How to choose an old 2-stroke 150/175 Merc

[Dukedog]

yeah.. in some circles tha down housing is refered to as tha can and tube as tha liner.....

 

[Dukedog]

if tha "tube" is not removed then tha holes won't mater (noise!).. all ('bout 98%) exhaust would exit thru tha hub....

 

[BWR1953]

Butchery, that is all it is. I doubt it even adds 1/10 mph

Uh, thanks for that. I guess.

 

[BWR1953]

Anyway, the XR6 that I bought has been in solid, good service with the prior owner for 13 years. And still many more years before that from the owner he got it from, so, I'm happy with it.

 

[Chris1956]

Normally standard dino gear oil is fine for those older gearcases, as that was all there was at the time when new. You might consider synthetic gear oil as the smaller gearcases like yours are a bit challenged by the power of the XR6.

 

[Dukedog]

Chris is correct... jus don't "baby" it when ya put it in gear.. will help with its longevity... when coned and tabbed its tha choice of racers by far.........
glad ya happy with it........ should last ya a very long time.

 

[That old Mercury]

I'm in "search mode" for a used 2-stroke 150-175HP Mercury, possibly 2, but just one at a time. I choose Mercury partly because I'm a fan, but also because the only repair shop in my area is for Mercury. Logistics is a factor for me.

I've been doing a broad search, a ton of reading and watching videos online. I'd get fired up about one year-group, then read that those were not good. Or some such. My local Mercury repair shop steered me away from a few as well. I definitely don't want anything from the 70s or early 80s. That puts me in the range of mid-80s up to about 2007.

One thing that I do in my research is to check parts availability, either aftermarket or OEM for a motor I find interesting. That can be a major factor. I was seriously revved up for a Merc XR4, only to find that a voltage regulator is $800! That was a bummer. From what I'd read, the XR4 was designed for bass boats (music to my ears!) and actually had an output of 170-180HP. Glorious!

I'd been interested in the 1990 year(s) EFI versions, but my repair guy said to steer clear because of electronics failures and parts availability.

And another factor for me is saltwater. I'm a bass angler, so don't go into the briny deep. This being Florida, there are loads of engines which are used in saltwater and owners always advertise them as "flushed and washed" after every trip. Uh huh.

Any suggestions on which engines may be best? Things to watch out for? Would an XR6 work? I've read that it's rated closer to 170HP as well

All help appreciated.

I have a 1984 , 150 hp black max.
Parts are available and fairly cheap.
I have replaced the stator, trigger, cdi boxes, water pump and so on.
Compression 125 psi on all cyclinders. Just hard to crank when the temp is below 40 degrees unless you have the fast idle in a certain place.
On a 17' hydrosports bass boat with 4 batteries and tank full of gas with 1 person and all gear it will run 50 mph on gps.
I would go with a newer motor myself and from living in Fl for 40 years do all you can to avoid salt water motors . I have seen so many motors of all kinds that people just dont flush out or dont flush long enough .
I know a lot of them ! Some say it ran in brackish water so its good!
Good luck

 

[BWR1953]

if tha "tube" is not removed then tha holes won't mater (noise!).. all ('bout 98%) exhaust would exit thru tha hub....

Got it, thanks.

 

[BWR1953]

I have a 1984 , 150 hp black max.
Parts are available and fairly cheap.
I have replaced the stator, trigger, cdi boxes, water pump and so on.
Compression 125 psi on all cyclinders. Just hard to crank when the temp is below 40 degrees unless you have the fast idle in a certain place.
On a 17' hydrosports bass boat with 4 batteries and tank full of gas with 1 person and all gear it will run 50 mph on gps.
I would go with a newer motor myself and from living in Fl for 40 years do all you can to avoid salt water motors . I have seen so many motors of all kinds that people just dont flush out or dont flush long enough .
I know a lot of them ! Some say it ran in brackish water so its good!
Good luck

Check post #51.

 

[That old Mercury]

My Bad !
Post was still going so i thought it was still going.
My posts can be deleted , its no problem.
Sorry

 

[BWR1953]

My Bad !
Post was still going so i thought it was still going.
My posts can be deleted , its no problem.
Sorry

No worries!

