governor effect

[ALX357]

Casey, et al.
Mercury 50hp ser.# OG026028 two-stroke
I think it is a "Mercury Classic" - parts guy at dealer told me motor is somewhere in early 90's mfg. date. ( cf. boat is 2000 model )
Some one suggested i check my high-speed advance setting, - does this sound reasonable / likely ?
....the general look of the carb throats is squeaky clean, no gunky build-up, but i haven't yet tried any cleaning / probing.

[Catigale]

If your ignition timing isnt advancing as designed you would have good low rpm performance but no top end performance as you describe, so its worth checking out.

If this is electronic ignition though, I would rate that possibility as near zero - they work pretty digitally (either perfect or not at all)

Problem is getting access to the tools (diagnostic meter) you need to troubleshoot something like this..

[ALX357]

early nineties.... possibly just electro-mechanical advance, ? maybe Casey could tell us from my serial number above.

[Catigale]

Thanks ALX357 ...I missed the early 90s part

I would guess mechanical advance

[Casey]

AlX357

Looking at my Clymer chart, starting serial number for the 50hp original model for 1994 was 0D279350. The starting serial number for 1995 was 0G117236. That indicates to me that your engine was either a 1994 or 1995 original model. The ignition system for serial number prior to 531301 is AD-CDI with mechanical advance. After serial number 531301, it is a CDM system with mechanical advance with an RPM limit module.

AC-CDI= alternator driven capacitor discharge ignition
CDM= capacitor discharge module

[mtc]

I just rebuilt a Webber two bbl last weekend. Theres not much to them, but its all gotta be exactly right. This one I did was missing internal parts, the float bowls were bent all to hull, the springs were flattened its amazing this Jeep was running at all.

My point is that just because its on the engine doesnt mean the carbs to spec. Not that Im recommending that you rip the carb(s) off, but do you know someone else didnt? Fuel is one of the most important components of generating HP. Ignition is pretty straightforward its there or its not. Air is critical, but easy to verify.

Fuel? Well, thats another story. Not enough fuel, not enough hp. Too much fuel, not enough hp. Gotta be just right. Thats why injection is so perfect. Im an old Holley man and Id never go back.

Here're some reasonable steps to diagnosis this.

1. As a two stroke, the engine has an exponent ional HP curve climbing dramatically at higher RPM. As lower rotations, the engine will be a dog.

Verify that the:

2. Mechanical settings of cables, belcranks, stops, etc. are to spec.
a. Trust no one. Check it yourself. All these checks are easy and just take a little time and a usually a drill bit.
3. Butterflies are open (you've done this I think).
a. What did the venture bore look like?
4. Carbs are synchronized if there is more than one.
a. Causes an unbalanced condition and uneven bearing loads not to mention less fuel than spec.
5. Fuel flow rate is to spec.
a. Need to make sure your pump is ok, fuel lines ok, and fuel path clear.
6. Jets are appropriately sized and not gouged.
a. If you scratch the interior of the jet, you will ruin the spray pattern and need a new jet.
b. It's strongly recommended to only insert a machined ream identical in diameter to the ID of the Jet - and only with a skilled hand.
7. Plugs are appropriate and the proper heat range.
8. Compression is balanced to within spec % across the bank.
a. Two strokes are notorious for experiencing a partial seize. There may be scoring on the cylinder walls, which may show on a comp test.
b. Or, there could be a broken ring.
9. Exhaust flow is not restricted.
a. If the exhaust is not flowing, the engine will not be able to breathe and produce rated hp.

The octane shouldn't make a difference from 87 to 89. Im a novice to which prop works on which engine, but the physics of it is clear. Before you spend a lot of money on props, it would make sense to ensure that the prop shaft is capable of spinning at the correct RPM.

Certainly, if your boat is too heavy, its impossible for the engine to spin to max under excessive load from a prop with too big of a bite. This was shown when you changed to a less aggressive pitch, your RPM increased. Continue to reduce the props bite and your rpm should increase proportionately.

On the other hand, if you go too shallow, you will make a lot of noise and not really go forward at all.

Doing the math, what speed would you expect with this engine producing max rpm with the different props?

You may be right that this engine would be happier on the transom of a smaller, lighter, planning hull.

Michael

[ALX357]

yeah happier.... BUT HEY, the Mac was designed for a 50 HP motor, the Merc. 50 i have fits that bill, and there are plenty of others out there that have this combination, NO ?


Where are those owners with the X boat and Mercury 50 hp 2-stroke's ??

DO you get the "redline" ( 5000~5500 RPM ) and the speed ( I am guessing it should be about 17 MPH with an average load of 2 adults, 10 gallons water, 18 gallons gas, no ballast, and some boat-load stuff.)
Hello, please come in...... this is an old thread, resurrected...
note, my timing has been checked and a marine mechanic told me he thinks my motor is maybe mounted too low...
SO which holes are you using on the motor for the top ?? or how far above the transom is the top of the motor's mount plate....
REALLY, any additional information would be a great help, and note that this thread already has alot of background info on my motor, conditions, power problem, rev's, props, etc.

[bobmonroe]

Your mechanic may have hit it, check your manual, usually the cavitation plate should be within 1" from the keel or bottom of the boat. If the motor is too low, lot's of spray. Too high, over revving"cavitating". I had to raise my 50 ETEC 1-1/2". Use a strait edge to check it.

[ALX357]

Bob, (and any others who might have been there.....) exactly what was your motor doing before you raised it 1-1/2 inches ... ?? apparently it is fixed now, but were our problems similar, and is your motor now running rev's in its powerband at WOT, and are you getting 15-20 MPH ??

[Catigale]

ALX - I think most of the with 50HP have the Bigfoot motor, which has a different transmission than the classic 50 HP.

All bets are off comparing WOT, rpms, HP etc.

[bobmonroe]

ALX, When the motor was mounted too low there was a lot of spray
around the motor, kinda like a water skier that couldn,t get up. After I raised the motor and changed the prop to a 14D x 13P it now does 21mph statute. It was not easy to do, you can probably get it done for about one hour labor. Bob

[ALX357]

Bob, thanks.....
... and so besides the spray around the motor, the boat was not getting full speed, and your rev's at WOT were not up high enough, say betwen 5000 and 5500 RPM ?
1=1/2 inch ... could be that is it...

[ALX357]

even 'though most Merc 50's on the X-boats are BigFoot motors, with over 5000 Mac26X's produced, and 915 users registered on this board, there must be several MacX owners with Classic 50 motors who are visiting here currently and can add information on this ....

[Casey]

ALX357

I apologize for not checking the board more frequently. I have the classic 50 mercury. Under the loaded conditions you describe, with bottom paint, I get about 18-19mph in calm conditions per gps with no current at 5500 rpm. I believe that bottom paint is responsible for a 2mph reduction, but that was prior to obtaining a gps. If you have barnacles, even a few, it will drop your speed dramatically.

I will check the depth placement when this storm blows over.

[ALX357]

Casey, thanks, and that's what i thought, about the potential performance of the Classic 50....
.....also if you would, what prop are you using, size and pitch and blades, 3 or 4 , type, etc. ??