1998 johnson 3 cylinder 35 hp

[JoshKeller84]

hi guys, just bought this engine for cheap. compression is even at 120 psi on all 3. good blue spark that jumps 1/2" on all 3. cleaned the carbs. pump the bulb, and the carbs leak from the overflow if i really pump hard. the carbs do not leak when the motor is running. I put the motor in a barrel, and started it up. it ran extremely smooth and was so quiet i could hear the tell tale water stream hitting the black top. now for the puzzling part - i put my hand over the carbs individually to make sure it was firing on all 3 cylinder - the bottom one cut out immediately, middle one took a few instances longer, top one a bit more than the middle one. would this motor idle so smoothly if it wasnt running properly on all 3 cylinders?

let it idle in the barrel for 20 minutes, until i unknowingly let the tank run out of gas. put another gallon in, pumped the bulb firm, and it was a bear to start - must have taken 50 pulls. I disabled the oil mixer by removing the tank, and putting a bolt in the oil line. the mixer itself is still hooked up, but i run pre mix - do i need to remove the mixer and just allow the two front mounted fuel pumps to deliver the fuel? sorry for so many questions, this is my first loop charged motor.

 

[jbjennings]

Re: 1998 johnson 3 cylinder 35 hp

I can only help with a couple of questions because I'm not at all familiar with the 3-cylinder 25's.
1) yes, they can idle suprisingly smoothly on 2 of 3 cylinders.
2) I would definitely do some research to find out the proper way to remove the oil injection system if you intend to run premix. Some of those systems involve more than just removing the pump and putting on a blockoff plate.
3) Usually a motor being really hard to restart when warm is because it's flooded. Maybe If that oil pump is pumping, you may have too much oil going somewhere that it shouldn't.
What do your plugs look like after you ran it a while?

I hear the powerpacks give a lot of trouble on those 3-cylinder OMC's.

 

[hidef]

Re: 1998 johnson 3 cylinder 35 hp

Remove the mixing chamber you don't need it. Connect the fuel line running from the mixing chamber to the carburetors directly to the fuel filter that is between the fuel pumps and the mixing chamber. Secure the wiring connector that went to the tank sending unit out of the way. You would know if the engine wasn't firing on one of the cylinders as these engine are very smooth. When they start missing it is very pronounced. There check valves in the mixing chamber which could have prevented fuel from going to the carbs and why it was hard starting.

I suggest you get the BRP / OMC factory service manual if you are going to keep the engine. It will remove a lot of the guess work while working on the engine.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

What is the correct way to verify it is idling on all three cylinders?

 

[boobie]

Re: 1998 johnson 3 cylinder 35 hp

Pull one spark plug wire at a time and see if you get a cyl drop. And get rid of that oiling system on it and mix your fuel 50:1.

 

[kfa4303]

Re: 1998 johnson 3 cylinder 35 hp

+1. However, be sure you use insulated pliers while you do the job, or you'll be in for a heck of a shock

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

solved the fast idle lower cylinder. the screw had stripped threads and wasnt allowing the carb to sit completely against the intake gasket. retapped hole and replaced bolt. slight leak from overflow was fixed by rotating needle valve. temp fix, as i have ordered 3 overhaul carb kits. motor idles so smooth and quiet you can literally hear the tell tale hitting the pavement over the motor. control cables should be in today, so hopefully it runs at wot as well as it does at idle!

 

[Daviet]

Re: 1998 johnson 3 cylinder 35 hp

Glad you found your problem.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

took it out for a spin - would not plane boat out. put it back on trailer and headed home. fire motor up on hose, and unhooked all linkages. pushing the butterflies on each cylinder, the top two immediately responded, the bottom one bogged down for several seconds before slowly picking up. could definitly smell gas, and spark plug appeared to be wet. im assuming the needle float is still not sealing completely and flooding the bottom carb. sound correct? i have a video of this test i am trying to upload to youtube

just to be sure, i rechecked compression 127, 129, 127. reed valves looked good when i had all the carbs off. getting great spark that jumps 3/4"

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

https://www.youtube.com/watch?v=GvZfZVP5V2c&feature=youtube_gdata_player

 

[daselbee]

Re: 1998 johnson 3 cylinder 35 hp

Well, I don't know exactly what's wrong with your motor, but I had one once that had great compression, but would not idle. I checked idle timing and found it to be about 6 deg BTDC., just to get it to idle at all. Crappy and no power. So, I pulled the head, and measured the bores. Way out of spec. Sorry I cannot remember the exact details, but it was a case of very out of round, and tapered cylinders. Might want to check it out.

