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bigjohnson

Regular Contributor
Recently found a 1980 mercury 7.5hp comet lightning. It needs a lot of TLC but it looks like a good motor worth fixing up.
Anyone know where I can find a mercury service manual for this.
Prefer MERCURY.
 
First thing to do is check condition of wiring.----Then check for spark.-----Check compression.----Check lower unit oil.-----Check water pump impeller.-----Maybe have a look at pistons / rings by removing the bypass cover ( 3 screws ) and a gasket you can make.
 
Where are you located? With shipping costs so high, that's a major factor.

Jeff

PS: Thanks for trying to save an old Merc.
 
The lower units are often bad from water infiltration. Driveshafts rust right at and under the water pump, causing seal to leak. These are lovely motors but Mercury made a mistake by not using stainless steel driveshafts. I have at least 20 Mercs here with the aforementioned situation.
 
But a 1980 7.5 HP mercury would have left the factory with a stainless driveshaft.-----But an older one could be fitted now.-----A complete evaluation should be done before spending coins !
 
Thanks for the response.
This motor looks rock solid and I love the overall design. The wiring
Is trashed and I've been trying to clean it up. Plastic parts are broken
But I've been fabbing my own out of aluminum and steel these parts
Will not break again.
Dropped the lower unit and it looks like new like it's never
Been removed. Drive shaft looks new.....i think it's ss.
I'll report back later.
I still need a SERVICE manual.
Free I mean I paid nothing for it.
 
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Timguy

Could you do me a favor when you get time. I'm trying to find out
Where the two TOP wires go from the CDI to ???
If you have a 1980 it should be the same as mine. My wiring is
Messed up that's why I'm asking.
Again, it's the two wires closest to the top on the switch assembly or cdi
I think one of them connect to a kill switch....maybe both do.
Thanks
 
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Here are photos. Top shows SW. box, middle is ID, bottom is timing base......not sure why the photos were rotated, that's not how I entered them....sorry.
 

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Thanks
On my motor the bottom wire was attached so I think it's good where it's at.
The top and middle wires were just hanging loose on my motor.
So are you saying that the top two wires go to a on/off switch?
 
The brown wire and the white wire go to trigger coils under the flywheel.----And one wire from stop switch goes to ground.----The other wire goes to the same terminal as the orange wire I believe.----Looks to me the previous owner could not get spark and did not want to spend an arm & leg for parts.
 
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img098.jpg
 
Thanks fazt
This diagram is clear. The previous owner(s) had the wiring
All jacked up.
I really want to save this motor since its in such great shape.
 
What does " great shape " mean here.------Nice paint and decals or a good motor internally ?------Take the bypass cover off ( 3 screws ) and look at pistons and rings.-----Install a new impeller after you get it running !!
 
Corrected the wiring and now I'm getting a big fat spark at each plug
The only wire in the correct position was the orange one. People need to buy
The service manuals. Also someone smeared GREASE all over the the manual
Pull rope starter COIL SPRING...what a mess. I cleaned that up.
Great motor?
I just like the simplicity of this specific motor. Fuel pump incorporated
Into the carburetor and pull rope assembly etc.
One thing I don't like so much is how difficult it is to reattach the
Lower unit....what a bear but finally got it with a new impeller.
Soon I will check the compression and maybe look at the pistons.
So far I've spent a whole $8 for a aftermarket impeller.
 
So, I finally got time to squeeze some fuel into the carb and with two
Pulls of the rope it started right up. Ran good for 5/6 seconds but
I shut it down because it did not pump water ( I installed a new
Impeller). Before I drop the lower unit again is there anything I
Can check for like blocked passages? Everything is open and
Clear from the thermostat to the tell tale.
 
The water level has to be a couple inches (at least), above the top of the water pump. These are not self priming pumps.
 
Yea I had the water level high up to be certain it was completely
Submerged.
I guess I will drop the lu again and blow air thru it to see if
Anything comes out.
The old impeller fell apart when I removed it so a piece may
have gotten stuck.
 
Actually, I just tried it again with more water and it did not pump.
So I removed the water hose at the tell tale and blew thru it and
air came out at the exhaust ( next to the flush screw) but no air
bubbles in the bucket of water. I cover the exhaust holes with my
fingers and blew again and bubbles came out of the bucket of
water. Does this indicate a blockage or maybe I should just
Go ahead and drop the lu so I can check my previous work?
 
Doesn't look like a blockage but it could still be a misguided water supply tube, or perhaps an impeller drive key out of place.
 
Removed the lu and put it in a bucket of water with a
drill attached and it was pumping water about half inch
above the tube. Did not seem strong but at least it was pumping.
Then I blew air thru the water hose ( at the tell tale) and noticed
there was NO air coming out of the long copper tube. Seems to me
That's where the air SHOULD come out.
Could I pull the long copper tube out to check for blockage?
If I have to I will pull the block and check.
Matter of fact if I do that I may just crack the engine open just
To check the guts.....why not?
 
I'm back
Cracked the engine open to fix a STUCK piston ring, fixed that and cleaned everything
that was dirty. Water ports were completely clear from what I
could see.
With the LU out and sitting in a bucket of water I removed the
long copper water tube and stuck it in the impeller tube
attached a 850rpm drill and turned it on just to watch water
pump out the top of the tube. So everything good there.
Reassembled everything. Motor started right up but NO WATER.
Next thing I'm going to try is removing the copper tubing again
And try to straighten it. The parts diagram shows it more straight
than this one is. In the past I guess someone could have bent
it. Which would mean it's not penetrating the water pump
housing enough.
I'm running out of ideas but it has to be fixable.
 
Sorry I missed your post of the 22nd. No 1/2" is not good force. Are your impeller fingers in the proper direction? (Turning clockwise looking from top of motor?) How is the impeller housing? Is it sealing at the top and bottom of the impeller hub area?
 
Impeller is rotating clockwise.
Maybe I should disassemble the water pump assembly and
See if any parts are missing. I see on the parts diagram
there is suppose to be a large o ring. Maybe that's failed.
I'll check.
You wouldn't have a SERVICE manual parts assembly
diagram would you of the pump?
 
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Made time to hand Fab a FLUSH attachment hose. Flushed the motor and water came out like it's supposed to so I figured it's not blocked.
Started the motor again and it ran rough the first min but smoothed out
after that and water finally came out of the tell tale but not at
full pressure.
Now I am convinced the AFTERMARKET impeller is no good so
I ordered another one.
It shifted into fwd gear ok but would not go into reverse so
I need to check that out.
I'm sure it will be a good motor when I'm finished.
 
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