1972 Merc 75, just got one for free and need a little advice

[dnylrq]

So as the title says, I've gotten a 1972 Merc 75. I was told it may need a carb cleanup because it wasn't running well and/or had been sitting for a long time. I opened the top and found all the wiring insulation was destroyed, and some small stuff has crumbled when I tried to move it... I've managed to get the ignition apart and sourced wiring that I can use to redo that much. It's become abundantly clear that getting parts is a PITA. Perhaps there is a cross-reference for updated parts?

So to be upfront, I've never worked on an outboard motor, nor have I done much work on anything with a carb, and have never dealt with a points style ignition. I've obtained the service manual to help me through some of it, and thankfully I am mechanically inclined. I'm sure that the wiring is going to be the beginning of all the fun for me, so I was hoping to get some advice on points and maybe on the other things I should be checking on, and also maybe the best order to go about it.

Also, all the info I have I believe is correct based on the serial number, but I make no promises =D
SN: 3277808 (Which no website can find...)
Black with Blue Stripe
7.5 HP
Thunderbolt II w/ Phase Maker & points
Long Shaft
Type "B" Carburetor (round bowl, single float w/ integral fuel pump)

 

[GA_Boater]

Welcome aboard.

I found your serial number. It's in range for the 1972 7.5 HP motors. I guess you tried to Google.



Now you need a manual. This is better than no manual at all - http://www.iboats.com/Mercury-Outboa...view_id.373450

 

[tpenfield]

Old outboard parts are generally hard to find and expensive. I have the 1969 version of the same motor. The wiring on mine was all crumbling and shorting out. I made a new wiring harness for short $$$. The drive shaft of those motors is regular carbon steel, so they tend to get pits in them and start leaking oil at the water pump seal.

A few years after your model, Merc switched to stainless steel drive shafts. I picked up a 1980 drive shaft for $160 on eBay. . . :facepalm: again big $$$ for the parts.

Overall, it is a good engine, I like my Merc 7.5 a whole lot better than my Johnson 4. So if you can get through the aging issues, you may have yourself a nice motor.

 

[merc850]

I would suggest getting a manual for it because you need to know about the special procedures, timing etc. required to maintain it.

 

[flyingscott]

You have to get a mercury service manual for that because of the phasemaker ignition. The stator is available from CDI Electronics new. The coils and points are available new from mercury. The main thing is NEVER use the kill switch unless it is in the water that can destroy the stator. Forget everything you think you know about ignition systems because anything you do know won't apply to the phasemaker. I have heard that the ignition can be converted to regular points from a different model somebody here might know.

 

[dnylrq]

As far as the manual goes, I had already grabbed the clymer manual before posting. Sounds like the other one posted may have been a better bet, but too late now lol. I will definitely heed the advice given so far. I've gone into this whole project with a clean mind. I don't assume that I know anything about it and I am taking my time with it. The phasemaker doesn't really scare me all that much, I just know that I need to learn more about it before messing around with it too much.

I am curious about the kill switch though. I'd never run the motor without at least a test tank, but it seems odd that pressing it would murder the stator. In any case, I will take your word for it =D

So after I'm done fixing the things in the ignition system, where should I head to next? The motor and housing were fairly clean, so as of right now I don't believe there is any type of oil leaks. I know I need to change the gear oil in the lower unit, I would imagine draining it and then disassembling it would be the next step? Perhaps checking the parts of the water pump?

 

[CharlieB]

Changing the water pump impeller is ALWAYS a good idea and cheap enough insurance to ensure a cool running engine.

I would almost bet money your impeller is very old, dried out and the blades set into curves so hard the amount of water pumped is far less than optimal.

 

[60sboater]

I have a '73 9.8 and it's the last yr of the PM ignition. I had to replace all the wire...only the capacitor,one charge coil and points were good...points looked new. As mentioned,CDI in Alabama is a good source for ignition stuff. Mine runs but I'm using a larger '72 25hp Johnson on my boat at present.

Check your ignition coils with an ohm meter.

 

[flyingscott]

A standard ignition system does not use ground as part of the ignition system. In those systems when you kill the motor the switch sends power to ground bypassing the ignition. On a phasemaker ground is part of the ignition circuit so when you hit the kill switch it stops power from going to ground causing a backlash into the stator. When the motor is in the water the backpressure slows the motor down fast enough to not cause damage. On muffs it can spin for two long and cause damage. Be very careful with the coils do not take the nuts off if they are original you could break the studs at $120 a pop they are pricey

The seloc manual if your library has it will have the specs for testing the stator you can copy them.

 

[dnylrq]

So here's pics of what I have so far. The order is reversed on photobucket, not really sure how to change it, but I'm sure it will be ok. Not really sure how it all should look, so I would appreciate any feedback. Also, I'd like to say thank you to all of you who are replying and helping me along!

http://s7.photobucket.com/user/dnylrq/slideshow/Merc 75

 

[60sboater]

You can check the red module and coils with an ohm meter. The cap can be tested with an analog ohm meter to see if it charges and discharges but will not give the actual value of capacitance.

 

[flyingscott]

Looks like most of the wiring is good it will be a fun project. They have pretty robust points so should be able to clean them up

 

[dnylrq]

Flyingscott, I now see those pics don't show the utter destruction of the wiring. I'll have to get a good pic of that stuff later today. I don't think I've seen wiring this bad since I pulled the old rotten knob and tube out of my house LOL. As far as cleaning the points, I assume a file will work?

 

[flyingscott]

Nope those are in good shape if you have anything to attach to it's in good shape. I have had those where the is nothing left of the wires. That is an extremely common problem with mercury motors of that era and it gets much worse.

 

[dnylrq]

Here's what the wires really look like. Can't imagine using these to any extent

 

[60sboater]

My 9.8 wiring was worse. I got new wire from CDI and it is only 18 gauge...they say it can handle the high voltages in a PM ignition. Be careful how you route the wiring so no binding or stretching takes place.

 

[dnylrq]

Will do. Thank you for the advice so far everyone!