Old Merc needs all your wisdom and knowledge

[Mercnewguy]

I just bought my first little bass boat and this old motor came with it. Before I send it on and start looking for other motors I want to see if it works. First its a Mercury Blue stripe no idea what year or HP but the model number is 3751876. Can anyone tell me what model it is? Next I tested its compression and the cylinders are all at exactly 65... Not the greatest but how bad is this news? I'm pretty sure this motor was taken off another boat then placed on this one. It was never hooked up and the power cable from my boat controls that is supposed to plug into the side of the motor has an 8 pin configuration, male. But the motor has a male configuration also... MOST IMPORTANTLY I want to know if I can bypass not having the cable going up to the ignition at the key (since I don't have it) and just start the motor from the back and keep it running.

It looks like all the wiring on this old motor has been replaced not too long ago. The wiring harness is in great shape as well as everything else. Also looks like a new distributor was placed on it. Spark plugs look brand new. Only problem is that compression and the lack of the power cable running up to the front of my boat.

Any tips on how to jump start this guy and keep it running from the back end would be appreciated. Thanks in advance for all your wealth of wisdom and knowledge and for helping out this new guy to boating.

 

[Laddies]

Re: Old Merc needs all your wisdom and knowledge

Thats the serial number look on the starboard side of the block for a pad that has, thunderbolt, panther, marathon six or something like that and with that and the serial numbers we should be able to help you.

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge

Thats the serial number look on the starboard side of the block for a pad that has, thunderbolt, panther, marathon six or something like that and with that and the serial numbers we should be able to help you.

Thank you for your reply and help, I will look when I get home tonight. Where on the block is it? Is it easy to see or do I have to remove some of the cage? Thanks!

 

[Laddies]

Re: Old Merc needs all your wisdom and knowledge

Ussually is about 2/3 of the way down from the top on the 4 and 6 cyl model you could also include the number of cyls.

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge

These are some photos of my motor.

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge

Here are some photos of the power connections. The 7 with one in the middle is coming from my boat and the 6 plus one in the middle is the one on the motor. Is there any way to adapt these two together or do I need a whole new power cable? Thanks in advance for your knowledge and patience.

What kind of motor was on this boat before that took that kind of power cable?

 

[Laddies]

Re: Old Merc needs all your wisdom and knowledge

It's a 73 1150 or maybe a 74 1500 get the name off the engine block and the carburetor numbers

 

[Laddies]

Re: Old Merc needs all your wisdom and knowledge

Your engine is battery powered CD and the harness you have is for a alternator powered CD. I will have to check to see if there is a simple way to adapt the 2 I think not as a first thought.

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge

Your engine is battery powered CD and the harness you have is for a alternator powered CD. I will have to check to see if there is a simple way to adapt the 2 I think not as a first thought.

Thank you! It is a little old bass boat. Does the 65 compression worry you? Its been sitting for a while do you think if I fed a little gas, oil and seafoam in there and let it sat it would free things up and get better compression? I thought it was odd that they were all exactly 65.

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge



This is all I found on the starboard side of the motor

 

[bgc]

Re: Old Merc needs all your wisdom and knowledge

Going off the serial and block part number, this is indicating a 1500, 150 hp.

Mercury Marine Model 1500 150 HP CYLINDER BLOCK AND CRANKCASE ASSEMBLY Parts

Treating the piston rings with Sea Foam can help restore compression if there is a build up.
Use caution with the electrical system. Try to find the correct wiring harness to do a test start, switch boxes, stators, triggers and other components get expensive for this old gal.

 

[brnschoneck]

Re: Old Merc needs all your wisdom and knowledge

to test it u can hook up a battert with a starter weitch to the pos.. terminal on should be left side of starter and ground , make sure u hook up muffs youll probably need to do the impellar if its been sitting ... you can also try some miracle oil in the cylinders let it sit for a few hours to loosen some up and add a little to ur gas with ur regular two-stroke oil ... Dont be suprised if you have idling problems or bogging at full throttle you may have to do a carb rebuild 3-4 hour job !!! i bet you after this she"ll purr like a kitten !!!These are just some regular things with these motors if they been sitting ...I have two 65 65 hp i had to do this too ...Compression is a little low however if its they same or with in 10psi in all cylinders she'll be ok I think !!!!

 

[turtles11756]

Re: Old Merc needs all your wisdom and knowledge

first off hold off on looking for a new motor you have a monster of one right there ! what kind of gauge was used checking compression ? 65 on all six don't jive you need a gauge screw in with a flexible hose to reach the bottom hole (don't crossthread). the wiring inside was redone because all the original wiring rotted away very common on the old mercs. check comp. again now look for the correct control box with the correct plug end for that motor ebay and craigslist all the time and hot right now. get a merc service manual, check all fuel lines, take your time, and hold on when it fires

 

[Laddies]

Re: Old Merc needs all your wisdom and knowledge

If you can not find a used harness in good condition here's a link for a new one. Mercury / Mariner Wiring Harness: 474-9550

 

[calvinator]

Re: Old Merc needs all your wisdom and knowledge

MERCURY OUTBOARD MODEL YEAR GUIDE 115 HP - 150 HP -- Mastertech Marine

Your S/N indicates a 1973 Merc 1500 - 150HP. Nice motor, powerful and easy to work on. I just bought a 1975 150 motor that I'm working on.

I have the service manual. Anything less than 80 PSI says you need to rebuild. Seeing all cyl are at 65 PSI, I would recheck the compression with a better tool. Should see around 120psi on the cylinders.

 

[Laddies]

Re: Old Merc needs all your wisdom and knowledge

If you want to see if the engine will run with out the harness, hook it up to some water and use a fully charged battery and good jumper cables, hook the positive to the input side of the solinoid and the negitive to a good ground, it's important as low or high voltage can kill the switch box and a bad cable connection can fry the rectifier with the engine prelubed with powertune or seafoam hook a small jumper between the red and white terminal 4 terminal side of the switch box this will give you a ign. circurt to run or check for spark then just use a jumper between the positive and the yellow terminal on the solinoid to turn it over. Here's a wiring diagram if it will help you.

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge

Thanks everybody I really appreciate all this. This forum is great. Where would you all suggest getting the manual? Is there a cheap PDF download online anywhere from a reputable site? When testing my compression I used a OEM compression gauge and after taking out all the plugs I just hand tightened it in to place. It sets down in the block just enough that I could not get a wrench or socket on it to get it tight. Do you think hand tight was not enough and throwing off readings? turtles11756 looks like someone was nice enough to drill out a nice size hole in the back so I was able to stick my socket in there and pull out the bottom plug no problem and stick the compression tester straight through without bending the hose to much. So you fellas think it still has some life left to give yet eh? I will hunt around for a harness.

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge

Thanks Laddies. Let me make sure I understand. So instead of jumping it straight at the starter with the ground on that top strap and the positive on the bottom, I should put the positive on the red nut there on the starter? Then I will hook a wire between the red and white nuts on the left side of the switch box in that diagram. Then I willl run a wire from the red on the starter solenoid and touch to either the yellow on the starter solenoid or just go right up to the starter? Everything I say correct?

 

[Mercnewguy]

Re: Old Merc needs all your wisdom and knowledge

Also does anyone have the order of the spark plug cables from the distributor to plugs handy? On my 3 and 4 plugs there are numbers "3" and "4" on them but they were reversed in the wrong spot... So I want to be sure they are where they need to be.

 

[Laddies]

Re: Old Merc needs all your wisdom and knowledge

1-4-5-2-3-6 Yes you understood me right it has to be done that way to supply 12 volts to the switch box red terminal