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Rebuilt 140 hp wet plug problum, not enough power.

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old55pete

New member
Let me start out by saying that I am a diesel truck and equipment mechanic, I also build my own race car engines. That being said, I was asked to rebuild a 140 hp Johnson outboard engine as it 2 seized pistions, had low compression in #1 and none in #3 .had the block boared .30 over. new pistions, all new bearings. even rebuilt the carbs. Starts good, ran a break in in a barrel yesterday then to day put it in the lake. It dident have enough power to get it up on plane. Adjusted the timming some and it got better, changed the plugs and they came out wet. Put in another set of plugs and that made it worse, Put in a new set of plug and it would come up on plane but took forever. About full minute, then rpm would run up to 4500 wide open and have no throtal left . Pulled a compression test, we have 120 lbs all around . Any ideas will help
 
Model is 140TL79R. We checked the carb sync several times and look to be opening at the same time all the way to WOT. It is on the same boat it came on, Second owner.. There a no idle mixure screws that I could find. So I have to say fixed. The hull is clean and smooth and the owner knew about the trims settings and has owned it for 25 years. When we pulled it out of the water, we got about a gallon of water out of the bilge, this was the first time on the water in several months. I set the floats by the book,turn carb upside down and set to gasket rim. 50 to 1 premix. There were no electrodes on the spark plugs to adjust.
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How do you do a cylinder drop test? A cylinder cut out test? Pull a wire off a plug while it is running and see if the RPM drops or not. The reason that I am asking is that this engine has elotronic ignition, but is to old to plug in any kind of scan tool.
 
Because we went through the whole engine and knowing that a lean carb can cause it to seaze a piston, we replaced the fuel pump. I will have to look for the marks on the linkage and see it they are lined up. I used an inline spark tester and each cylinder had a hard blue/ orange spark. The first time I changed them they were all soaking wet, the second time they were so wet, it was a wonder they were fireing. the third set were only damp
 
Are pistons installed correctly as it will start and run but wont have enough power to pull a greased string out of a cats arse? And yes the domes will clear head if they not the high compression heads....
 
How would I tell if the pistons are in backwards? I was carefull to mark each one and re assembled them the way they came apart, but that dosent mean I did it right. As far as I can tell, I am not the first one into this engine as it had two .10 over pistons in #1 and #3 and could have been installed wrong then.
 
Fazbullet, That's it, they are in 180 out. I looked at the pictures that we took while we were taking it apart and I have them in the way they came out. Guess they were installed wrong the last time also. I have the factory service manual coming so I can get the proper carb/timing sync set up and check out a few other things that have me baffeled . I guess I will have to stick with what I know. Thank you sir
 
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