2 stroke question

[wolf]

Apperently your not hearing what some very knowledgable people like bananas and pro have said both of these men have told you that running it low RPM will hurt your engine,Ive even told you what you may want to do but your ignoring what some are saying.
IFL who is a mechanic has told you as well.As with gunsmith.

This is not a waste of time we just dont want to see you BLOW UP your engine.
To maybe put it in easier terms for you say you go up the malahat staying in 5th gear of your truck it starts to knock and ping because your lagging it, drop it down to 4th and sound is gone and your running it the way you should not hurting it puring like a kitten.
You want to be in what the manufactuer has put forth and if it is 5000 to 5500 rpm then you should be inbetween those ranges plain and simple if you dont your asking for trouble.

Do whatever you want its not my boat I know what I would do.

Good luck to you.


wolf

 

[Charlie]

Lots of good advice given here, many years of experience being thrown your way! You should listen to them, as long as it doesn’t have anything to do with buying a larger prop with more pitch or trying to get your WOT up to 5800 RPM! Yea, I looked it up!

If you are getting 4900 RPM WOT, with a “full load”, you are fine and will not be doing any harm to your engine! Personally, I would still like to see it closer to the high side than right on the the low? Getting the tachometer checked is a good idea, if there is any question there? I wouldn’t trust a tach, even after it got checked! I have had so many of those things inaccurate and off – it’s not even funny. As I have stated before, it is the only way to get an accurate reading of your RPM and since you are running on the low side of WOT, that would be nice thing to confirm!

Have you ever noticed all those brand new outboard engines setting at a dealer – they don’t have props on them? Ever wonder why? They match the engine to the boat and then match the “proper size” prop based on “that” particular configuration! You can't just assume since someone else is using a certain prop, it will work for you as your configuration is different. When things are changed – it changes your prop requirements. If I was to buy a brand new boat, I would probably have the prop pitch reduced as I all ready know, I load my boats down with additional gear! I think it has been made fairly clear by now… If you are not at least at your minimum WOT rpm, you are lugging your engine down, which will result in excess wear on it. That is a proven fact and many experienced people on here are confirming that!

If you were to do a little homework, you would find the “correct” WOT along with your “MAX” WOT RPM. That is as easy as going on Mercury’s website. If you want to confirm it, drop an email to Yamaha tech support! I think this will answer some of your questions once and for all! Here are your specs:
http://www.piranha.com/Mercury.php

Motor Specs
Manufacturer: Yamaha
Year: 1992
Horsepower: 90.0
Cylinders: 3
Type: 2 stroke
Gear Ratio: 2.00:1
Min WOT RPM: 4500
Max WOT RPM: 5500
Spline Count: 15
Drive Type:

Not so sure, I would be propping it to 5800 RPM? You, might be getting your wish for a new outboard sooner than you plan, especially on an 18 year old motor! Now we know and don’t have to guess anymore? [:0]

If you were to also go on Mercury’s website and enter your information, you will find they have nine (9) different props recommended for your 1992 outboard! These props are based on the different types of configurations and they are: 14 x 11 x 3; 14 x 13 x 3; 13-3/4 x 15 x 3; 13 x 17 x 3 (semi-cleaver); 13-1/4 x 17 x 3; 13 x 19 x 3 (semi-cleaver); 13 x 19 x 3; 12-5/8 x 21 x 3 (semi-cleaver) 13 x 21 x 3. The complete Prop cost is: $139.25. If you buy the prop and it isn’t the right pitch – send the blades back and they will replace the blades, with a different pitch!

Now, while you are checking that tachometer (or having it done) as suggested, go on Mercury’s website and get an aluminum “13-3/4” diameter prop with a “15” pitch blades. If your true RPM (fully loaded) is reading 4900 the lower pitch should put you right in the 5300-5400 RPM range and will also take care of any future weight additions? You could also take off some pounds if you want to get the RPM back above 5000? But, hey… what do I know, I have only been doing this for around 50 years!

Have you stopped guessing yet? [8D][8D]

 

[profisher]

Charlie if it was your engine and like you say you carry heavy loads I would prop it to 5800. Just never take it up past 5500 and you will have less load on everything at cruise. Prop it to high revs but run it low = long life.

 

[Charlie]

quote:Originally posted by profisher

Charlie if it was your engine and like you say you carry heavy loads I would prop it to 5800. Just never take it up past 5500 and you will have less load on everything at cruise. Prop it to high revs but run it low = long life.

