Re: 1970's Evinrude 65hp question
IMO, the three cylinder loopers are among the best engines that OMC ever made. I have a '72 Johnson 65hp, which is essentially the same engine as yours, except it has hydro-electric shift, instead of hydro-mechanical shift.
I would do a compression test on it first. If you are lucky, you will see values in the mid 140s, but may be more likely to see them in the 120s to 130s. Unless the values are quite a bit below that, are more than 10% apart from one another in value, or you have some other, obvious and serious mechanical issue, you should have a pretty decent powerhead.
I would replace the gear oil and drain it into a clean cup, so that you can check for the presence of water, metal grit and/or other debris. If the oil is clean and clear of water, you should be OK in terms of seals and mechanical condition. You gearbox uses an internal pump and a set of poppet valves to create and direct hydraulic pressure on a piston, which moves the clutch dog. Since the gear oil acts as the hydraulic fluid, its important to use the right oil. The original name for the correct oil was "Type C" and the currently recommended oil is BRP "Premium Blend." I don't have a lubrication chart for your motor, but in the hydro-electric version of the gearbox, 25.3 ounces of gear oil are required. I suspect that yours requires the same or very close to that amount. Don't forget to use new crush washers under the heads of the vent and drain screws every time you remove them!
Also change your gear oil frequently, since that is the best way to keep your gear box's "innards" clean. Hydro-electric and hydro-mechanical gear boxes don't like dirty oil, because they depend on the ability of the piston to move freely. The presence of water and/or grit tends to cause problems, and eventually, shifting problems. As for what the term "frequently" means, that is relative to how much you use the engine. I run my motor quite a bit, 12 months per year, so I do it about 3 times a year.
Depending on how long the motor has been sitting, you may or may not need to do a carb rebuild. If you do, you will need a special screwdriver to remove the fixed, high speed orifices in the carbs. If memory serves me correctly, there is a thread somewhere in the iboats server on this subject - I would do a search for something along the lines of "evinrude johnson 65hp carb rebuild." A link & sync after the rebuild would be a good idea, too.
The ignition system on your motor is pretty simple. It has an alternator, which is made up of the flywheel and the stator, a timer base, a power pack and three ignition coils. Once you get an OEM manual for this motor (available online from a variety of sources), you can get into the theory of operation. Suffice it to say, however, that you may experience ignition problems at some point and have to do some trouble shooting and parts replacement. Most of the testing that you need to do to isolate a failed part, can be done with a simple multimeter. If you ever end up having to replace ignition parts, I recommend either Sierra or CDI parts, because they are about half the price of the BRP parts. Further, the parts that BRP is now selling as OEM items for your motor, are reputed to be aftermarket parts anyway.
Another common replacement item on these motors, is the rectifier. Its function is to convert the 300VAC that the alternator produces, to 12VDC for the motor's charge system. In order for the motor to recharge your battery and provide a signal for a standard tach, this must be working. Your alternator only puts out 6 amps, so don't expect to run a lot of gear off of it, without some battery drain. Your system also requires a battery of at least 70 amp hour capacity.
If the motor has the originally specified Champion UL77V surface gap spark plugs, get rid of them. Replace the plugs with Champion L77JC4 plugs. I think you find that the motor will run better, throughout the operational range, with these plugs. Whatever you do, don't run NGK plugs in it - I can't explain from a technical perspective why they don't work well, but my local BRP dealership swears that they don't. I couldn't believe that there could be that much difference in a plug that was billed as an "equivalent plug," but he was right - the motor ran like crap.
As has been already mentioned, doing a water pump rebuild is always a good idea with a motor that is new to you. That may require little more than an impeller change, but it may also call for installation of a complete kit. You'll just have to take it apart to see what the cup and housing look like. Once you get it all back together, run the motor on a hose/muffs. Provide enough water pressure to feed the engine, but not so much that you are force feeding the cooling system. You should see a bit of mist coming out of the pressure relief holes on the back of the midsection and the t-state should open up in about 60 seconds, give or take a little. Once it does, you should see water begin to flow out of the vertical slits, located above the cavitation plate.
Your motor does not have a telltale (pee tube) in it. If you want to install one, you may find this thread to be interesting. I left the brass nipple in mine, after talking to a bunch of people about the galvanic corrosion issue. While I don't mean to discount the advice of folks here and the corrosion factor in general, I just don't feel that its going to be a big enough problem to warrant a lot of worry. As I said in another thread recently, I think the arteries in my heart will "corrode" and kill me, long before this nipple falls out.
http://forums.iboats.com/showthread.php?t=287975&highlight=johnson+65hp+tel+tale
One other peculiarity of your motor, is that it has an automatic, thermal choke function. This works through a temperature sensor, located on the port side of the cylinder head, and a two stage choke solenoid. When you turn the ignition key on, if the head is below the predetermined temperature, the thermal sensor sends an electrical signal to the choke solenoid, which actuates the solenoid/choke butterfly halfway. While this seemed like a good idea in theory, OMC found that it was causing motors to run too rich often times, which caused fouling problems.
See the following Service Bulletin, for instruction on how to bypass this system. Pay particular attention to the jumper that must be used to get full actuation, when you use the choke switch at the remote control.
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