My 150 johnson is bogging down for some reason. A month ago I noticed that when I began to pick up speed it would lose power and bog down from 50 mph to about 35mph. Last week-end I had a hard time planing the surface. Could it be my spark plugs or the wiring to the plugs? I cleaned out the gas tank and the plugs are only 5 months old. The year of the engine is 1987, but I pretty much had everything replaced, such as the stator, starter, rectifier, and main engine harness. I know one of the cylinders is losing compression, but would that be the cause of it losing so much power. I noticed that the Rpms would only go to about 4000. Any suggestions?

If it has the VRO (and it's not been disconnected yet), then that's the culprit...!

When it bogged down did u push the choke in and see if it regains speed.If it does the carbs are not getting enough fuel.Clean em good blow the jets out with a air hose , or run a thin wire thru em.May be the plugs also did u gap them correctly.

It does have a VRO pump, but why would that be a problem?

James..I THINK the feeling is, if your VRO gets weak, it could pump more oil than gas,or mixing them together, deluding the gas causing a lose of power. Have you noticed more than usual smoking ? I would also look at the gas return valves on the carbs. I had them ( some) stop up, causing this type problem.. I no mechanic, so take this as just guessing..

Well really you answer your own question you say you say you have low compression in a cylinder and more than likly the reason it bogs down is that the engine is trying to sieze up the more you run it, the more damage you will cause so I would suggest having it look at. When you lose a cylinder you will lose around 750 to 1000 RPM.......OPTI

James Jr.

Follow Opti's advice. He is a full time master mechanic.

If you know you had a bad cylinder several months ago, recheck the compression on it. I would be very surprised if it is still as high as it was the last time you checked it.

The longer you run it, the more $$$ it will take to rebuild it later on.

So take Opti's advice and have it looked at.

If i have bad compression in one cylinder, do I need to replace the entire powerhead

No sir if you only have one bad cyl they can repair that one hole and hone and re-ring the rest of the cyls and make sure they find the cause of the failure or it will happen again only reason you would have to replace the powerhead is if the block was not repairable....OPTI

How much do think it would cost for a 1987, 150 Johnson GT to have a cylinder replaced? I think the guy I took it to is trying to empty my wallet. He said the compression in one of my cylinders is extremely low and that he would have to replace the entire powerhead which would cost me over $2000 overhaul. I really appreciate your help. Right now I pulled the spark plugs and cleaned them off. The side with the bad cylinder was pretty grimey. The other side was clean. I pulled the fuel tank and I am letting it dry out. I replaced some old fuel hoses. The wiring to the plugs looks pretty old. I have already had the stator, rectifier, starter and main engine harness replaced. The plugs are only 6 months old. I remember when the mechanic opened up the cylinders and the one cylinder that was bad seemed dry and white. I have put a lot of $$$ into this engine, I want to keep it running as long as I can. This is my first boat and it has been a bad experience. I decided to get an older boat over a new one just because I wanted to learn everything I could before buying that 40,000 dollar boat. So far I have learned a ton, but my wife is about to kill with all the heart-ache this Johnson has caused me. I have won a few tourneys out of it but I don't think I'll ever break even. Anyhow, thanks for your time and great advice. James

If you have a bad cylinder $2500 is a typical price to fix it..........and you dont have to spend $40000 on a boat..........just find one that's 1-2 years old with a motor with a known history and have a mechanic check out the boat and motor BEFORE you buy it.

My Wellcraft was a little over one year old when I bought it 9 years ago! .........and I saved over $14,000 on the price vs a new model.

I have the same problem on a 115 horse Johnson. I was looking at prices on pistons and they are around 87 bucks a piece including rings. Ring sets for the good cylinders run 20 bucks a cylinder. Cost is going to depend on the damage done. If it's not real bad you might get by cheap with just honing it out. One thing I was looking at since I would have everything apart is to go ahead and slap new bearings in the motor. Spend a little now save alot later. Save even more if you can do the work yourself.

Boatman1
If a cylinder is $87 dollars and ring sets for the other 5 cylinders are $20 a piece that comes to $187. Why would it cost $2500 to replace one cylinder?

Labor at a shop to do it most likely. Up here it's like 80+ bucks an hour for general labor. I am sure it's like the automotive side where there is a set rate for certain work. My V4 was going to be around 500-700 on parts to rebuild myself. Thats all the gaskets, bearings, rings you name it. Depending on cylinder wall damage you may have to take it to a shop for boring the cylinders. One thing though a shop can probably get it done and have you on the water quicker and with a lot less headaches of retuning. Just a matter of time, money and skill.