There's so many posts on WOT RPM's, but what if....

[kshelly]

OK, I've read a gazillion posts concerning WOT RPM's. I understand the importance of not reaching or going past the recommended RPM at WOT. But what if the engine is rarely operated at WOT? What if 1/2 or 3/4 throttle is sufficient for what you want the boat to do? Is it recommended to "open her up" every now and then? Just curious.

 

[jim dozier]

Re: There's so many posts on WOT RPM's, but what if....

In the discussions about props and WOT it is important to select a prop that will let the engine reach maximum recommended rpm at WOT. Then you will know that the prop is not overloading the engine. It does not hurt the engine to run it at, say 4000 rpm, if the prop selection will allow it to reach 5500 rpm at WOT. It is, however hard on the engine to run it at 4000 rpm if that is WOT on an overpropped engine. In the latter case you would be lugging the engine. That said it wouldn't hurt to open it up once in awhile and blow your cobwebs out. Oh and it will probably help the engine too .<br /><br />Sometimes it is easier to grasp the picture if you exaggerate the situation to the extreme. Suppose you changed the prop on a properly operating engine that would reach 5500 rpm at WOT to a BIG MONSTER that would only let it reach 900 rpm at WOT. I think you can see that running the engine at WOT and only reaching 900 rpm would overheat the engine and cause a host of problems (not the least of which would be getting it not to stall when you put it in gear).

 

[LubeDude]

Re: There's so many posts on WOT RPM's, but what if....

Originally posted by erau85:<br /> Is it recommended to "open her up" every now and then? Just curious.

The cleanest engines the outboard mecanics see are the ones that are run hard. If you are running easy all the time, you must decarb at least once a year.

 

[roscoe]

Re: There's so many posts on WOT RPM's, but what if....

You still need to set up the engine/prop, to achieve the recommended wot rpm. With this set up, there is the correct amount (not too much or too little) of stress on the internal parts of the engine.

 

[Glenmac]

Re: There's so many posts on WOT RPM's, but what if....

Jimd<br /><br />Thanks for that explaination, I have been reading alot of these posts trying to learn and that really helped me to understand the propping of my boat better.<br /><br />Glen

 

[Stumpknocker]

Re: There's so many posts on WOT RPM's, but what if....

Lubedude.... I almost never open up my 48 SPL. I baby it constantly as did the previous owner. Yet I have never had to decarb. 2 years now. Tops of the pistons and heads are clean as a whistle. "Lucy! You got some splainin to do." What am I doing wrong that I don't get to decarb like everyone else? Not!

 

[walleyehed]

Re: There's so many posts on WOT RPM's, but what if....

The extremely expensive result of build-up is under the piston rings in the ring lands that you can't see. That is why alot of times we decarb and double-check compression, and it's not uncommon to see a noticable increase.

 

[jafa]

Re: There's so many posts on WOT RPM's, but what if....

I'm gonna do my little suzuki dt40 tomrrow with a can of merc powertune, Cant get sea foam down here. I'm ok about useing the can in the carb till it dies and then into each cylinder thru the plughole , question is how do you "force it" into the ring lands at the top of the cylinder , tilt the motor all the way back and bring up each cylinder in turn manually ?

 

[walleyehed]

Re: There's so many posts on WOT RPM's, but what if....

as you spray it into the engine while running until it quits, it allows plenty of it to get behind the rings.