Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

[X53Gunner]

I have a Johnson 70hp, I can put it on the muffs and she will start and idle all day long like a champ. As soon as I go and put it in the water I doesn't want to start very well (takes like 20 min) and when I drop her down into idle it will want to fall off and die. Also the last time I took it out It acted like it was dropping a cylinder. Would run at very low speeds and after awhile (5 min of running) would kick back in and run up to speed again. However still always has the not wanting to start and idle issue. I just checked compression and I have starting from top cycleneder to bottom..130/130/120 I'm thinking this should be fine. Wonder if I should start looking at carbs? Also i have rebuild the fuel pump already..Just don't understand the whole on the muffs and not in the water thing.
Thanks for your time
Scott

 

[racerone]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

These motors will run just fine on muffs, there is no work for the motor to do !---------So it will sound just fine to the untrained ear, even running on 2 cylinders.--------Clean the carburetors, inspect diaphragm in the fuel pump, check for STRONG spark on all 3 cylinders.

 

[oldboat1]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

20 minutes trying to start the motor is a long time. What's the procedure? You do have a significant compression drop in one of the cylinders, and it could be a factor. I think, though, that cleaning/rebuilding the carbs may be the place to start, as well as checking to be sure that there isn't some exhaust blockage somewhere -- could have a nest up there in the leg. The backpressure is too much for it (as opposed to running it on muffs), and that can be a result of a number of things, unfortunately. But dirty carbs is one of the things, and could also account for the erratic operation when you do get it fired up in the water. You need a test tank (a barrel or similar) to work on it. Got any temperature issues? A blockage could be responsible for that too.

 

[racerone]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

With that amount of cranking it is possible that the starter has been damaged.---That leads to slow cranking and harder to start condition.-----Definitely check things out including the starter motor.

 

[Bob_VT]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

I think you need to check the spark and maybe the powerpack. As mentioned above.......it will run and idle ALL day on less then all cylinders.

I would start with the spark.

Have you ever shut it down and then removed the plugs? Are they all the same temperature? Are any of them looking wet from fuel?

First the spark.
Then the carbs.

Yes don't burn up the starter.

 

[Joe Reeves]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

(Engine Won't Start or Hard Starting In Water)
(Joe Reeves)

The Evinrude and Johnson engines, starting in 1973, have what is called Magneto Capacitance Discharge ignition, self contained, not dependent on battery voltage. The engine must turn over at least 300 rpms in order for the flywheel magnets rotating past the stator ignition generating coils to supply approximately 300v AC to the powerpack(s), which in turn is needed to supply power to the coils etc etc (spark).

In the water, exhaust back pressure is encountered due to the fact that the exhaust housing (housing between the powerhead and the lower unit) is filled with water. This would drag down the needed rpms, affecting ignition.

Normally the clue to this type problem is that the engine starts fine on a flushette (hose), but is very difficult to start when in the water.

Should this be the case, check the battery, clean and tighten all conections (use a wrench or pliers, not your fingers). Any cable that gets overly warm or hot indicates either a loose, or tight but dirty, or internally corroded cable. And of course check the starter itself.

 

[X53Gunner]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

I have a new starter on the motor, also I have rebuilt the fuel pump so it has a new diaphragm in it. Maybe I'll have to rebuild the carbs and also get a spark tester to see if the spark is enough. I'm wondering do motors around this year have the cut off when they overheat and could that have been why I thought I lost a cylinder while running(lost like over half the power)? Maybe its running lean and overheated and it went into the mode were it cuts power but runs enough to get you back to shore? Then while running back to shore on the two cylenders (or reduced power) maybe it cooled off enough to give me full power back. Hope this makes sense. Thanks for all the input by the way!!!
Scott

 

[oldboat1]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

running with the correct oil to gas ratio, right?

 

[X53Gunner]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

Yep 50:1

 

[racerone]

Re: Mid 80s Johnson 70hp 3 cylinder 2 stroke runs on muffs not in water?

No heat sensitive electronic cutoff on those mid 80's motors.---Check to see if you have strong spark on each cylinder.--If spark does not consistently jump a gap of 7/16" you have ignition problems.