1968 100 HP died after 10 mins, won't start

[NijkampTO]

We just bought a boat with a 1968 Johnson Sea Horse 100HP on it.
The owner had the engine running, although it seemed like it was misfiring or running rough.
We took it out to the lake and after about 5 mins and 5 tries we got it to start up.
It was misfiring but ran, we put it in gear and accelerated, after about 10 mins seemed to ran very nicely while almost at WOT and the boat went pretty fast.
Then all of the sudden it died..
After a couple tries it started back up but died again after a minute.
Then we couldn't get it to start anymore. We think it's a fuel problem.

Previous owner replaced PulsePack.. the boat sat around for 3 years and wasn't used.
We checked the "Hot" light by connecting the TAN wire to the engine block and it worked, and it never turned on.

Took it to a mechanic and he told us it's not worth it and couldn't get it to start..he also said the stator is melted although it looks perfectly normal(looked it up on google images).. he doesn't seem very interested. He also said that only 2 spark plugs have good sparks, one has a weak one and the last none at all.

I checked the fuel filter and it was clean along with the fuel. I think it should still fire up with 3 cylinders, but instead it just turns but doesn't fire at all anymore.

I'm thinking we should test the fuel pump and replace / test spark plugs with a cheap spark plug tester. Maybe have the carb cleaned(although its expensive and we'd like to get it running before spending much on it).. then later on change the water impeller when it runs.

I'm still confused how it can run for 10 mins then die and start up again and die and now not fire up at all.. it doesn't sound like an overheat, and we tested the overheat light..

Dirty carbs? Bad fuel pump?
What could explain the one spark plug not working? And shouldn't it fire with the 3 sparks?

Also tested compression.. seller said he tested and it was 100, mechanic said they were all around 80.. I looked it up and 80's low but it should still fire up, especially after running nicely for a while.. plus mechanic tested them when engine was cold since he couldn't get it to start.. has to be warm for it to be accurate.

Please help! We're thinking of trying other mechanics but would like to try fixing it ourselves first since the mechanic turned is down..

 

[NijkampTO]

Re: 1968 100 HP died after 10 mins, won't start

Any help would be appreciated!
Could the stator or pulse pack be bad although I'm getting 3 sparks?
With 3 out of 4 plugs sparking and decent compression.. fuel at least in the fuel line and pumping the primer.. shouldn't it be at least firing up some cylinders instead of nothing?

Thanks

 

[Willyclay]

Re: 1968 100 HP died after 10 mins, won't start

Welcome to the iboats.com forum. The experts here, which I am not, can help you with any question about your boat, motor and trailer. I also have a 1968 Johnson 100HP that will not run. Forum guru Joe Reeves told me OMC received a bad batch of wiring harnesses from its supplier in 1968 and I have verified that is my problem. You might want to check for deteriorated insulation on the engine wiring which could be causing you all sorts of problems. I hate electrical problems, especially intermittant ones! FYI, there is a wealth of DIY knowledge in the FAQ's at the top of this forum. I have provided the link below to get you started. With a little study, you should be able to check-out many things yourself. Good luck!

http://forums.iboats.com/forumdisplay.php?f=31

 

[NijkampTO]

Re: 1968 100 HP died after 10 mins, won't start

The motor ran fine, even on all 4 cylinders at one point, untill it died.
It still gets 3 sparks.. so I don't think electricity is the reason why it won't fire..
Did you ever fix your wiring harness? Which one is it that was bad? There's many..

Anybody else got any suggestions for no firing at all?

 

[F_R]

Re: 1968 100 HP died after 10 mins, won't start

Hands off that carburetor unless you know for sure it has a problem. Parts are hard to get and extremely expensive. And you need a special tool to set the float levels. Anyhoo, you obviously have a spark problem, and messing with the carburetor can't fix that.

OK, the ignition system on that motor was state of the art in 1968. But the art wasn't very good in 1968. Your problem most likely is in the distributor cap or wires. Or you could have a weak coil. The pulse pack is probably ok, since it is producing sparks.

Are you still trying to run the "right" spark plugs? The right spark plugs are wrong. The surface gap plugs require a perfect igniton system to fire them. Any yours isn't perfect. You should be running L77JC4 plugs gapped at .030"

 

[NijkampTO]

Re: 1968 100 HP died after 10 mins, won't start

I was just about to replace the spark plugs with those you mentioned, it has some cheap Autolite ones in it.
I don't think the motor has a coil if I'm not mistaking. It seems to have a stator and the power pulse pack.
I'm about to test the stator and replace the spark plugs.
How do I get to and test the distributor cap?

 

[NijkampTO]

Re: 1968 100 HP died after 10 mins, won't start

What should the stator resistance be on my motor? Manual is arriving later this week

I'm measuring 0 ohms, although the mechanic got 3 plugs to spark.. does that make any sense?

 

[cmass494]

Re: 1968 100 HP died after 10 mins, won't start

What should the stator resistance be on my motor? Manual is arriving later this week

I'm measuring 0 ohms, although the mechanic got 3 plugs to spark.. does that make any sense?

Did you ever resolve this problem? I ma having the exact issue with my 68 100hp Johnson. Runs for 15 minutes and then dies and then cannot get started. Frustrated and could use the advice!

 

[Willyclay]

Re: 1968 100 HP died after 10 mins, won't start

cmass494, this OP has not posted since August 22, 2010, when he had the gearcase off with seal problems. You can read his other posts to get further insight but he never posted about any fixes or success with this thread's problem. You should start your own thread and maybe you can get some help with yours. The members here are great but be prepared to purchase an OEM factory service manual. Good luck!