100 Johnson isnt running correctly. Help!

[mkeleher]

Im new to this website and fairly new with working on boat motors so any help is greatly appreciated. I recently boat a stratos boat with 89 johnson motor. 100 hp model j100stlcem. The first problem I had but didnt know was the ignition switch. Not knowing that was the problem at first I cleaned out the carbs to the best of my knowledge. Then I realized the fuel pump wasnt getting power and pumping fuel when I turned the key. So I replaced the ignition switch. I fired it up in the driveway and fuel pump worked good. Everything seemed to be working right. Smoked a lot but thought it was normal. Next brought it to the lake to see how she ran. Here's where the problem comes in. I pushed the throttle all the way down to take off and it only runs 2000rpms- 2500rpms. After letting it run like that going about 8 mph it decided it wanted to run good and just took off like nothing was wrong to 4000RPM's. Ran great at 35 MPH until I let off the throttle to see if the problem was gone. Did the same thing for about 5 minutes then took off again to 35mph. There are a couple of questions I have. Did I wire the ignition switch wrong? Did I reassemble the carbs wrong? Is the gas : oil wrong? Could there be a clog in gas lines? Or is it something small I am doing wrong? The motor wants to run so bad but just cant stay consistant.PLEASE HELP!!!!!!!!!

 

[andrewddrennon]

Re: 100 Johnson isnt running correctly. Help!

To the best of my knowledge that motor doesnt have an electric fuel pump. Is that why you thought you needed to replace the keyswitch? Anyway are you pumping up the primer bulb before you take off? If so check to see if its solid when the problem occurs. Sounds to me like a primer bulb or maybe a gas tank vent.

 

[F_R]

Re: 100 Johnson isnt running correctly. Help!

mke, you guessed what the problem was and it didn't work out too well. Now, if we guess, it may not work out too well either. It is pretty obvious that the motor is not running on all cylinders. When the missing cylinders kick in and start firing, it takes off and runs fine.

The problem at hand is figuring out why. You must start out with an orderly and sensible troubleshooting system. Compression is probably ok, since it CAN run ok, but that still is always the first thing to check before running off in ten different directions. Second thing to check is spark. Will it produce a 1/2" spark with ease, on all cylinders? Related, but often ignored is spark plugs. Doesn't make much sense to rebuild the whole motor when all it needed was a spark plug.

Ok, two things down and two to go. Is it getting water into a cylinder or two? You should have already detected that during the first two checks. Finally, the one that everybody wants to blame---maybe rightly or wrongly. The fuel system. You say you cleaned out the carburetors to the best of your knowledge. What does that mean? Were they dirty? Maybe you didn't get them clean. There are two two-barrel carburetors, which amount to four carburetors, all with separate jets. If any one is dirty, the associated cylinder won't get proper fuel mixture.

Lastly the fuel delivery to the carburetors, meaning the fuel pump and everything between there and the fuel level in the tank. Actually, including the fuel itself, in that tank.

So there you go. You know what you have to do. We can't do it for you. You must diagnose the problem BEFORE you fix anything. Chances are, it will jump right out at you, like if it doesn't have 1/2" spark on all four.