put remote control and stick steering at the middle seat so i could fishing alone.

Re: newbie questions Johnson 10 hp 1960

Your compression readings sound low, but that could just be the tester itself. If it seems to run fine except that you don't have enough power then its likely just those bad coils. A 10 hp should plane a 12' row boat easily. My 10 hp motors (I have 4 of them from the 50's) all push my 12' boat at 20-21mph (GPS) and the boat is rated for a 12.5hp.

Since you are replacing the entire ignition you might as well get new plug wires. 47 years is long enough.

Your prop can have a little play in it. Also, that play is a result of the prop nut not the prop.

Report back once you've replaced the ignition and gave it a test run.

Re: newbie questions Johnson 10 hp 1960

Oh I definitely will. I'm sure I'll have more questions anyway!

Thanks for the help.

Re: newbie questions Johnson 10 hp 1960

Ok so I finished replacing the ignition and put it all back together except for one screw and a fuel line that I still need to replace.

Unfortunately I have to work all weekend but I should be able to fire it up on Monday or Tuesday!

Re: newbie questions Johnson 10 hp 1960

Ok, It started up fairly easily and I ran it for about 10 minutes. I would have let it run longer but I killed it playing with the throttle and I had broken the pull cord! (I KNEW there would be something I forgot!)

I do have a question: It ran kinda rough and shaky. I expected it to run rough for a while until I get the carbon out of it and get the carb set right, but how smooth SHOULD it be? Or did I do something wrong?

Re: newbie questions Johnson 10 hp 1960

It is supposed to float in the rubber mounts. Is that what you are referring to? Carb adjustment can make a big difference too if it is running too rich. Makes 'em four cycle (fire every other stroke).

Re: newbie questions Johnson 10 hp 1960

I expect once you take the boat out and set the carb it will run much better. Make sure you have all those rubber mounts FR mentioned. Without them the rattling will drive you crazy.

Re: newbie questions Johnson 10 hp 1960

Yeah that's kinda what I was thinking, I need to get it out on the water and set it.

I think after all the work I put into it I was hoping it would be a little smoother.

I still have to replace the rotted seats in the boat and maybe the transom, wire the trailer and get a hitch put on my car so it may be few weeks until I get to actually USE the boat. For now I'm just happy that I got the motor running again.

Thanks again for the replies.

Re: newbie questions Johnson 10 hp 1960

Without being there it's hard for anyone to judge the term "smooth". The alternate firing twin was a big deal because it helped to balance the explosions resulting in smoother operation. Also the rubber mounts were very soft so that the vibrating (shaking) motor's motion wouldn't be transmitted to the boat. But you are only firing 2 cylinders. At idle, expect some shaking. Course if it "sneezes" in N that is a big shake but happens often with those engines.....for me anyway. Once you put it in gear, it quit......sneezing and smoothed out.

One nice thing about Merc higher power engines in those days was their 4 cylinders which overcame the shakes. I bought one for that specific reason.

But I felt the OMC could outpush the Merc on a 1:1 horsepower basis.

My 2c

Mark

Re: newbie questions Johnson 10 hp 1960

once you have it running, set high speed first, then low speed without the sneezing or hicups. try to set both mid way to provide adjustments as weather and tempature change. this point in the year, you dont have long. it is important-high speed first, then low, too lean to long can burn rings, then it will never run right. this is with boat under power on water. have someone else drive if your on a busy lake. you can go about 1/8 turn rich if you like on high speed without loading up(misfiring or sneezing). you will be looking for your highest rpm on either setting, then back it down about 100 rpm as your listening. more will load it up and cause misfireing. i have a qd-20 10 hp pushing a 16'3" fiberglass tri hull and it almost makes plane with just me and no gear for fishing.

Re: another newbie here with a qd 19- 10 hp

Re: another newbie here with a qd 19- 10 hp

And looking for a lil direction for fuel oil ratio, would I be correct at 24-1, i think thats what ive been finding on here. Got this a couple weeks ago, and have been following forum, have done seals and bearings in lower unit, and new impellor, have updated with new fuel pump, instead of ole pressure system, just have to finish mounting that, and fire her up, just looking to be sure about fuel mixture, any suggestions would be helpful, thank, Steve

Re: newbie questions Johnson 10 hp 1960

You need to start a new thread about your outboard. This thread is very old. Put your model number in the title, with a couple of words about what you want to know. Someone will answer it right away. People tend to ignore new questions on old threads.

Yes, the correct fuelil ratio for your outboard is 24:1.