'89 johnson 120 surging from 4k-3k

[mookieo2]

Ive been trying to get this engine going for a while and gave up for a year. When I originally got it it needed a power pack and rebuilt the carbs, primer ball, disconnected vro ( because my old engine was premix), new plugs, etc. It started and ran great up until 2k RPM's. It wasn't overheating and I disconnected the slow feature. A little research and it seemed like maybe it was the fuel pump.

Last fall I rebuilt the fuel pump with the omc kit( I know it usually doesn't work but figured I'd try that first before spending $300 on a new one) rebuilt the carbs again, wet sanded the warped bowls flat and set the floats, reinstalled the fuel hoses with new tie wraps( not the cheap home depot ones) it ran but I couldn't test it due to the steering cable being frozen. I also did a link and sync, and tested the electrical system with a peak voltage tester according to the manual. Everything checked out OK.

Just put it in the water for the first time after that and it ran a lot better. I could get it up to 5k and it would run, not stall, idle fine. When cruising I could get it to 4k and then it would bounce back and fourth from 4k to 3k RPM's. It never stalled and would idle fine where before it would just run great until 2k then die.

Any ideas besides an air leak in the fuel system. That's what I came up with first in my searches after I got home.

 

[71Windsor]

Re: '89 johnson 120 surging from 4k-3k

Well disabling the slow feature wouldn't help you here slow would kick the engine down to a crawl so you can eliminate that. First thing that comes to mind is fuel. Check your pulse line from the crank case to the pump

 

[mookieo2]

Re: '89 johnson 120 surging from 4k-3k

Well disabling the slow feature wouldn't help you here slow would kick the engine down to a crawl so you can eliminate that. First thing that comes to mind is fuel. Check your pulse line from the crank case to the pump

The pulse limited was the only thing I didn't check. I'll try to look in there when I check the fuel lines again.

The slow is connected. I disconnected it when I was testing it last year when it wouldn't rev passed 2k. It is connected and the power pack was spot on when I tested it according to the CDI test procedure.

 

[Bosunsmate]

Re: '89 johnson 120 surging from 4k-3k

Does it sit on 5k fine? does the problem only happen at 4k?
Any un-eveness in the colour of the new plugs?

 

[mookieo2]

Finally had some time to check it out again.

Re: '89 johnson 120 surging from 4k-3k

Does it sit on 5k fine? does the problem only happen at 4k?
Any un-eveness in the colour of the new plugs?

same thing at 5k too.
Checked the plugs and they looked good after I ran it around the last time, not black and a little wet with fuel. all the same color.


Squeezed the fuel ball until it was firm and then a little more. No fuel was leaking and the ball remained firm.
Checked the fuel lines and replaced a few tie wraps with factory clamps. (the bigger lines)
Removed the pulse limiter and cleaned with carb cleaner. It wasn't clogged or anything. I could blow through it lightly. It was brass with black plastic on the front part where the hose attaches too.( not sure if that is the up to date one or not)
Brought it back to the water and it ran like crap. Wouldn't stay running. Had to hold the choke in to keep it running. Had the carb cover removed to check the carbs for fuel, etc. ( not sure if that is what caused it to run like crap)
Fuel ball was firm the whole time.
Started sneezing a little when I got it to run on its own
brought it home. Plugs were black and dry with sooot. (probably from holding the choke)
Compression was 120 on 2 cylinders, 117,and 122 on the other 2.
Checked spark with tester, all coils fired strong.


Don't know what it could be. I can't figure it out.:mad-new:

 

[mookieo2]

Disregard my last post. Forgot the air box cover has to be on. Saw some fuel by the carbs. I believe the problem is warped carb bowls. I had sanded them down a little last year but not that much. Took them apart and wet sanded on a piece of glass with 600. Thought I had them pretty good but when I put them back and pumped the ball I could see a very slight amount of fuel weeping from the front by the gasket. They all have new gaskets as they were rebuilt a year ago when I first started to try to get this motor going. I guess I'll try to sand them down a little more and test them again. Can you still buy these bowls? Evinrude site and a few others says obsolete. Since I believe problem is an air leak in the fuel system this seems like it should be the problem. Then boat ran great except for the surging.