1983 Johnson 115 v4

I recently purchased a 1987 Larson 17 foot runabout with a 1983 Johnson v4 115.  This is my first boat. I’m in love with the classic boat but my issue is it will not go over 8 mph. I have found a bad coil which I replaced. New prop. Compression reads 103,105,110,114. I ran a whole can of sea foam in 1 gallon of gas which helped the idle a lot. Idles great and runs like a raped ape on muffs. Once placed in the water it won’t get out of its own way. Will rev high with the idle control but once it’s in gear it will not idle up much at all. The tach does not work but I would take a guess as to it will not rev past 1500 or 2000 rpm. I get 7-8 mph wether alone or with the family. Nothing more. I’m at a loss as to where to look next. Any help would be much appreciated.  

I think Harley joined Lake-link just to get advice lol

He probably got it fixed, we may never hear how the story ended!

Lots of good theories, I’m certainly interested in hearing how it ended...

Daddy always said check the obvious. Did you put on a new fuel line? I had an Evinrude of that era that had fuel issues. It ran like a streak of schlitz until it didn't. Fuel line had a pin hole. New line....Vroom, Vroom! Good luck!

The suspense is killin me.....

Any update Harley?

When a power pack fails it’s easy to find/replace. 

But how do you troubleshoot it when it’s working? 

Good advice CH!

The power pack is a tricky one, as it will work one minute, stop working for 10 minutes, and then start working again. 

I had a power pack intermittently fail on me, and it took me 3-months to figure out!  I’d test it and it worked in the driveway, but failed intermittently at WOT on the lake.

They can be a pistol to figure out!

It’s almost worth throwing 100 bucks at it, especially if it’s 20+ years old! 

Edit: I agree with CH, I wouldn’t play with the carbs yet, I really believe you have a cylinder dropping out.

Thanks BrentHess.  

For Harley.....by pulling each spark plug wire (with insulated pliers or similar)....that will tell you if a cylinder is not firing.  It could be electrical, or it could be fuel/carburator related.  Either way...by pulling the wire will not only tell you if it is an issue....but which cylinder/coil pack/carburator to work on.  

Once you determine if removing plug wires shows anything....I can steer you to the next troubleshooting steps.  I wouldn't remove the carbs and play there yet....it may be your primer bulb or fuel line or fuel filter or fuel pump., etc.....yet.  Since you have spark, then it points to fuel delivery or timing.....but I don't want to jump to conclusions.  

One more thing regarding your power pack, and potentially running on two cylinders. 

The power pack stores voltage from the stator to release it to your ignition coil when the trigger tells it to. Often a faulty Power unit will see intermittent or no spark on cylinders and may only breakdown when your engine warms up.

This is really what I think you have going on here...

I have not been able to try pulling each plug wire individually yet. I did check for spark before I posted and I have a good blue spark on each plug. I will try tonight hopefully to pull each wire as well as pull the carb bowls and clean the jets. Didn’t get home until after dark last night. Hoping I can get out of work at a decent time tonight. Thank you everyone for so much help. I appreciate everyone’s input. 

Also, if you are intermittently running on two cylinders, you may be able to see some signs of that by physically inspecting the spark plugs.

If a cylinder or two is just being dragged along for the ride, the plugs will look very wet and fouled.

I highly doubt your issue is with the lower unit, it is a worm gear of sorts, it really doesn’t slip, and when it does, it sounds bloody awful...

Also, if you do have any gear wear, drain your lower unit, and filter the oil through a paper towel or something similar, if you see lots of metal flakes, you have issues.

I still believe you’re not firing on all cylinders under load, or intermittently losing two cylinders. 

Yeah it’s the lever under the flywheel. 

Harley....confirm that you tried what I suggested initially.  That is the only way to tell if your 4 cylinders are firing.  

What is the timer base?  Is that the lever that moves under what I’m guessing is the flywheel?  That lever moves and changes the idle of the motor. Didn’t get to work on it today. Worked late. Still want to try the carb cleaning and possibly order rebuild kits. 

If your lower unit was bad and slipping the engine should still rev up. Check your timer base to make sure that’s not sticking. I read that the timer base can go out from a busted wire or a bad coil. You did mention it having a bad coil so??