74 15hp sea horse are they junk?

[45ACP]

Hi folks,

I recently got a hold of a 74 Johnson 15hp model #15R74S. I bought it knowing it didn't run very well but figured I could fix it and have a good motor for cheap. Now I'm wondering if I made a big mistake.

Here is what it's doing, it's hard to start and when it finally does it will idle OK but not real good. At full throttle in forward gear it won't even blow water out of a 55 gal. barrel. When I come out of full throttle it will usually die and is hard to restart.

I went to a marine repair shop who has a pretty good reputation and he told me that my particular year model is basically junk. He suggested I get it running as best I could and get rid of it. He claims 74 thru 76 9.9s and 15s were S--t! "they took three years to get it right" is what he said. Anyone ever heard this? Agree or disagree? Anyway I would like to get it running. Here is what I know.......

1-New plugs
2-All new fuel lines
3-rebuilt fuel pump
4-carb removed disassembled and cleaned
5-by-passed fuel connectors
6-Ran from gas can eliminating tank problem
7-points cleaned and gapped (recently replaced)
8-coils were replaced before I got it
9-compression 118 and 120
10-timing ring moves freely
11-both plugs have spark
12-pumping fuel bulb doesn't help
13-rich/lean adjustment on carb only changes the way it idles

all this and no significant change, there was some change after rebuilding the fuel pump. One time during all this it woke up and blew water everywhere and then promptly died and when restarted it continued it's sluggish behavior.

Can anyone help me out? Or should I just take the shops advice and cut my losses? He also said he has never seen one in those years that ran real good.
Any input is welcome and appreciated. I usually get good help on these kind of forums and I suppose this will be no exception.

Thanks.

 

[Okee Jimmy]

Re: 74 15hp sea horse are they junk?

What you describe sounds like it is dropping a cylinder. An inductive timing light on either of the plug wires will tell you if a cylinder is losing spark while running.

The only significant difference between the early 9.9's, and 15's was the ignition system. The 74-76 motors used what OMC called low tension ignition. It used a driver coil located under the flywheel, and two ignition coils located on the powerhead. This ignition system didn't produce spark as hot as the later models 77 and up. I have retrofitted the later model ignition to the older model motors, but you will need flywheel, timer base, coils, and power pack, and will have to fabricate a mount for the power pack. I picked up the whole ignition system on Ebay for under $100. and it was worth the investment.

The early ignition wasn't horrible, but it had its quirks. The ignition system on this motor should be able to jump a 3/8" gap at cranking speed. If you find that your motor is losing spark on a cylinder, it may have a weak driver coil. Also I always use a little contact cleaner on the points before installing them, as sometimes extended shelf life may form a film on them, preventing them from making good contact.

And for 13, this is correct. The high speed circuit of this carb is metered by a jet in the carburetor body inside the float bowl, the mixture screw on the carburetor controls the low speed mixture only.

 

[45ACP]

Re: 74 15hp sea horse are they junk?

That's a good idea with the timing light. Thanks for the feedback. I'll try that tomorrow.

 

[JB]

Re: 74 15hp sea horse are they junk?

I am amazed that an engine 34 years old and presumably in successful service for most of that time suddenly becomes "junk" when a tech fails to correctly diagnose and repair a problem.

I had a '74 15 that ran flawlessly until it was stolen. I bought it new from the OMC training center where it had been a training fixture for a year.

 

[CATransplant]

Re: 74 15hp sea horse are they junk?

When you say you disassembled the carburetor and cleaned it, did you remove and clean the main orifice? How did you clean the carb? Did you install a carb kit? Did you remove any round plugs and blow out the passages under them?

 

[F_R]

Re: 74 15hp sea horse are they junk?

Well, folks, let me tell you something: I was a dealer mechanic in 1974 and we had a LOT of trouble making those things run. They seemed to be OK on some boats, but on others were impossible. People bought them for use as sailboat auxillaries because of the available reverse thrust kit, extra long shaft, electric starter, etc. We couldn't keep them running for one weekend on a sailboat!! OMC came out with at least 6 or 7 "fixes" guaranteed to work and none did. They replaced cylinder heads, carburetors, ignition, and a bunch of other things. I would call the motor in and install the kits, send it out running fine on Friday and it would be back on Monday morning. After awhile you couldn't sell one of those motors to a sailboater on a bet. I changed careers in 1978 and those 9.9 and 15hp motors still didn't run. I reckon they did get better after they went to CD ignition though.

So don't be badmouthing the shop. He knows whereof he speaks. If it were not so, then OMC wouldn't have come out with all those fixes.