Trying to determine Mercury Black Max power head and upper unit serial numbers

[seneca95]

I have been trying to determine the serial numbers on my Merc. outboard. The upper unit seems to be a 150HP Black Max XR2 #159 0-8334 D. The jack plate number is 6636823. The power head soft plug says 175. The heads both have 15221-c2 marked down the side and 1 06 95 stamped in the top. The case has 3 14 95 stamped in it near the top.

According to the last owner, the power head was changed by the prior owner. He had it tuned and ported. New boat to me and like to know all the ins and outs. Like to get manuals and power curve charts to dial in larger prop on Switzer sk-175. Comes out of the hole in a heartbeat. Propped with Merc. trophy plus 21p. Pulls skier and tubes great but want to get the top end dialed in for some fun.

 

[jerryjerry05]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Stbd side(right) there is a shiny silver plug.With a number engraved in it.Should start with OG or something like that, then 6 numbers.
What RPM at wot?J

 

[j_martin]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Actually, XR2 would likely be in the A - C range. I would suspect he has a 175 power head, maybe ported a bit and with heads shaved to up the compression.

Clues for setting it up would be
1. The carbs on it, and jet sizes, especially main jets.
2. Compression, with an accurate gauge and noting elevation and atmospheric pressure at the time.
3. Pictures of the block and heads, for a clue as to displacement. If you've had a head off, cylinder bore would tell.
4. Are the reed blocks vertically or horizontally oriented.

With proper base plate and gaskets, any 2.0, 2.4, or 2.5 powerhead will bolt right onto an XR2.

It's a frankenmerc. casting/serial numbers aren't going to help much.

 

[Faztbullet]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

The head casting(15221-c2) makes it a 2.5 block. The date stamped in top of block and 175 in soft plug is usually a rebuilders/reman build date and hp. You can look at the crankcase halves behind throttle arm to get Merc's manufacture date of block. As for tuned and ported, if its a reman head they leave factory porting in place.

 

[seneca95]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers




Thanks for the info. The last post seems to be accurate as to the head having been remanned. I have searched the power head pretty well. The numbers listed in the original post are all I can find. Attached are pics of the power head.

If my compression gage is accurate, all cylinders seem to be at 110 PSI at 700' above sea level and BAR 28.55". Lower than what I expected. I have used thGagege before on a PWC, and was in the 130 psi range. So, I think it is correct. This motor seems to have more power than my I/O Merc 4.3l Sea Ray of the same HP but with a lower top end.

As for the prop, I have a full vented Merc Trophy Plus 21p 4 blade that I run. Stays hooked up all the time. Great acceleration. The top end for this prop I believebeingeing rev limited at 6150 rpm at 53 mph (GPS). I tried a no nambladealde non-cupped 26p prop. I was at 5200 rpm at 55 mph (GPS). With the Trophy, at 40 mph and hit the throttle still has a lot of acceleration to the top end. My Sea Ray running a 4 blade 23p Com Prop, I could do about 64 (non GPS). This boat way acceleratesates the Sea Ray running a Alum. 3 blade 19p.

 

[Faztbullet]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

It a 2.5 block with: old style WH carbs, 16 amp ignition system,2 piece cowling, basically parts/ignition from a pre 89 motor on a later model powerhead.

 

[j_martin]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Would help to have the numbers off the top of any carburetor. There were many WH carbs, each a bit different but close enough to all take the same rebuild kit.

Damn, fazt, you have a sharp eye. I didn't see the rectifier in frame 5.

 

[seneca95]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

The carbs are WH-29 and then -1 -2 -3.

 

[seneca95]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Any suggestions as to what manuals that I should get? Good sources for HP/torque charts? I am new to large outboards, and always looking for good sources such as yourselves. Thanks for your help.

 

[Faztbullet]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Damn, fazt, you have a sharp eye. I didn't see the rectifier in frame 5.

Rectifier and black stator Wh-29 are 150 carbs so they must have jetted them up to work.

 

[j_martin]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Carbs are original XR2 for a 2.0 L vertical reed head. This head is more displacement and also horizontal reeds. I would guess it'd want about 30% more flow at WOT. Probably could use better carbs for the application. Bet it blasts out of the hole like a scalded dog.

The XR2 electronics don't limit it in any way except if whoever set it up put the advance module on it, take it off. If there's anything hooked up to the bias terminals except the jumper between the switchboxes, throw it away.

When you take your compression readings in the eye of a hurricane, they'll be a little low. looks good to me. I guess we'd need to know if it's finger-ported to tell what running compression would be.

I'm jealous. Looks like you have a winner.

 

[seneca95]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Being a newby to large outboards, where would I find the bias terminals? Also with the wh-29 carbs, would that be limiting my top end (like a restrictor for air mass flow)? It does scream out of the hole, but thought top end would be a little better. Any suggestions as to the proper size carbs to keep my eye out for this application? 1000 lb. boat used for tubing and cruising with usually 4 adults. Pretty boat with muscle to match.

 

[j_martin]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

There's 4 terminals across the top of each switchbox. The leftmost terminal is the bias terminal. It is supposed to be connected between the switchboxes with a white/black jumper. If there's an idle stabilizer or advance module, it will also be connected to that terminal. The idle stabilizer isn't needed if the engine is in decent tune, and the "advance" module, though advancing the timing a bit near top end, retards it severely at last (5500), limiting the pull at the top. Either one shorting to ground at WOT will throw rod caps at you.

Carbs off a 175 or 200 2.4 or 2.5 would move your power band up a bit. If the original XR2 tuner is in the mid, a 200 tuner would pick it up a bit at the top at the cost of a little hole shot.

I'm not real familiar with the various carbs. Perhaps Fazt could make a recommendation.

 

[Faztbullet]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Heres a good set off a Xr6(2.5) and good price also. This will get you close to where you need to be...
http://cgi.ebay.com/ebaymotors/Merc...7574209QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

 

[seneca95]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

The link is for wh-41 carbs off a XR-4 150 HP. Do I need carbs for a XR-6 175 HP power head, or are you looking at the combo of the jet size and throttle body size?

Thanks

 

[j_martin]

Re: Trying to determine Mercury Black Max power head and upper unit serial numbers

Although they all look the same, there is internal differences between carburetors. Rule of thumb is that the jetting specs go with the carburetor, with relatively minor differences between applications.

XR4 is a 2.4L hot rod vert reed 150 that puts out about 162 right out of the crate. They would probably work very well on your engine, but aren't noted for top end performance. If you want fishin motor performance, and your carbs have foam floats, jump on these, kit them, and throw them in.