85 hp johnson, one cylinder down

[swmpman]

I have a 24 foot pontoon with a '78 johnson, 85hp. One cylinder is not working. My quesiton is would it be worth the money to fix this motor or just get a bigger motor. I do not know how much this one cylinder affects the top speed of the boat. I only get about 15mph on my GPS. If I fix this cylinder will it help much with my speed or should I get a bigger motor. I am a newbie so please be gentle. LOL

 

[P 0 P E Y E]

Re: 85 hp johnson, one cylinder down

Down can mean different things

Is it a compression problem? - if it is, it was, and you been running the motor and making things worse.

Is it a fuel problem to that one cylinder, that lead to a compression problem, that you have still been running the boat and causing exponential wear?

Is a coil bad, or is there lack of spark to one cylinder, this could be not as bad because you were still getting lubrication to the bad cylinder.

The question is what is the exact nature of your loss of power?
You may need to perform some basic troubleshooting to find out what the problem is or is not.

Heck you may have knocked off the plug wire when you put the engine cover on. Take a look at the engine.

Oh, Welcome to the forum, Sorry about my bad breath, lack of shave and sailor attire

 

[clint]

85 hp johnson, one cylinder down

First you have to see what Horsepower your Boat is rated at? Probably you can use up to 100 HP. There should be a tag, sticker. What year is the engine? Your looking at $1500.00 to $2000.00 for a normal Re-build. I would suggest a rebuild if motor is under 10 years old. You are working with a 31 year old Engine? Remember a brand new outboard in your HP range is at least $10,000. Try to find a good Used motor or newly Re-built that you can probably get for under $3,000. Rebuilt & ready to go. Good Luck!

 

[swmpman]

Re: 85 hp johnson, one cylinder down

Sorry about the lack of information. I am pretty sure that it is a fuel problem. I did check the compression and they are all pretty close around 110. My main concern though is the speed. I know there are several variables to consider on how fast it will go but I would like to see more speed than I am getting. If it will not help much to fix that cylinder then I will just try to get a larger motor and sell this one. Does anybody know what kind of speed I can expect out of a 24 foot partybarge with an 85hp motor? Again, I know you can't be exact but a good estimate would help.

 

[R.Johnson]

Re: 85 hp johnson, one cylinder down

You simply cannot run that engine with one cylinder down without damage. One way or another, it's going to get worse. How long will it take before it comes to a total stop? That's anyone's quess.

 

[emdsapmgr]

Re: 85 hp johnson, one cylinder down

Soungs like the compression is ok. If the engine has good compression, it is worth spending the time to get it running on all 4 cylinders. If you get the engine running well, you may get the speed up to around 20 with a light load. Your older engine is hp rated at the crankshaft. Today's engines are all hp rated at the prop, so your engine produces less hp than today's equvalent 85 hp. Around 10-12% less. Pontoon boats respond to hp increases differently than normal planing boats. If you went with a newer 100 hp engine you would only pickup maybe 5 mph in speed.

 

[aclmvh]

Re: 85 hp johnson, one cylinder down

You say one cylinder is not working, but I haven't heard you state what the problem with that one cylinder is or why you think it is not working, other than the speed of the boat...the cause of which could be many different things not related to the motor. You have good and matched compression in all four holes, so it would seem its not mechanical. Why do you think one cylinder is bad? Have you checked fuel and spark to the cylinder?