Mercury 150 Black Max ~1992 year model

scout-j-m

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My dad recently purchased a 1992 ProCraft 180V fiberglass fish and ski boat. It came with what I assume is the original matching outboard - a Mercury 150 Black Max. Serial number is 0D145256. Against my advice he bought it without doing a compression test nor an on the water test and they just ran it on muffs, however, the boat and motor are both very clean for their age and I know fish and ski rigs often don't get much use since they don't do either well the allure can tend to wear off quickly. Anyways, I suggested we check compression, spark, and drain the fuel tank at least but my dad just wanted to go lake test it so I basically said your boat/money...your call and off we went. It actually ran very well aside from dying a couple times at idle after letting off throttle at low rpms and the tell tale stream seeming very hot compared to the smaller outboards I'm used to.

Performance wise, we were able to trim it out to about 5700 rpms at 45mph at WOT. Prop is a Quicksilver aluminum 19 pitch. I tried running these numbers but I can't find a definitive answer on the gear ratio for this outboard. I have seen 1.78, 1.87, and 2:1. I'm leaning to it being 2:1 because those other ratios would equal a ton of prop slip. Even at the 2:1 its still about 13%, which may be normal - I have jon boats with smaller motors in the 25hp range and I see more like 5-7% slip.

Could anyone help me out on the gear ratio we have, what our WOT range should be, and what model this would be considered (2.0L? XR2/4ect?)? Anything in particular to watch out for on this motor? Forgot to add oiler is deleted so its premixed. I want to help him do a full service on it including lower oil, lower pressure test, new impeller, compression/spark check, new plugs if necessary, fuel filter, add fuel water separator, and run some ring free or similar additive through a couple of tanks. I'm going to order the factory service manual for it as well.
 

Chris1956

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It is likely 2:;1. Easy to tell, simply turn the flywheel 2 complete turns and see what the prop does.

Replace the waterpump impeller, wearplate and 2 gaskets. Replace the pump cover if it has a scratch. Replace gear oil and check spark plugs for wear. it should have gapless sparkplugs.

It likely makes sense to replace the thermostats as well. Make sure the overheat alarm works. Ground the brown wire that goes to the cylinder head and listen for alarm, ignition on.

Your speed sounds about right for an 18 footer w 19P prop.
 

scout-j-m

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It is likely 2:;1. Easy to tell, simply turn the flywheel 2 complete turns and see what the prop does.

Replace the waterpump impeller, wearplate and 2 gaskets. Replace the pump cover if it has a scratch. Replace gear oil and check spark plugs for wear. it should have gapless sparkplugs.

It likely makes sense to replace the thermostats as well. Make sure the overheat alarm works. Ground the brown wire that goes to the cylinder head and listen for alarm, ignition on.

Your speed sounds about right for an 18 footer w 19P prop.
Appreciate the reply. I'll check gear ratio manually like you said...should be easy if its 2:1 and only require two turns vs 10.

Do I need to check the poppet valve? I dont have any experience with them. Do they simply open at higher rpms to make sure there is increased waterflow, in a way bypassing the thermostats?
 

Chris1956

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Yes, The Poppit opens at a certain water pressure (about 2000RPM), causing most cooling water to bypass the thermostats. Thermostats must open for you to have a telltale, on that motor. Underway you should always have a telltale.

if she doesn't overheat the poppit is likely fine. if you need to work on the poppit, make sure you get exact poppit kit for your year motor, as they changed over the years.
 

444

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Jul 16, 2010
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150hp's came with a 2:1 bottom end. Your speed sounds about right.

It will cost a bit but replace the thermostats, poppets, spark plugs, water pump kit and do a link and sync as per the factory service manual (I can't stress enough how important a correct link and sync is on these engines). Dump the oil in the bottom end and check for water intrusion. On the muffs don't be surprised if the pee hole barely dribbles, this is normal. Even in the water it's not a super robust pee stream on these and yes it will get warm. I would also do the fuel filter and water separator as well as a fuel pump kit and new rubber hoses and clamps. Assume the previous owner neglected it and give it a good once-over, it is knocking 30 years old after all.

Service manual download:

 

scout-j-m

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Messages
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150hp's came with a 2:1 bottom end. Your speed sounds about right.

