Loss of Power After Engine Warms

Hey guys,
Ok I just bought this boat a couple of weeks ago and have noticed a few issues. It has a '73 65HP in it. I knew there was an issue with the gear case before I bought. The old gearcase froze and blew the sides out. The dealer had a gear case for a '75 70HP that they swapped out now it seems forward and backward are reversed. I can live with that till I rebuild the lower end unless it revolves around the issue I am having.

Which is here: After a couple hours of tooling up and down the river (appr. 3800-4000RPM), I'll park the boat shut the motor off and do a bit of fishing (appr. hour or two) when I am done I can never seem to get the motor to do over 2300 RPM. It runs starts shuts off restarts all fine. I just have no power and can't get any RPM at max throttle.

Any ideas or suggestions?

Thanks in advance!
Rick

Re: Loss of Power After Engine Warms

Get a spark gap tester and check the spark, set gap per the service manual, mine is 7/16th inch.
Check it when its balky obviously.
Coils could be going south when heated up.

Re: Loss of Power After Engine Warms

Jones,
Hey Bud thanks I was thinking of replacing the spark plugs. I don't know when they were replaced last and is a really cheap fix. I was just looking at the price of the coils thats $150 drop right off the top if I get all 3. Could it be as simple as the plugs are fouled? I'll find out this weekend and let you know.
On a side note;
What are the chances of all 3 coils going bad at the same time? What about the rectifier or stator going bad? That would effectively reduce charge to the coils and thus kill my spark(I think). I'm more of an automotive guy this is my first boat and two stroke outboards are something new for me.

Regards,
Rick

Re: Loss of Power After Engine Warms

Rick Thomas said:

Jones,
Hey Bud thanks I was thinking of replacing the spark plugs. I don't know when they were replaced last and is a really cheap fix. I was just looking at the price of the coils thats $150 drop right off the top if I get all 3. Could it be as simple as the plugs are fouled? I'll find out this weekend and let you know.
On a side note;
What are the chances of all 3 coils going bad at the same time? What about the rectifier or stator going bad? That would effectively reduce charge to the coils and thus kill my spark(I think). I'm more of an automotive guy this is my first boat and two stroke outboards are something new for me.

Regards,
Rick

Click to expand...

You're thinking along the right lines though, odds are all the coils don't drop dead on the same day, common denominators are more likely , so look at stator , powerpack if it has one. Any elec component can get balky as the engine heats up, rectifier if it has one.

It could also still be fuel delivery, thats why I say spark gap test to seperate fuel from ignition problem. You can also try pumping the fuel bulb on the fuel feed line from the tank, see if the rpm picks up.

you can also check compression, could need a decarbing with seafoam, sometimes a ring will stick.

Also try spraying fuel into each carb throat when it will not rev up.

Something will cause it to react and point the way.

2 strokes are simpler but ...different.

Re: Loss of Power After Engine Warms

Jones,
I finally got a hold of the shop and talked to the mechanic there. We talked about the issue you need to follow the same principal as a car engine. Spark, Fuel, Compression. I asked about throwing a garden hose on it and he told me no point I gotta trailer it out and find out what cylinder it is under load. Being its a 3 cylinder its pretty easy. He thinks if I can't pin it to a cylinder I am having issues with the powerpack. They commonly start acting up after the engine warms.

To answer your question the bulb is as hard as a rock when it does this. I already popped the fuel line off and cleared it out and plugged it back in, same thing.

Side note:
1973 65HP Johnsons are odd ball motors with reversed gearing. They only did this for 2 years. Anyone know why?
Regards,
Rick

Re: Loss of Power After Engine Warms

Maybe they had a warehouse full of counter-rotating gear sets to get rid of.
My 150hp is a counter rotator.

You can test the PP output with a peak reading meter, but it still usually turns out to be the PP. Marine peak reading meters for outboards can be found on ebay for $60 most days.

Re: Loss of Power After Engine Warms

Jones,
To recap.
Pull the plug wires if I find a cylinder that does nothing I hit pay dirt. If I have spark then I have a fuel/carb issue. Here's an after thought. When I popped the cover off this morning I noticed I am only getting half movement of the throttle linkage when I have the control cranked to full throttle. Under cold running conditions I get about 3800-4000RPM (4500-5500RPM max operating range). Does the throttle linkage adjust back after the engine warms? I will post a picture in the morning regarding what I am talking about.

Thanks!
Rick

Re: Loss of Power After Engine Warms

Hey,
I forgot my darn camera at work last night. I'll get those pictures tomorrow.
Rick