newbie - please help '75 85hp Johnson

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bharle

Cadet
Joined
Aug 29, 2006
Messages
11
I'm new to boat motors and need help to get the old pontoon back on the water! The motor above starts good, purrs great, humms wide open, then after awhile it is like a couple cylinders cut out, like a switch turns them off. Seems electrical.

I was advised by one person the water pump was recently redone before I bought it and the small spitting of water out the back is normal that it never does have a solid stream. Another told me the pump wasn't working well and the engine maybe getting hot and the temperature sensor is reacting and cutting out the cylinders.

The motor doesn't seem excessively hot at anytime.
There is only a slight spitting of water out the 2 holes in the back above the water line.
I dropped the lower unit and took apart the water pump. Seems tight to me but there is a groove on the plate. I ordered an impeller rebuild kit from iboat.

1. What is the correct orientation of the impeller? I'm not sure what direction the 'cogs' were when it popped out.

2. Any hints on the installing the rebuild kit I should be wary about?

3. Any other ideas about this problem?

4. The starter isn't perfect, can I buy the starter drive someplace without the complete starter? If I need a complete starter, is this the cheapest place?

5. I also would like to find a tilt/trim for this motor. Other than ebay any suggestions.

Thank you very much in advance for helping me with this. Any help would be appreciated.

Bruce
 
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ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: newbie - please help '75 85hp Johnson

The impeller fins will be properly alligned if you pin the impeller to the driveshaft and then push the housing down on it while turning the driveshaft clockwise. It helps to oil the impeller and housing, or use dishwasher liquid if you wish.

The small shops that rebuild automobile starters around metropolitan areas are equally capable of doing a first rate job on your starter.

The water coming from the two holes should be a spray most of the time if you have the mid section full of water. When you run the boat, It should increase in amount and velocity.

The temperature switch is only there to sound the horn in your control and does not have the ability to do anything else. Since it is only on the starboard bank of cylinders, it does not tell you if the port bank is overheating.

If the engine overheats, it will usually be on one of the banks and not both, and it would stop the pistons.

It is much more likely that you are losing one or two ignition coils when they warm up. The coils are green and are arrayed across the top of the engine on a rack. Look them over carefully for cracks, discoloration, or melting. If you find those conditions, you should consider replacing them. Unbolt them from the rack and clean the grounding surfaces well, then clean all of the wiring connection.​
 
bigbob_FTW

bigbob_FTW

Petty Officer 1st Class
Joined
May 10, 2007
Messages
290
Re: newbie - please help '75 85hp Johnson

I have the same motor. Check to make sure you don't have any cracks in the coil covers. I had a couple and caused the same problems. I fixed them by applying some pig putty to the cracks.
 
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bharle

Cadet
Joined
Aug 29, 2006
Messages
11
Re: newbie - please help '75 85hp Johnson

Thank you very much for the help guys, you have no idea how much you just helped me! It is much appreciated.

A couple of the coils do have small lines on them which I'm now assuming are cracks. When you say putty, do you mean a silicon caulk type of stuff or plumber's putty kinda stuff?

The video of the water pump rebuild was perfect for me. Again thanks.

Are there any issues to keep in mind when putting the lower unit back on the motor? My brother in-law was suggesting I put silicon or other sealant around the small 3" long pipe that extends up from the water pump which stayed on the water pump when I removed the lower unit (good/bad? I have no idea). I was told by the previous owner when he 'rebuilt the pump' that the water never really sprayed out of the two rear holes but water came out from everywhere when hooked to a garden hose. He said he was scared but was told it was normal. I'm wondering if there wasn't a good seal between the lower unit the upper part?
 
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ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: newbie - please help '75 85hp Johnson

Silicone around an outboard is a poor choice. Find something that does not dissolve in oil, gasoline or alcohol.
 
jtexas

jtexas

Fleet Admiral
Joined
Oct 13, 2003
Messages
8,646
Re: newbie - please help '75 85hp Johnson

On the starboard cylinder head, find the temp switch, its got a tan wire coming off it...a few inches down the wire is a rubber sleeve covering a disconnect. Disconnect the tan wire and hold it (not the switch end) against the engine block with the keyswitch "on" - you should hear the overtemp warning buzzer from the control box. If the horn doesn't sound, open the control box to troubleshoot the buzzer and wiring.

Manual calls for "OMC adhesive type M" or something on the joint between lower unit & mid-section; I use permatex #2, works fine. But water will come out all over with the hose running.

aftermarket power tilt will cost more than the motor's worth - next best choice is to salvage one from a blown motor.

good luck.
 
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ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: newbie - please help '75 85hp Johnson

Patching the ignition coils is not going to fix them if they are bad. Bad coils can ruin a perfectly good power pack.
 
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