1999 Johnson 90 Port side does not appear to be firing

[Kashwakamak]

Have had this boat for 9 years. 7 years ago I replaced oil pump, power pack, plugs, inductive spark plug leads, cleaned and adjusted carb floats, and added a fuel/water separator. I run fuel stabiliser in it all the time so I never have to worry about gas sitting in it over the winter untreated. Runs great, normally...

Two weeks ago I was running at half speed when I noticed the engine start to make a light "knocking" sound. I docked and checked and appear to have spark on all four plugs. Replaced plugs. Checked to see which cylinders were firing at idle tied to the dock. The port side cylinders do not seem to be firing as when I remove both of the leads the engine continues to run with no noticeable RPM drop (although there is spark). When I do this with the starboard side leads, the first one removed (top) drops the revs by 1/4, then removing the second lead causes the engine to stop running.

Put all four leads back on the spark plugs, fire it up and it seems to be idling fine. I spray gas into the starboard side carbs, top first, and the engine starts to bog. The same happens on the bottom. When I do this on the port side, nothing changes. I hold my hand over the carb intake on the port side carbs for a few seconds while the engine is running and I get plenty of fuel coming out when I release my hand.

I have changed the fuel output from the VRO pump to redirect port and starboard flow to the opposite fuel manifold rails and there is no difference in performance. When I disconnect the leads, it still appears as though only the starboard side is running.

I have done a compression test and the cylinders are all within spec with the largest difference being 12 PSI between cylinders. I checked the engine temperature after running at idle for a few minutes with a laser temperature gauge and they all seem to be running at 57 to 65 degree's Celsius.

I just replaced the power pack and am still having the same problems... (expensive mistake). There are two coils on this motor; the top coil feeds the top two cylinders, port and starboard, and the bottom coil feeds the bottom two, port and starboard. I do not think the problem would be coils, or the power pack. I am using inductive spark plug leads and noticed one of them had a split on the insulation and replaced it with one of the old ones.

A local guy said that the carbs feed the opposite side cylinders on this motor, yet when I spray gas into the carbs on the starboard side, the engine bogs. The port side does nothing and this is the side where I can unplug both leads and there is no difference in the RPM's. Whereas if I unplug both starboard leads the engine stops.

Would it make sense that I could possibly have a fuel problem on both carbs on the port side?

As well, when I do take it out to see if it is working at high speed I am able to get up on plane quite easily. This makes me think I am getting "better" spark or fuel flow at higher RPM's, but still hear the faint knocking noise and it is not even close to it's regular top speed of ~48 MPH.

I have a new water/fuel separator filter but have not replaced it yet.

I look forward to any thoughts and thank you in advance!

Cheers,

Jeff

 

[racerone]

If this is a 60 degree looper the carburetors do NOT feed the opposite side.-----Not sure why your " local guy " would say that.----Have you looked at the water pump / replaced the impeller in the last 9 years, yes or no ?

 

[Kashwakamak]

4 Cylinder 60 degree outboard.

I thought that comment was weird too. No, I have not replaced the impeller since I bought it used in 2010. Having said that, the stream is good and the temperature is not hot enough that you can't put your hand into it.

 

[racerone]

Well , you need to install a new impeller now just because it is time.----Perhaps look at the optical sensor for ignition.-----Swap top coil to the bottom and test run.----In a modern precision engine the difference in 12 PSI would be a concern to me.------Have you ever checked VRO oil output with a test procedure ?

 

[Kashwakamak]

What should I be looking at for the optical sensor? I purchased a manual (which turned out to be photocopied) and it is missing pages 3-24,25,26,27,28,29 of the ignition. I'll look into the impeller as well.

I have a spare coil from when I replaced one years ago troubleshooting the problem which turned out to be the power pack. I'll try putting that one in to see if there is a difference.

I have not recently checked the VRO output, but appears to be working well. I did check it to make sure it was working when I was initially troubleshooting and that's when I decided to replace it. I have read since that the model of the VRO pump on this engine is not as fickle as the earlier type.

 

[racerone]

Blunt statement here.-----If you have money to spend to buy parts as a guess you will not have problems keeping this motor running.------I would be doing the VRO output test once a year.-----Have you replaced the filter in the VRO tank ?-----Tested the VRO ---" no oil alarm " ever ?

 

[Kashwakamak]

I'm being cautious now I bought a new power pack for no reason... I checked the oil pickup filter last year and it appeared to be good. I also monitor the oil level (I put a piece of tape on it with markings and check the markings regularly). Last fall I let it get low and the warning alarm did fire.

 

[racerone]

But there is a low oil in the tank alarm AND a " no oil is being pumped alarm "----Have you tested the latter ?

 

[Kashwakamak]

No I have not tested that one.

 

[Kashwakamak]

You had mentioned testing the optical sensor:

Perhaps look at the optical sensor for ignition.----- What would I be looking for?​

Can I try reversing the coils (turning them around so port is starboard, and then plug in the opposite leads) temporarily to see if I move the problem to the port cylinder bank? I am thinking that would eliminate the coils...

 

[racerone]

Sorry----Testing is up to you.----I get slammed by some folks who want the instant answer.

 

[Kashwakamak]

I think the problem is solved. Last weekend we checked the timing with a timing light and verified all cylinders were firing at both idle and high speeds.

Took the carbs and manifold off and verified the reed valves are good. Took the carbs apart and checked all seats, needle's, and gaskets. All good, but... upon reassembly, the top carb was leaking gas out of the top of the bowl into the motor. It turns out the gasket had shrunk enough that it was no longer making a good seal between the carb and the float bowl. Went to the marina to get a new seal and bought the repair kits to eliminate any problems. As well, a new float bowl as the old ones were warped and were no longer contacting the top of the carb properly.

I'll work on it again this weekend and post whether or not I have any success.

 

[Kashwakamak]

Well, we also replaced the bowls on the starboard side and were still having problems. Took into the local mechanic who moved the timing back to factory (it was advanced by one tiny notch) and now the boat runs fine and idles properly again.

But now... there was a ticking when in forward gear. Turns out the pinion and forward gears have a broken tooth each. Now I get to rebuild the lower unit.

Thanks again for your ideas Racerone

 

[racerone]

I see many problems with the " batwing " gearcases.-----Sudden failures due to teeth breaking on pinion and forward gear.-----Make sure you get shimming correct if repairing this yourself.