2005 Johnson 90hp carbed 2 stroke J90GLSOB, some trouble-shooting advice please

[SweetD]

Hi Folks,

End of last season I had trouble with my 2005 Johnson 90hp carbed 2 stroke J90GLSOB bogging down/missing when I throttled up past about 2000 RPMs. It started fairly intermittently during the latter part of the season and got progressively worse until finally the boat would not get up on plane at all. Put it away for the season at that point, and now I'm looking into it.

I've done a TON of research/reading/video watching in order to understand possible causes and how to troubleshoot. I have the OEM service manual for my motor and I'm pretty handy, although I've not done a ton of electrical diagnosis in the past - I can however follow directions well. Of course I don't have all of the specialty OMC tools as stated in the service manual, but I do have a good digital multimeter, compression gauge, in-line adjustable spark tester, plenty of hand tools, etc. I also work with very smart and handy mechanical engineers that can help me interpret motor-related issues quite well.

Anyway, I'm trying to start simply and narrow in on my issue(s). I have good even compression within spec across all four cylinders (all over 120psi).

I now want to test spark. As mentioned have the in-line adjustable gap spark tester. My first question has to do with spark testing - I understand how to use the tester tool itself. When I turn over the motor, do I actually look to start the motor on the three cylinders I'm not testing at that time? Or is there a way to turn over the motor without starting it? I can't determine whether the motor is supposed to turn over, but not start, with the kill switch activated. My manual is not real clear on this, plus the manual wants me to be using the multi-plug testing tool, which I don't have.

Second question, different topic: I've noticed my primer solenoid does not seem to be activating when I push the key in. I am hearing no click at the solenoid at all. I know I need to test it and I will - would a bad primer solenoid have anything to do with my bogging/missing condition?

Note: I'll be doing this test on the trailer in the driveway to start on muffs. I know it's better to do testing in the water under load for a lot of issues. After this initial spark test (if it checks out), I will be putting the boat in the water to see whether the symptoms still exist. I've done a visual of the fuel system, fuel lines, etc. I need to check and see whether I have an anti-syphon valve at my fuel pickup. And of course a lot of other possibilities from there...

Any other advice on method / order of operations is appreciated. I understand it could be any number of issues, and possible multiple issues. Please ask for any clarification questions and I will do my very best to answer.

Many thanks in advance - the short boating season up here hangs in the balance!

Dave

 

[jakedaawg]

Spark test done with all plugs out of engine. Use muffs to keep from toasting impeller

 

[SweetD]

Spark test done with all plugs out of engine. Use muffs to keep from toasting impeller

Thanks Jake - so if the plugs are out of the engine, do I have to do anything special with the plug wires that I am not testing? As in, where do I put them if the plugs/wires are out of the engine?

Dave

 

[jakedaawg]

I use a tester that tests all wires at the same time...i think the home gamers with the single spark checker ground out the other leads.

 

[jakedaawg]

 

[SweetD]

Tonight after work i verified that I have spark on all four cylinders. I had a second pair of 20/20 eyes on the tester with my son, and he agreed the spark jumped strongly and blue over 7/16" gap on each cylinder (tested twice each cylinder). I could also hear the motor change when it ran on three out of four cylinders (I ran the motor while testing on the muffs after bringing it up to temp).

I also studied the fuel system as it was running...didn't see any signs of a leak although I can never really tell 100% if the carb air openings are dripping a bit of fuel below, or if the carb bowl gaskets are slightly weeping in a couple of spots. I rebuilt carbs a few years ago after I had a bowl warp (plastic), with all new bowls and innards.

I also could still not hear the primer solenoid click when pushing in the start key, but when I raised the fats idle to about 1500 RPMs and pushed in the key, it choked down the motor significantly. So, not sure about that?

I also took apart the fuel line where it attaches to the tank and confirmed there is no anti-syphon valve in my setup. I took off the sender and fuel cap and looked in the tank a best I could, looked really clean. Cannot get the fuel pickup tube out for inspection though - it's welded into the tank.

I guess next step is to put it in the water, see if the symptoms from last year are still present, and try some of the fuel tests (separate known good tank, etc.), then electrical diagnosis.

One other thing, my fuel tank is aluminum, and above deck under the leaning post seat. I have full access. The only vent for it is a spring loaded cap vent. I've always wondered if the thing ever actually vents due to tank pressure? Anyone else have this type of setup?

Thanks,
Dave

 

[Chris1956]

Make sure the fuel is clean and has no water in it. Use new fuel in a portable tank, if you can.

Your motor likely has the SLOW system which limits RPM to 2500 or less, when it detects overheat. I suggest you test the overheat sensors and diode in the wiring harness.

 

[SweetD]

Make sure the fuel is clean and has no water in it. Use new fuel in a portable tank, if you can.

Your motor likely has the SLOW system which limits RPM to 2500 or less, when it detects overheat. I suggest you test the overheat sensors and diode in the wiring harness.

Thanks Chris, that is the plan with the portable tank test. I did take a peek in the on-board fuel tank last night and from what I could see through the pickup and fuel fill, the interior is very clean and clear. I religiously treat my fuel with Marine Sta-Bil and Sea Foam. The tank is only 30 gallon so I run through fuel pretty quickly. I also emptied the H2O/fuel separator into a glass jar and noticed no separation at all, and I have never had that problem in the past.

I will also test the overheat sensors, my motor does have the SLOW system. Thanks for the idea, hadn't focused on that yet!

Dave

 

[SweetD]

Tested t-stats tonight in the limited amount of time I had, they are opening and closing fine...just one more thing to check off. Can't wait to get the boat in the water to try the aux fuel tank, etc. Starting to think powerpack.

 

[SweetD]

Today I wanted to check the key ignition switch on the remote controls. So I dis-assembled the remote control (took awhile), tested the key switch on the bench per the manual - it tested fine, But, I felt like the choke/kill switch was sticky. I went to re-assemble it back into the remote control unit and I snapped the key switch neck off by over-tightening the retaining nut. I was so pissed.

Ran over to my mechanic's place and he had the switch in stock, so $77 later I re-installed the switch, buttoned everything up, and recruited my buddy to go for a cruise.

I am happy to report the motor ran flawlessly. At the end of the day I'm not really sure what corrected the problem. I think it may have been a loose connection at the battery from last year. Or something to do with the sticky switch. I will say I learned a ton more about my motor. Here's to a trouble-free boating season moving forward.

Dave