 

[BWR1953]

Normally standard dino gear oil is fine for those older gearcases, as that was all there was at the time when new. You might consider synthetic gear oil as the smaller gearcases like yours are a bit challenged by the power of the XR6.

Thanks Chris. I plan on doing the water pump and a fresh gear oil change anyway, so I'll switch to synthetics.

At 71, I remember those old Sinclair commercials about dino oil.

 

[BWR1953]

Chris is correct... jus don't "baby" it when ya put it in gear.. will help with its longevity... when coned and tabbed its tha choice of racers by far.........
glad ya happy with it........ should last ya a very long time.

Coned and tabbed?

 

[BWR1953]

...do all you can to avoid salt water motors . I have seen so many motors of all kinds that people just dont flush out or dont flush long enough .
I know a lot of them ! Some say it ran in brackish water so its good!
Good luck

I definitely avoid the saltwater motors. Heck, I saw one ad in Key West where the seller stated that his engine was run in freshwater only!

 

[Dukedog]

Coned and tabbed?

hot rod thing!.. 80+ mph... its tha fastest production gear case merc made... sumin' you don't need....................

 

[BWR1953]

hot rod thing!.. 80+ mph... its tha fastest production gear case merc made... sumin' you don't need....................

Ahh... I feel the need for speed!

My old Winner bass boat clocked 72MPH GPS with me alone and 68 with my big cousin on board.

 

[BWR1953]

... there will be a build date stamped on tha port side block half as well.. if not on tha flange it will be on tha block half at base of number 2 cylinder.... that will tell exactly what year it is..

Found it! Looks like the engine was built on Jan 6, 1992. That means it's the original engine on this 1992 boat. 34 years old and still strong! Thanks again!

 

[Chris1956]

You can check out the forums on the scream and fly website where they discuss "dry stacking".

The thing to remember is that 2 cycle engines like some backpressure at the right time in the exhaust cycle. This is the principle of expansion chambers. With the right expansion chamber, at the right RPM, at the right time in the exhaust cycle, the backpressure pushes some of the unburnt (scavenging) fuel mixture back into the cylinder, after or just before the transfer ports close. This boosts power and saves fuel. It is one of the benefits of "loop charging" the engine.

However, OBs usually have the exhaust thru the prop which reduces backpressure. The OB's tuner can have some expansion chamber effect.

The eTEC motors had an exhaust system with a fancy exhaust tuner and a diverter valve. The throttle postion controlled the diverter valve, which caused the tuner to act sorta like two different length expansion chambers, providing a power boost at two distinct RPMs.

 

[BWR1953]

You can check out the forums on the scream and fly website where they discuss "dry stacking".

The thing to remember is that 2 cycle engines like some backpressure at the right time in the exhaust cycle. This is the principle of expansion chambers. With the right expansion chamber, at the right RPM, at the right time in the exhaust cycle, the backpressure pushes some of the unburnt (scavenging) fuel mixture back into the cylinder, after or just before the transfer ports close. This boosts power and saves fuel. It is one of the benefits of "loop charging" the engine.

However, OBs usually have the exhaust thru the prop which reduces backpressure. The OB's tuner can have some expansion chamber effect.

The eTEC motors had an exhaust system with a fancy exhaust tuner and a diverter valve. The throttle postion controlled the diverter valve, which caused the tuner to act sorta like two different length expansion chambers, providing a power boost at two distinct RPMs.

Thanks Chris. I'm just going to run the thing the way it is now. It's been working well for 34 years, so I'm not changing it. Besides, I can't do much nowadays anyway.

I remember running tuned pipes on my RC airplanes 50 years ago. You could really tell when the prop started to unwind and the engine got "on the pipe" and started really screaming. I had one race plane that could go 140MPH. Alas, my reflexes and eyesight aren't good enough to do that anymore.

Guess I'll just go fishing!

 

[Chris1956]

Yes, I had a 360cc enduro dirt bike some years ago. She had real good power at all RPMs, but if you kept the RPMs near redline as you accelerated, the power was incredible. Of course, with the dinky electrical system she had, you would melt the battery and burn out all the lights at high RPM.