Need help – 1977 Johnson 85 hp V4 motor runs rough erratically

[Patrick Mitten]

Hello fellow members:  Thank you for your consideration and advice.  My Dad purchased a new Johnson 85 hp V4 outboard motor back in 1977, and the engine has been meticulously maintained.  For the past 3 years, the motor runs erratically at times, and when it acts up the motor seems to loose power from two cylinders, causing the motor to bog down.  Last summer I had our mechanic replaced all of the ignition parts, hoping that would fix the problem.  The gas tank was also removed and cleaned, and the fuel line was replaced.  The erratic engine problem still exists.  I believe that each of the two carburetors serve two cylinders.  My mechanic is checking the carbs now to see if something inside is causing an intermittent fuel flow issue.

Is there anything else that I can check?

Thank you, and happy boating!

[joecb]

Question, what kind of ignitions system toes your motor have ? 12 Volt and distributor? magneto? belt driven? or a more modern system?

Joe

[crosbyman]

wait for the carb   job results          sounds like fuel flow issue …doesn’t take much to clog a jet  or inlet needles

have you ever tried a can of  fuel system cleaner  with some fresh fuel …..

if carbs  were… fine….  check  for proper venting …

the other possibility  is a heat related  problem affecting a component… try  running with the cowl off

Joining AOMCI has priviledges 🙂

[fleetwin]

Well, I’m sorry you replaced all those ignition parts, sure hope you kept the old ones.  The issue you are having could be caused by most anything.  It is bee.  st to let a good technician ride in the boat to see it misbehave so he can diagnose it more effectively.

These engines were some of the best produced by OMC for sure.  The ignition system is fairly simple and easy to diagnose.  The one thing that was not replaced was the “stop circuit”.  This engine is stopped by grounding the capacitor inside the powerpack so it can not store a charge.  So, if there is a bit of a problem in the stop circuit, you can have a range of running issues ranging from no spark at all, to an intermittent miss.  The way to rule out the stop circuit is to simply disconnect the black/yellow lead from the powerpack and retest.  Keep in mind, you will not be able to shut the engine off with the key switch, which could be dangerous, but you can choke it to shut it off.  Also keep in mind that just because all the ignition parts were replaced, does not mean a possible bad ground was not taken care of in the process.

Some dirt in the carburetors could be plugging one or more of the high speed jets intermittently causing a problem like you describe.  Once again, this is best diagnosed by having a technician along while the engine is misbehaving, so he can manually inject each carburetor throat to see if that helps or makes a difference.

So, the shop is cleaning/inspecting the carbs now, hopefully that will solve the issue.  But, if it doesn’t try to make a video of the engine misbehaving and post it for us, this might help us help you…

[Author]

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