It will cost a bit but replace the thermostats, poppets, spark plugs, water pump kit and do a link and sync as per the factory service manual (I can't stress enough how important a correct link and sync is on these engines). Dump the oil in the bottom end and check for water intrusion. On the muffs don't be surprised if the pee hole barely dribbles, this is normal. Even in the water it's not a super robust pee stream on these and yes it will get warm. I would also do the fuel filter and water separator as well as a fuel pump kit and new rubber hoses and clamps. Assume the previous owner neglected it and give it a good once-over, it is knocking 30 years old after all.

Service manual download:

I found a digital copy of the manual I ordered but it's revision 2 opposed to the original rev I ordered. Oh well, I prefer a hard copy myself but the digital one will come in handy.

I plan to go through everything you mentioned. I noticed the manual was very adamant about keeping the forward idle 750 rpms or less. I also noticed the idle timing was very broad - like 2 - 9 deg ATDC. I'm used to seeing a tighter tolerance of more like 5 +/- 1 deg but maybe it's just my lack of experience with motors over about 50hp. But anyways, I'll check all of that and verify with my timing light on the water.

I need to check the overheat warning system asap as that will go a long way into feeling confident in the motor on the water. The boat does not have water pressure or temp gauge so I will have to figure out where the buzzer is located. Anyone happen to know if the CDI has a rev limiter for when the temp sensor is triggered?
 

Chris1956

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The RPM is not limited if the motor overheats.

Usually those motors have a temp sender for a gauge on one head and an overheat sensor on the other head.

The overheat sensor will ground when the motor overheats, sounding the alarm. I would turn the key on and jumper both to ground and see which one is overheat and if it works correctly.

The buzzer is usually located in the controls, but can be mounted externally if necessary.

A water pressure gauge is a real good idea.
 

scout-j-m

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The RPM is not limited if the motor overheats.

Usually those motors have a temp sender for a gauge on one head and an overheat sensor on the other head.

The overheat sensor will ground when the motor overheats, sounding the alarm. I would turn the key on and jumper both to ground and see which one is overheat and if it works correctly.

The buzzer is usually located in the controls, but can be mounted externally if necessary.

A water pressure gauge is a real good idea.
Yeah, the water pressure gauge is high on my priority list. This outboard will be used primarily on Lake Guntersville in Alabama which is a great lake and fishery but that's in part due to the massive amounts of eel grass and other vegetation. If anywhere aside from the main channel you constantly run into patches of grass which will catch on the lower and cause ventilation issues and no doubt block the water intake at least to some degree.
 

Dukedog

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over temp sensor is right below #1 spark plug.. will be "one" tan or tan/blue wire.. temp gauge (was an option on that motor) sensor will be a "two" wire sensor right below #2 sparkplug.. tha idle timing can vary quite a bit when first starting after complete linc n sync.. "finale" idle timing/rpm/speed is set with idle timin' screw only with rig in tha water, in gear.. (per OEM manuals) degree number won't mater... there is nothing on that motor for any type protection except tha "warning" buzzer for over heat and/or oiler... nothing to shut it down and/or limit rpm..

water pressure gauge can be your best friend..

this is justa suggestion.. a motor that age and NOT knowin' tha background of it you may be ahead by removing tha oil injection and going ta pre-mix.. lotsa folks blame tha so-called "plastic gear" as its weak point.. it is if tha motor has been overheated at anytime.. an item most don't know about and/or leave out when bitchin' about it... jmo.
 

scout-j-m

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Joined
Jul 31, 2009
Messages
601
over temp sensor is right below #1 spark plug.. will be "one" tan or tan/blue wire.. temp gauge (was an option on that motor) sensor will be a "two" wire sensor right below #2 sparkplug.. tha idle timing can vary quite a bit when first starting after complete linc n sync.. "finale" idle timing/rpm/speed is set with idle timin' screw only with rig in tha water, in gear.. (per OEM manuals) degree number won't mater... there is nothing on that motor for any type protection except tha "warning" buzzer for over heat and/or oiler... nothing to shut it down and/or limit rpm..

water pressure gauge can be your best friend..

this is justa suggestion.. a motor that age and NOT knowin' tha background of it you may be ahead by removing tha oil injection and going ta pre-mix.. lotsa folks blame tha so-called "plastic gear" as its weak point.. it is if tha motor has been overheated at anytime.. an item most don't know about and/or leave out when bitchin' about it... jmo.
Thanks for the advice. This motor has already had the oiler deleted which is how I prefer it as well.
 
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