Mercury Black Max 150 to 175 conversion?

[Rowroy]

I'm thinking about buying a 20' bowrider that's powered by a 1991 or 1992 (can't recall at the moment) Mercury Black Max 150. The owner told me that the engine has been "jetted up to a 175". Therefore, in his mind, it's a 175.

Is this even possible? I would think "jetting it up" would just make it run richer, with no real gain in performance (possibly even a loss in performance).

He also stated that it "runs a little rich at idle because of the oil injection" (which is still intact). I thought the oil injection leaned out the mixture to 100:1 at idle. Is this incorrect?

The weather here has been too cold to take the boat out on the water, so I haven't actually seen it in action.

Any help would be greatly appreciated.

 

[xxturbowesxx]

Re: Mercury Black Max 150 to 175 conversion?

ive never heard of "jetting" a motor to anything. You can change Reeds,shave heads,port and change out exhaust tuners but unless you have an XR4 motor then i have no idea what this guy is talking about. the XR4 blackmax was a 150hp that was grossly underrated for hp during the 150hp race from all the manufactures. Its more like a 160-170 but advertising a 150 as a 175 seems bogus unless he has had it on an engine dyno. Call the guy and ask him to be more specific.

I would also remove the oil injection and premix. I dont trust those things and ive heard to many horror stories.

 

[Chris1956]

Re: Mercury Black Max 150 to 175 conversion?

Rowroy, You can go on the Crowleymarine.com website and compare the part numbers for the '92 150HP and 175HP, to see what parts they shared. First check is to see if they have the same displacement. My '93 Merc 135V6 is a 2.0L motor. I think my 135HP shares displacement with the 150HP. The 175HP may be the 2.4L block.

If they are the same displacement, you can compare blocks, heads, reeds, pistons and carbs. It is likely the blocks and carbs are unique to each motor. If so, the 175HP block will have porting differences, which give it the extra power.

 

[Faztbullet]

Re: Mercury Black Max 150 to 175 conversion?

If its a plain ole 150 it is a 2.0 liter, Xr6 is a 2.5, and Xr4 is a 2.4 liter. You are correct its just burning more fuel with no gain.The running rich at idle could be clogged bleed restrictors or idle jets/needles been messed with.

 

[LOW-LIFE]

Re: Mercury Black Max 150 to 175 conversion?

If its a plain ole 150 it is a 2.0 liter, Xr6 is a 2.5, and Xr4 is a 2.4 liter. You are correct its just burning more fuel with no gain.The running rich at idle could be clogged bleed restrictors or idle jets/needles been messed with.

what years were the diferant motors made?

 

[Rowroy]

Re: Mercury Black Max 150 to 175 conversion?

Yeah, I'm going to look into this a little further. The owner doesn't know much about boats and he tends to give somewhat vague answers to specific questions.

I don't care if it's just a plain ol' 150; I just don't want to here some BS story about new jets adding a 17% increase in performance.

 

[xxturbowesxx]

Re: Mercury Black Max 150 to 175 conversion?

what years were the diferant motors made?

xr4 ended in 91(i think it started in 87) and xr6 took over from there. the xr4 came with a smaller lower unit that caused less drag but is weaker than a standard lower and has limited prop sizes assosiated.

 

[Faztbullet]

Re: Mercury Black Max 150 to 175 conversion?

2.0 lite 150: 1979-1991 years -no finger ports in block
2.0 liter 175 1976-1981 years- no finger ports in block
2.0 lite 150: 1992-2000 years- finger ports in block
2.4 liter 150 Xr4 1985-91 years- steel sleeves and finger ports
2.5 liter 150/Xr6 1991 year- bottom guided rod and finger ports
2.5 liter 150/Xr6 1995-2002 years -top guided rods and finger ports
The Xr6 also came with the small(Inline) gearcase but has a different casting and driveshaft and pinion bearing. The early 1979-88 motor the only difference between 150-175 is the carbs and advance box. All other parts the same.

 

[hkeiner]

Re: Mercury Black Max 150 to 175 conversion?

Unless one just has to have the extra horsepower, it seems to me that a more important consideration for buying that 150hp motor is it's general condition ... such as good compression and spark on all cylinders, no water leaks into the lower unit, overall appearance, etc. Just my thoughts.

 

[j_martin]

Re: Mercury Black Max 150 to 175 conversion?

I wouldn't believe a thing he says. Everything he's given you so far is Bright and Shiny.

That said, if you take along a compression gauge and verify it has good compression on all cylinders, and spark at all cylinders, everything else can be fixed pretty easily.

If you get it, plan to get an OEM service manual, and spend a honeymoon period getting to know the motor and all it's adjustments. Check everything as it sounds like this joker might have been "fine tuning" it with no knowledge. That is the general prescription for a grenaded engine.

hope it helps
John

 

[Rowroy]

Re: Mercury Black Max 150 to 175 conversion?

Yeah . . . One thing that this guy told me that I do believe is that the water pump hasn't been changed since he bought the boat . . . 10 years ago. He does have a receipt from a reputable marina for a tune up last year, but to be honest, that's of little comfort.

 

[Rowroy]

Re: Mercury Black Max 150 to 175 conversion?

I forgot to mention that I will be testing the compression and spark, as mentioned above.