Can’t argue that point Rollie!
Like I said, a “lot” of good information thrown out there – he should be listening! But, as long as he is within manufactures’ guidelines, he is fine. Remember, there is a difference in experience levels and it is creating some confusion!

I personally, if it were my engine? Would fiddle around and have that thing pegging at 5500-5600 RPM, “fully loaded”! And, I think, we all know why?

 

[Sea Ranger]

Thanks Charlie!

And remember....Keep your tip up!!!

 

[Charlie]

quote:Originally posted by Sea Ranger

Thanks Charlie!

And remember....Keep your tip up!!!

Your welcome and – Here are some “last” thoughts for you!

First, you have figured out there is a difference when people are talking about "proping" a boat at WOT and the RPM you are running at cruise, right?

There is a difference between Yamaha, Mercury, and Honda operating ranges and 4400 verses 4900 RPM at WOT! And, a 2009 verses 1992 engine? I guess there is a meaning to different strokes for different folks? I don't think Honda even made a 90 hp until 1995, which was a 4 stroke with a maximum WOT of 6000 RPM? There are four 115 hp Johnson models made in 2000, with two having a maximum WOT of 6000 RPM and the other two 5500. But, I think this question has been concerning a 1992 Yamaha and insuring "it" is operating in the correct range? [:0]

Whoever the “two” mechanics are, who are telling you “In a nut shell” the engine is running fine at 4500 RPM” WOT – IS CORRECT! That is within "factory" specs! But, I would still get it closer to the 5500 RPM!

Whoever the mechanic is, who is telling you that a SS prop “is damaged easier” – appears to be WRONG! I don't know what he is thinking, if that statement was made? Sure you heard that right? SS props are nice (and expensive), but if you do hit something – as previously stated, the gears and shafts in your lower unit will usually be what gives first - before the SS prop, but not always! Personally, I run SS and happen to like regular old props better and find them easier and cheaper to repair and/or change. A prop is a lot easier than having to repair or replace a lower unit – which I have had to do!

Whoever is telling you that it is better to have your boat propped to the high-end of “max” WOT – is CORRECT! For reasons stated! However you decide to prop it just don’t run it over your “max” 5500 WOT! As everyone else is trying to explain you can prop your boat however you want and a prop will affect top-end MPH, but that really has nothing to do with being “properly” propped! Think of it like this, how far can you walk before wearing yourself out? Now - how far can you run, before wearing yourself out? When the engine is operating in its designed range (propped correctly at WOT)… it is walking! Anything else, either over or under - you are making it run. Just like you, it will wear out sooner! According to factory specifications, you need to be "propped" at a minimum of 4500 RPM and a maximum of 5500 at WOT for your engine to be "walking". Once you have it "propped correctly" where you want it, it doesn't make any difference what you are cruising and running it at 2000 or 5500 RPM - the engine will have less stress and is still "walking". That is the range which is “best” for the engine design! Note, the factory range doesn’t say anything about “skiing”, "hole shot", “MPH”, “weight", or "additional gear”! Your engine doesn’t know any of that and doesn’t care… the only thing it knows is how hard it is being worked and its best RPM! If you have a “full load” and at 4900 RPM you are fine - even though I would prefer closer to 5500! As you burn off fuel and drink that beer, you will notice an increase in RPM. You will also notice a decrease as you load the boat up with all those fish you are catching!

Think of it like this? You now have a pair of "work boots" on your boat and it is asking for "running shoes"!
Cheers

BTW... the last thought - I am not sure your dealer is a Jackass? Sounds to me he sold you a boat that is performing within "factory" specs?

 

[b.c. outboards]

this answer maybe days later but usually proper setup for a prop is to run the boat with a prop in close to what pitch you think is right based on experience and any good tech should have good idea from past setups on size and run the boat with just you and the gas and it trimmed up to its fasted speed and check the rpm then you have a better idea where you need to go with prop size based on w.o.t.

 

[Island Fish Lifter]

quote:Originally posted by b.c. outboards

this answer maybe days later but usually proper setup for a prop is to run the boat with a prop in close to what pitch you think is right based on experience and any good tech should have good idea from past setups on size and run the boat with just you and the gas and it trimmed up to its fasted speed and check the rpm then you have a better idea where you need to go with prop size based on w.o.t.

gee, ya think?

Fill the dam tub!