Max rpms are only 4200 when wide open. 2001,115 yamaha

[Jason2tpa]

Your engine has a 4.25" gear case. The most common prop diameter for this size gear case is either 13" or 13.25". The number 20 you see followed by the "x" indicates the pitch (D x P).

The spec rpm range @ WOT for your engine is 4500-5500. So indeed you are experiencing low rpms. Action craft hulls are fairly lightweight considering the length. Assuming your engine is not the reason for the low rpms, if you drop down in pitch you will see an increase in rpms. You need at least an increase of 1000 rpms, but preferably you want to reach top end of rpm spec at 5500.

Deciding what prop and pitch so your engine performs at top end is not an exact science. Trial and error, really. But knowing you need at least 1000 rpms, a rule of thumb to use that estimates rpms with change in pitch is 150-200 rpms for every inch. So if you're going to trial props, start with either a 15", 16", or 17" pitch.

[dray0151]

2000 C115 TLRY.

2000 C115TLRY Yamaha Outboard Parts

Should be your engine.

[dray0151]

The attached link gives you several options that would be from Yamaha as far as props and pitch. I believe these listed are all three blade

2000 C115TLRY Yamaha Outboard LOWER CASING DRIVE 2 Diagram and Parts

you can google many other prop manufactures such as Solas etc.

[99yam40]

I'm told it used to run at 5200 rpm 10 years ago

If it was with that same prop, you have motor problems now or something bad his going on with the hull or set up

[TownsendsFJR1300]

Yes ivery had it for about a year. And sorry it's a 2000 115tlry 2 stroke

Ok, have you ever seen it run to 5500 or run the engine recently or ever (prior to working on it now)?

We need a little back-round (maybe a-lot) on the rig.

Did the engine sit for a year with old fuel, has the tank been pumped out of old fuel, etc?

Agreed with 99. Before you start re-propping (if even needed) it needs to be determined if there's an issue with the engine...

[Mr.nitrox]

First off tank you all very much for the help!

I've never seen it go past 4200.. before I did the recent maintenance it would stall out if I ran above 3500 rpms for long, but after replacing the fuel pump and cleaning and replacing some parts on the carburetor, that problem went away..

The boat did sit for several years before I got it a little over a year ago and got it running again. I flushed out the fuel lines and drained the tank when i got it. but nothing other than nonE has been run through it, so I'm told, and thats all i use. But judging from how clean the carb was i belive it.

[Mr.nitrox]

I also recently inspected the hull below the water line preetty well while snorkeling and it looked good, no dammage or abnormalities.

[Jason2tpa]

You can use the yamaha or mercury prop selector website as a helpful tool if you decide to change props:

Yamaha.net

https://www.mercurymarine.com/en/us/...tor/#/step-one

[TownsendsFJR1300]

Ok, good. Since draining the tank, did you clean out the fuel pump for any debris that may have been in there? It may have been pumped into your clean carbs (now with fresh crap in them).

You can drain the carbs with the drain screws AND CATCH what comes out. Prime the primer bulb some to flush as well. (I use a small CLEAN tuna fish can that fits in tight spots to catch fuel).

You said you DID pull (not just spray) all the jets, especially the main jet?
Could you see light thru the jet fully when it was out? If not, "do over".


Looking at the carb parts diagram:
http://www.boats.net/parts/search/Ya...TOR/parts.html
your main jets are directly UNDER the float drain bolts. (real easy access)

Pull the bolts and drain the carbs. Then pull and re-check the main jets. Most mains are slightly higher up in the carb body.

Yours are as low as they can be and likely to clog up if there's any crap in there...


**Also not mentioned, did you do a compression test on the engine, just to ascertain it's mechanical health?




.

[Captn Dave]

Have you replaced the fuel filters?

I tried a couple of the prop calculators and with the numbers I punched in, it seems your engine should reach the RPM even if the pitch was 26"

[pstephens46]

Wonder if there is a test wheel available for this motor? I was told on another forum that Ken at propgods has a few to lend. He would prefer you to buy from him as well.

I wouldn't spend a dime on props before determining health of motor.

Does this boat stay in the water all the time?

[JerEazy1]

Not sure what the debate is about - he's over propped - or at least that is where to start. If the Engine freely revs up to the 4200 and doesn't stumble or studder on the way, then it's not an engine problem.

If he's got a 20 pitch prop (11 x 20, 14 x 20 or any variation of that) he's way over for any 115 hp engine I've seen or used on an 18 ft boat.

Generally 200 RPMs per pitch increase or reduction. Go get a prop that fits (e-bay, or from a member here, craigslist or wherever. Get a cheap aluminum as you don't need a stainless with that HP range) and go from the 20 pitch to a 17 pitch 3 blade and that should get you to 4900 -5k (losing a blade gives you 100 rpms back generally). (https://www.amazon.com/Michigan-Whee...1%2C6033932011)

I would HIGHLY recommend a 15 or 16 pitch 4 blade if you want to keep the 4 blade and you need the stern lift. That'll get you to about 5200 which is a nice sweet spot. (https://www.amazon.com/AMRM-941415-2...1%2C6033932011)

There are other factors involved (weight on the boat etc) and for all you know the previous owner got 5200 rpms 10 years ago before he changed the prop.

Swap the prop and report back.

[99yam40]

I did not see where the OP said he replaced the prop, so we need him to tell us if the one he has on it now was the one that was able to run 5200 years ago

[JerEazy1]

I'm told it used to run at 5200 rpm 10 years ago

Yes ivery had it for about a year. And sorry it's a 2000 115tlry 2 stroke

He's had it for a year and hasn't changed the prop - not much of a stretch to assume the prop was changed at some point between when it ran 5200 rpms 10 years ago and the year the OP has owned it. We've all run into that guy who thought "more pitch, faster boat!" or bent their prop on something and bought whatever the guy at west marine said to buy.

Instead of tearing into the engine - prop it down and see if that solves the problem. It is the easiest, quickest, and most logical solution.

Not being on load doesn't prove much of anything besides the fact that the engine can rev past 4200, but drop it in the water (not on the hose) and see if it'll rev past 4200 without the prop engaged. If it does, switch the prop.

[TownsendsFJR1300]

NEVER ASSUME anything...

He's had it for a year and just starting to work on it.

He was LAST told it turned 5,500 PRIOR to him obtaining it. NOTHING MENTIONED about in-between owners.

And there was no mention of simply going to WOT out of the water on muffs to obtain 4,400 RPM's.

Most folks know it must be on the water, loaded, etc to get an accurate WOT #.

The OP is apparently aware of it as he's mentioned 5,500 but only gets to 4400..

+1 with Yam99's last post, re same prop, same 5,500RPM's?

Hopefully it IS a simple prop change.