 

[daselbee]

Re: 1998 johnson 3 cylinder 35 hp

Notice I said BTDC!!!!! Not ATDC. Way wrong to make a good idle. Remembering more, I could use one finger to rotate the crank at the flywheel. No resistance at all, but still 120 psi when cranking at starter speed. Very weird.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

just to help with the diagnosis, i swapped the top and bottom carb, and the problem followed to the top cylinder.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

sorry for the big picture, but here is the fuel pooling up in the top carb (formerly the bottom) and dripping down onto the others. the problem definitly followed when i swapped carbs, so i've isolated it to a carb problem. im still in belief in the needle not seating properly, but will the pooled up fuel cause the cylinder to not run at all thats attatched to this particular carb?

 

[kfa4303]

Re: 1998 johnson 3 cylinder 35 hp

HI josh. I agree that the flooding is probably due to a stuck float needle as well. I guess you'll have to take the carb apart to inspect it fully.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

i've determined that the float valve is worn and not sealing 100%. by blowing on the fuel line hook up and turning the carb upside down, it still allows a slight amount of air in. would the flooded carb not work at idle or wot?

 

[kfa4303]

Re: 1998 johnson 3 cylinder 35 hp

A flooded carb will not work very well, if at all, at idle because it would cause too much fuel to be mixed with the air, thus inhibiting ideal combustion. Many old motors were designed to be killed simply by retarding the timing/spark, creating a very rich environment which would cause the motor to stall and die. It seems a little counter-intuitive, but gasoline really only burns well in a gaseous, or atomized form. If it's too liquid it won't burn very efficiently. While at WOT the motor is consuming more fuel and may be able to keep up with the excess fuel delivery a bit better, however it would still be less than ideal, preventing the motor from reaching max rpm while expelling large amounts of unburnt fuel along with the exhaust gasses.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

i certainly believe this to be the case. the problem is definitly carb related, and there was a fuel slick behind the boat. fuel is pooling fairly deeply into the carb throat. ordered a new float valve/seat and it will be here wednesday. is the correct idle sync procedure to simply set all butterflies to the closed, and set so all 3 are openeing and closing at the same rate/sequence?

thanks guys

A flooded carb will not work very well, if at all, at idle because it would cause too much fuel to be mixed with the air, thus inhibiting ideal combustion. Many old motors were designed to be killed simply by retarding the timing/spark, creating a very rich environment which would cause the motor to stall and die. It seems a little counter-intuitive, but gasoline really only burns well in a gaseous, or atomized form. If it's too liquid it won't burn very efficiently. While at WOT the motor is consuming more fuel and may be able to keep up with the excess fuel delivery a bit better, however it would still be less than ideal, preventing the motor from reaching max rpm while expelling large amounts of unburnt fuel along with the exhaust gasses.

 

[JoshKeller84]

Re: 1998 johnson 3 cylinder 35 hp

Got the Carb fixed and it idles great. However the motor still won't open up. Verified it not being a fuel problem by spray gas and oil mix into the carbs and no change. Figured I had nothing to lose so I ran it on the water hose - still won't open up there either. Pumped primer bulb while running and made no difference. Here is in the water video and one on hose. Any ideas?


https://www.youtube.com/watch?v=EwIiE4rHyN8&feature=youtube_gdata_player


https://www.youtube.com/watch?v=8c28Znn-6Wc&feature=youtube_gdata_player

 

[Daviet]

Re: 1998 johnson 3 cylinder 35 hp

Use an inductive timing light and check each plug wire under load and see if you have a constant flicker on each wire.