Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Hello Crew,

    Hope you are all enjoying your summer and anticipating a drift filled winter.

    I have a 1987 4hp Johnson model J4BRHCUD two stroke (original owner) with fairly low hours over the years.  It still has the original plugs, runs fine and usually starts on the first pull when I remember to choke it.

   Yesterday after a fairly long run full speed for about 3/4 of an hour the engine head felt very hot.   What happened was it ran to a stop after a few seconds from top speed.  I reached around to the head and it was hot.  I waited about a minute and after 6-7  pulls it started.  I went slow for a few minutes then up to 3/4 and got back running at 3/4 after about 5 minutes.  It ran fine for that time.
 
    Does the head being anything but cool to the touch indicate a problem with this motor or impeller?   It had the right mix of gas 50:1 and right oil...I think TWC3 outboard oil.    When I run for a long time with my 1991 2hp the head is always cool. 

You might want to look at the thermostat (if it has one).  Depending on what temperature it's rated for, it might get hotter than what you're used to.  All of my outboard engines are fairly warm to the touch when operated at any speed.  In the spring, with cold water, it takes longer for the thermostats to open and will close sooner if there isn't enough heat generated to keep the thermostats open.  If you have a failed impeller, you'll know it.  More often than not when a vane breaks off the impeller, it will block the intake hole, which will starve the engine of cooling water and possibly lead to seizure.  Changing an impeller is an easy enough job to do.  However, re-assembling the gear shift mechanism is where you can have trouble if you don't make note of where it's set ahead of time.  Depending on the make and model, the gear shift mechanism may have a long adjustment nut that's used to set the linkage at the correct length for smooth shifting.  Before you take the bottom end off, use a Sharpy to mark where the threads at each end of the adjustment nut.  When re-assembling, refer to the marks to set the adjustment nut then lock it down. 

borat!  have you ever run the motor thru shallow water with a lot of mud.if you run the lower unit thru the shallows alot it can chew up the water pump.the impeller is splined to the shaft with a bronze bushing and if the mud is left in the pump it will dry.once started the vanes can't turn and the bushing shears away from the vanes.my experience with the pumps is they usually loose there prime at idle and above that pump enough to cool the engine for a while till the pump goes completely.even though it's a water cooled engine there is heat and it does get hot to the touch.years ago we use to fish the rivers in the winter as long as we had open water.my first experience with a pump starting to go bad was when we were backtrolling with an 18 hp 2 cycle evinrude. we were going slow in reverse just barely moving the boat and the water would randomly splash up a little higher  on the lower unit and you could here the water turning to steam from the heat.just reving the engine above idle would be enough for the pump impeller to start circulating water again.fyi  that small a motor it's a good idea to completely run it out of fuel for storage because there is a 2" long plastic idle pick up tube that gets gummed up if not run dry.once this happens it will not run on the idle circuit . since 1989 my boat gets used once a week in canada and since my 6 hp idle circuit got plugged now every year i run both the 6hp and 40 hp completely out of gas before coming home. that happened in the early 90's and i've not had any problems since. 

"borat!  have you ever run the motor thru shallow water with a lot of mud."

I've run my engines in loonsh!t which is similar to mud but much thinner.   I prefer to avoid it and use oars.   However, if I do run the engine in anything that might block the cooling system, I flush the engine througly, usually on the lake or river.