Johnson 90 hp difficulty starting when warm

[wallyuwl]

I have a 1985 Johnson 90 HP V4. Parents owned it 30 years, new to me as of spring 2018. No hour meter, but probably about 200-250 hours on it. Typically we drive it 5-10 minutes, then stop for 20+ minutes before starting again. They used it the same (usually driving 5 min or less, actually, before stopping). Typically it re-starts fine. The problem I will describe below also occurred once last summer under similar circumstances regarding drive and stoppage time, but I didn't think much of it.

Yesterday we drove it 15 min or so at about 3800 RPM (ran great), then stopped for 4-5 min, then I tried to restart it. It turned over but would die right away even with raising the throttle lever. Did this 4 or 5 times. Then I think it was getting flooded a little and would not even turn over when I tried to crank it several times. So I let it sit another minute and finally got it to turn over and not die, through really raising the idle lever. When it ran it was rough and seemed bogged down. Thankfully we didn't have far to go to the landing.

The VRO is removed. The battery is 10 yrs old, but still seems OK since it starts fine when cold and has always been on a charger/tender since new.

I have read it might be the ignition coils, but it has 4 of them. To the eye they look OK, not melted or cracked or anything. All 4 are original.

I have some mechanical skill, but it is the diagnosis skills I'm bad at. Things I have replaced on the engine since owning it: rectifier/regulator (2018), thermostats (month ago), impeller (month ago), one power pack (month ago), primer bulb and fuel pump (both last week), tightened throttle arm nuts (helped solve a surging problem, last week), spark plugs and wires (month ago). About a month ago I also did the Johnson Engine Tune treatment (similar to combustion chamber cleaners for cars), was not that bad actually and hardly smoked.

I am actually taking it to the mechanic tomorrow to get the carbs rebuilt, throttle checked (adjusted and lubed if necessary), and fuel lines inside the engine replaced since they are original (from inlet to fuel filter, then from fuel fliter to fuel pump - an easy job but might as well have him do it instead of me having to buy the lines and have a bunch left over). The fuel lines from the tank to the motor are about 6 or 7 years old and appear fine.

Any ideas? Things I should mention?

 

[oldboat1]

If you decide to do a bit more before bringing it in, you might get an adjustable spark tester and test ignition strength when hot -- may need to replace the other power pack. Additionally, carbs probably need cleaning and rebuilding (something you can do yourself and save big money.) If you bring it in, just give them the symptoms. Let the shop diagnose and give you an estimate before doing the work.

 

[wallyuwl]

Took it to the mechanic, and he tested spark and compression (140 on all, pretty good for a motor that age). Thinks it is fuel related. Said the spark plugs were all wet. Thinks the carbs needles are not seating, causing it to send more gas to the engine (thus the wet plugs). So it is getting a little flooded, and when trying to restart soon after shutting it off there is still gas in there. Was going to get the carbs done anyway (not something I wanted to handle myself), so that is good. Will see if it still does it this weekend. If so I will replace the power pack and see how it does. Just ordered new power pack and coils, just in case (can return if needed).

 

[Joe Reeves]

Look closely under the flywheel at that green ring of a stator.

If a sticky looking substance is dripping out of it, dripping down on the powerhead area, that would result in a AC voltage drop to the powerpack's capacitor which in turn will result in weak, erratic, and eventually no ignition (spark).

If the above happens to be the case, replace the stator regardless of what kind of readings you may get from it!

NOTE: The excessive fuel within the engine is most likely due to your starting attempts if indeed the above condition exists.

 

[oldboat1]

10 yr. old battery? Motor has to crank at approx. 300 rpm for starting. Good idea to have the charging system checked as well.

 

[wallyuwl]

I was going to replace battery next spring, but am having it done at the mechanic since his price is good. He load tested it and it still was on the low end of good, so it is being replaced with one exactly the same.

Stator looks good, nothing dripping. If it still has trouble starting when hot I will replace the coils (they look fine, no melting or cracking and the wires look good) and other power pack.

 

[racerone]

Well -----I would do some testing trouble shooting instead of throwing parts at the problem.----A 10 year old battery tells me something.------And I would take the starter apart for inspection and an ohm test.---Perhaps new brushes for the starter.

 

[wallyuwl]

Got the boat back today and took it out. Said spark looks great and compression is 140 all around. Runs great, idles very steady. The real test... took it for a 20 min drive, stopped for about 3 min and tried starting it up. Started up with just a little raising the throttle lever. Did not need to prime it. Did not die, though it did take 10 to 15 sec to get to consistent idle. Perhaps issue was carbs. He said they were really clean but needles worn (never been rebuilt and 34 yes old).

Will try it again in a few days when I have time. If all is well then as well, I will return the power pack and coils.