Late 80's 110H.P. Johnson Idle only

[Spunbearing]

A friend bought a boat with a late 80's 110hp johnson on it, probably in satwater most of its life from the looks of the corrosion, had the carbs rebuilt at a shop, took it out on the water today and it ran pretty well for about an hour or so, it did have some intermittent issues of losing power at rpm, was on a plane for a while engine at 5700rpm and it seemed to lose power a little bit a couple of times like it had earlier then in just died, got it to start but it would only idle and die if you gave it more throttle, had to idle all the back in a couple of miles, pulled it out of the water and it would rev but had some pretty bad misses. I think its probably ignition, any help would be appreciated. I'm pretty familiar with motors but rather new to marine stuff.

 

[Daviet]

Re: Late 80's 110H.P. Johnson Idle only

Well start with a compression and spark test.
Spark should jump a 7/16" air gap and be bright blue.
Compression should be somewhere around 115-125, higher would be great, but mostly they should be within 10% of each other.
If those check out OK, move on to the fuel system.

 

[Spunbearing]

Re: Late 80's 110H.P. Johnson Idle only

This has to be common and I'm pretty sure it not mechanical or feul, it ran too well, I'm thinking power packs. Anybody wrench these full time?

 

[emdsapmgr]

Re: Late 80's 110H.P. Johnson Idle only

Weak electrical components tend to fail when the engine heats up to normal operating temps. Run the engine on the garden hose on the trailer. Make sure the engine is fully warmed up. Use some insulated pliers to pull one spark plug lead off one plug. The engine idle rpm's should drop noticeably on the tach. Try the next spark plug wire, etc. If you pull one wire off and the rpm's don't drop, that cyl may not be firing. You can confirm this with an inductive timing light on each plugwire.

 

[Boss Hawg]

Re: Late 80's 110H.P. Johnson Idle only

Agree- When I first put my 86 110hp Johnson in the water it did about the same thing-
Tryed all the hard stuff first- Found one bad plug wire about the time i wanted to give up :facepalm: