1992 Johnson 40HP - No thrust, rough idle and sounds

[oldboat1]

Some chugging and smoking going on, at least.

Would first try it with a new head gasket -- fresh fuel, and check fuel supply for water or other contamination, along with checking temp.

(as an aside, sounds as if the starter bendix is rattling or something similar.)

 

[Vile]

Some chugging and smoking going on, at least.

Would first try it with a new head gasket -- fresh fuel, and check fuel supply for water or other contamination, along with checking temp.

(as an aside, sounds as if the starter bendix is rattling or something similar.)

Would all of that cause lost of thrust?

Motor cranks, but won't catch easy any more. Fuel could be pretty old. Going to flush it and redo the carb cleanout. I did spray seafood in carbs.

Checked compression one last time being a ran it some more. Both cylinders still close to 120.

How hard is replacing a head gasket for a novice? I do see the bolts to pull the head. Doesn't look that complex

 

[oldboat1]

Would all of that cause lost of thrust?

Motor cranks, but won't catch easy any more. Fuel could be pretty old. Going to flush it and redo the carb cleanout. I did spray seafood in carbs.

Checked compression one last time being a ran it some more. Both cylinders still close to 120.

How hard is replacing a head gasket for a novice? I do see the bolts to pull the head. Doesn't look that complex

umm. Seafood in the carbs might slow you down, some.

Easy job, and not expensive if you do it yourself.

[Edit. think you might do the fuel cleanup first, and see if you get improvement -- step at a time....]

 

[Vile]

Sorry, was responding via mobile phone. Guess the autocorrect got me.

I called my father. He said he took off the Cylinder Head rather easy within 15 minutes last time. So, I'll bring it over to him as he is also a master machinest too.

He tossed me the model number. I guess it's actually a 92 40 HP motor. ********** has a nice reference page for everything I need with a nice diagram. Looks pretty easy to replace a gasket based on what they show. New head gasket (#20) is listed as $35 bucks.

Question: Would it be worth checking the Water Gasket (#15) too? Looks pretty easy to check and on the other side.

 

[oldboat1]

yeah, need autocorrect to correct autocorrect. Sound like you are on track. When you guys pull the head, I would clean it out some (salt corrosion -- think your are in salty or brackish). Think it's a good idea to go after the water passage cover and gasket too, for the same reasons. Might as well clean it out.

 

[Vile]

Only freshwater here. If you referenced the video, I'm on Lake Gaston, North Carolina side.

 

[oldboat1]

Ah. Pretty area (nice video shot).

 

[Vile]

Long time, no update.

I finally got the boat out the water and back at the house. I was also finally able to do a spark test with new plugs. Spark looks good on both plugs and the boat fires right up. Unfortunately, it still sounds deep, still has a slight knocking sound and still sounds like low thrust.

We have not pulled the head yet, but looking to any additional thoughts on the issue here outside of possible head gasket issues. Compression is still good in both cylinders.

 

[Bosunsmate]

slight knocking...
check flywheel for play
check timing- broken flywheel key can cause low power and knocking.
You can also drop the Lu and run it with hose attached, check if the sound goes away.
If not check big and wrist pin bearings by pushing on piston at tdc

 

[Silvertip]

Carburetors need to be removed, disassembled, cleaned and reassembled using new kits. Spraying stuff in the throat does nothing. In your first post you said the engine died because of bad battery cable connections. That was not the cause -- once the engine is running it will continue to run if the battery is removed because you have a magneto ignition/battery start. Not a battery ignition.