Yamaha 250 RPM's

[jkasperows]

Hey Guys,
my Gulfstream has a single 1992 Yamaha 2 stroke 250. what should my Max RPM's be? what should the cruse RPM's be? I have no idea what Prop size I have now but at WOT I am at 4,700 RPM. is this right? not looking for more speed just would like a good hole shot. and what would be good for fuel usage?


thanks

Joe

 

[catch22]

I had an 01 Yamaha 250 2 stroke on my 91 Gulfstream. I topped out around 5500 - 5600, (depending on load). Top speed was right near 40 mph, (light load). Cruise was around 4300 - 4500, speed around 24 to 27 mph, (again, depending on load). Unfortunately, I do not remember what size prop I had.
Even though the owners manual states that the wot range is 4700 - 5500, imo, 4700 is way too low.

 

[choogenboom]

I had 1994 250 Yamaha on a 228G, and when trimmed just right it would run at 5600-5700 RPM. Prop was marked, if memory serves, with "17M" which I think means 17 " pitch and I think it was 15 1/4 diameter. I did not have a fuel meter so can't tell you what to expect there.

4,700 RPM is definitely too low. How long have you owned the boat and was it always that way? What is your prop pitch and diameter?

 

[jkasperows]

250

i have owned the boat for only a month. I will pull the boat out of storage this weekend and see if I can find any numbers on the prop. I have trim tabs and have run them up to down but cant get much more RPM's. the bottom is waxed and no paint. It looks like I should be running a 17 pitch prop. engine runs great so will have to check the prop. thanks for the help

Joe

 

[choogenboom]

Good luck! There are many other possible reasons for low RPMs so if the "prop to big" angle does not pan out let us know and we can continue to narrow down the possible causes.

 

[JUST-IN-TIME]

my book is at home
i want to say around 5500

 

[NIGHTIDES]

17M is the prop you would want to run.

Equally important, what hole is the engine mounted in..??

Mine was mounted too low w/ the cavitation plate underwater. Pulled the motor and mounted it in the top hole and the RPM's came up to spec which is 5500RPM for that engine.

 

[jkasperows]

OK,
finally got down to the boat to check the prop and it is a stainless steel prop that has a 17-M on it. now what? engine runs and sounds great just not getting the RPM that I think I should at WOT.

 

[NIGHTIDES]

17M is the prop you would want to run.

Equally important, what hole is the engine mounted in..??

quote]

You need to answer this . It will go a long way to knowing what problem if any you may have.

 

[catch22]

Are you trimming up the motor somewhat? Makes a big difference. In calm conditions, with no tabs, (fully retracted) trim the engine up. If it starts to cavitate, or if the boat starts to "porpose" back it down a little.

Are you certain the throttle is advanced as far as it will go? You can check this by disconnectiing the throtlle linkage at the motor. Advance the engines throttle as far possible. Now advance the throttle lever and see if the cable itself is extended far enough to match the motors linkage. Check for any restriction. Also, this might sound stupid, but... the throttle lever itself can be moved, or repositioned. On one of my boats, the lever was "set back", off center, by one notch, I think purely for comfort. If, for some reason, yours is set "forward" - off center, that might prevent it from reaching full throttle.

I also agree with what Nightides is saying. Check your transom height. With the boat out of the water, lower the outboard untill it is vertically straight, (anti-cavitation plate should be parralel with the bottom running surface of the hull). With a bracketed outboard, the anti-cavitation plate should be a couple of inch's above the keel, (center). If the plate is even or especially below the keel, move it up.

 

[JUST-IN-TIME]

5500 rpm is max rpm
shoot for 5250, it will last longer

 

[jkasperows]

250 RPM's

Thanks Guys!
I will try all of the above. I will post what I find out.

Joe

 

[gw204]

Every bracketed Grady I have seen (assuming your's is bracketed) has the motors mounted too low. General rule of thumb is to mount the engines so the anti-ventiliation plates are 1" above the hull bottom for every 12" of setback the bracket provides. My engines were intially mounted in the bottom hole which put the plates about even with the hull bottom despite being around 30" back. I had them raised two notches which picked them up about 1.5" and that proved to be just about perfect. Any higher and I think I would have been losing bite in a following sea.

Only after you get the engine height correct, should you start looking at changing the prop.

 

[jkasperows]

250 RPM's

Thanks Brian,
Yes I'm on a bracket. by your description, my motor is mounted way too low. Now to get this corrected. I would have never figured this out without everybody's help

thanks again

Joe

 

[choogenboom]

Wish I had checked on my 228 as at the time I sold it the engine was set on the lowest hole. In case anyone wants to see what something looks like on a 1994 Grady 228G, I took lots (94) of close up and detailed pictures of mine and posted them here when I was selling the boat. Clearly shows the engine on the 1st hole.

http://gradywhite.shutterfly.com/

Chris