Johnson 5.5 won’t idle

[Buster]

I’m restoring a 1954 Johnson 5.5 outboard.  Initially, it ran well in a barrel and idled right down where you could almost count the flywheel rotations.  After a couple of trips on the water, the engine does not want to idle down.  Runs well at speed but idling down the engine will quit.  Have been using the required 16:1 oil mix ratio.  Any clues to restore the idle?

[crosbyman]

could be  clogging due to poor crankcase drainage of excess fuel oil mix.    I would try  25/1  oil mix with quality oil        open up  or close  idle mix knob a bit   tocheck for reaction .

presumably carb has been  gone over   side channel  flushed out   top idle  chamber cleaned out

measure coil resistance on secondaries  (boot to grd  should see solid  4-8kohms )

btw  pump or pressure tank used ???

 

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• This reply was modified 2 years, 7 months ago by crosbyman.

[crosbyman]

see description…

 

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joesnuffy

[Mumbles]

It’s quite possible the motor may have sucked some water or dirt (rust) out of the tank and it is plugging up the low speed circuit in the carb. Can you see anything in the sediment bowl? Is the tank building and maintaining air pressure at idle speed?

Have you tried adjusting the mixture needles on the front of the motor?   It might need some ignition work to as the points may be dirty or pitted due to old condensors or oil getting on them. It’s also highly recommended to stay with the required 16:1 mix as using anything else increases the chances of the motor burning its bearings out or throwing a rod. Just saying….

[reivertom]

Go through the carb again. I always try the most obvious and easiest things first. It sounds like some dirt got dislodged and is blocking a passage on the low speed side.

• This reply was modified 2 years, 7 months ago by reivertom.

[fleetwin]

You mention that the engine runs OK at full throttle but won’t idle.  It is possible that one cylinder is dropping out when the RPM is lowered, so you may want to use one of those neon inline spark testers to be sure you are not losing spark at lower RPM.  Perhaps you just have one bum plug.  Just cuz the plugs are new, doesn’t mean they are good.  Always start with the simplest issues.  Like others have said, have a look at the sediment bowl to ensure the carb hasn’t sucked up water/rust/crud.  Are the packing nuts snugged up to ensure the needles don’t move around on their own.  You might try resetting the initial needle settings and readjusting.   Does the engine sneeze/cough when the throttle is lowered?  If so, perhaps the tank isn’t  holding pressure.  Keep in mind that the tank must hold pressure or else there will be a crankcase leak and the engine won’t idle.

Finally, I would be very careful about using a 24:1 mixture to evaluate the drain system.  This is a good way to damage the rod bearings.  Always start with the simple things, including rechecking compression.

[crosbyman]

did you ever  replace the plug wires…..sometimes they go open in the bend  depending on the position of the throttle plate ..

 

this could explain  dying a low idle  has suggested by  fleetwin ‘s tip  of one cyl dropping out

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[crosbyman]

endless discussions on fuel oil… opinions differ   seems 16/1 was for  SAE30 grade oil     with modern tcw3 …24/1 seems fine     synthetics probably even better  and.. .to clean the innards  xd-100 $$$$

Johnson CD-10 Fuel/Oil Ratios | Boating Forum – iboats Boating Forums

 

I sold  5.5  Evinrude  (1955) to a friend  a few years ago and told him   use no less than  1 liter oil /25 l of fuel.

He still likes the kicker  and  says it does  load up the plugs  after a long day of fishing …he has reduced   the oil ratio (less oil) a bit  and the engine runs fine……till it dies I guess 🙂

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• This reply was modified 2 years, 7 months ago by crosbyman.

[fleetwin]

My opinion stems from seeing too many of these engines with vent holes in the block where the connecting rod exited.  These engines barely smoke at all at 16:1 when in good condition and in proper tune.  So, like you say, let the owners decide.

[aquasonic]

Had a 1959 Evinrude Lightwin that ran well at first, then wouldn’t idle like your motor. The problem was that the points set screw rotated just a bit on one set of points, and the timing was thrown off. Just needed to reset the gap, and used a little more torque on the set screw.

It may pay to revisit the ignition assembly. Once that is checked, the link and synch adjustment is important to achieve the proper relationship between fuel supply and timing.

[Author]

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