1999 Johnson 150 Bogs when warm

[MMcrack]

Good morning all! I'll try to keep this as short and to the point as possible while still getting my point across...
I've got a 1999 Johnson 150 that's not given Mr any problems until this season...for some reason when the engine is warm it won't get past 1500 RPM without bogging down and trying to die.
Here's what I've done so far:
-pulled apart and cleaned all carbs and verified bowls weren't warped.
-had a spare VRO rebuild kit sitting around so I changed that.
-pulled apart the vapor separator and made sure the float was set properly.
-my powerpack was acting up last year so I replaced that, cables, optical sensor, and plugs. (Started this season with my old PP, cables, optical sensor, and plugs and it was still doing the same thing)
-verified good compression.
-replaced fuel lines, water separator, etc.
-tested with external fuel tank and new fuel.
-replaced water pump at beginning of season.

I will fess up and say that I have not checked timing and I didn't take apart the vapor separator pump to verify the diaphragm was still good.
I believe it's fuel related simply because I leave the ramp perfectly fine, but once the engine is warmed up the only way for me to get above 1500 RPM and get on plane is for me to play with the throttle and choke. Once it's warm and I come down from being on plane if I sit at idle it'll start to sneeze like it's running lean.
Has anyone ran into this problem or can guide me in a direction to keep troubleshooting it before I burn this beast to the ground?

 

[Chris1956]

Does this only happen when you have run it and then stopped to fish or swim for an hour or so. Upon restart it runs poorly and wants to stall. Is that it?

I am not sure of the fix. I would recommend you put in new thermostats, as it may have heat soak. Also, run it for a minute in neutral after you stop, to cool it off.

The mitigation is to restart it and run it at 1200 RPM in neutral for a couple of minutes until it starts to run normally.

 

[MMcrack]

Does this only happen when you have run it and then stopped to fish or swim for an hour or so. Upon restart it runs poorly and wants to stall. Is that it?

I am not sure of the fix. I would recommend you put in new thermostats, as it may have heat soak. Also, run it for a minute in neutral after you stop, to cool it off.

The mitigation is to restart it and run it at 1200 RPM in neutral for a couple of minutes until it starts to run normally.

The shortest time I've noticed it happen was about 5 minutes or so on plane from the ramp and then I had to go thru a no wake zone. On the other side of that It died on me. I've briefly found out that if I keep it above 2000 RPM than it'll get back up there without having to play with the choke. Sadly I only got to try this twice before a big storm rolled in.
I'll look more into this heat soak issue and try the 1200 RPM the next time I'm out. I always allow it to cool off before turning it off same as I do my diesel and any other engine.
I thought about the thermostats over the weekend and wanted to pull them out just to see if anything was gunked up in there, but was unable to get either of the caps off before I thought they were going to break. I haven't changed them in the 3 years I've had the boat so maybe that should be changed anyways? But my pee-tale is STRONG.

 

[Chris1956]

Thermostat covers are plastic, right? They should not corrode into the block. I broke one of the small hex heads on the cover, but the larger one removed the cover.

 

[Chris1956]

Strength of the telltale stream makes no difference. If the thermostats stick closed or don't open enough or soon enough, motor will get hotter than designed, possibly leading to heatstroke.

 

[MMcrack]

Thermostat covers are plastic, right? They should not corrode into the block. I broke one of the small hex heads on the cover, but the larger one removed the cover.

They are plastic. My thing is I don't know what the previous owner did i.e. glued them in there or something is what it feels like. Haha. I'll take a look at them tomorrow if all this rain stops and I can work on it.
And, I didn't know that about the thermostats. I surely hope it's something as simple as that. But hopefully some others will still chime in if they know of any other things

 

[MMcrack]

Strength of the telltale stream makes no difference. If the thermostats stick closed or don't open enough or soon enough, motor will get hotter than designed, possibly leading to heatstroke.

This past weekend I was able to replace the thermostats. One of them had a piece of silicone in the end of it. Both were dark brown and obviously needed replacing. I took it out after and it did the same thing though. But here's the kicker...when I get it up to right around 3000 RPM I start to hear a knock now. Because I was already on the water I decided to do a little more troubleshooting. My buddy let me borrow a fuel pump that he converted his VRO system to. It's one that bypasses the oil system completely so I took my spare tank with me that had 50:1 in it. Same result.
Still while on the water and frustrated as I could be I decided to take the vapor pump diaphragm off since I haven't taken it apart yet. Once I got it all back together and the stupid hose next to the carb reattached I tried it again... it's better....not fully, but better nonetheless.
So now when I give it balls to the wall power from idle it will still die. But, if I get it up to ~1500 and play with the throttle than it will rocket up to 3000. Oh, and the knocking is still there.. W.T.F. IS GOING ON?!

 

[oldboat1]

Do some basic tests if you haven't done so yet. Get an infrared tester and measure the temp at the top of the heads. Around 140F would be normal. 160 or over is definitely overheating.

 

[MMcrack]

I'll definitely try that out. Would the temps be different while on muffs vs in the water?

 

[oldboat1]

Could be. Can't do a whole lot of testing on muffs. The incoming water is about 40 degrees (F), so that would probably yield slightly cooler running than in an 80 degree lake. But since the hose pressure is pushing the water up, can't tell much about the function of the water pump. A compromise is to run in a large barrel (think plastic trash barrel) with water about half way up the leg of the motor, well above the water pump. Leave the hose running into the barrel to keep the water from overheating due to the motor exhaust. Idle only, assuming you can find a barrel to fit the lower unit.

 

[MMcrack]

Haha yeah I've done the barrel method before. I have 2 old Rubbermaid tubs that I put inside of each other to make it more rigid once the water is in there. I'm working on getting an IBC tote to turn into my own test tank so I don't have to go all the way to the river for these things. Thanks for the input again. I'll get the infrared thermometer and check out the heads this week and let everyone know how it goes

 

[oldboat1]

Creative fixes!! Good boating to you.