Boat MPH

[bassmike]

Recently bought a boat and took it out a few times and top speed was about 53. It has a pro v yamaha 150. Was pre fishing for a tournament and all was well. Next day took it out and exact same conditions and only ran 45 top speed. Can any one tell me wats going on I use 86 octane should i be using higher or what? Im confused.

[FISH2WIN55]

Are you going off the speedometer in the boat or GPS? If you are going off the speedometer in your boat than it may be that it is off. In all the boats I have had the speedometers have all been screwy. If it is GPS than I would say it is something else. Or are you talking RPM's.

[Phil]

SOMETIMES, ITS ALL ABOUT THE WEATHER ???

[bassmike]

Off the Gps. It does have a jackplate as well maybe it could have to do with that?

[crawdaddy]

Was the boat trimmed out? My boat will only do about 48mph when the engine is trimmed down at full throttle. It will do around 70mh at full throttle when properly trimmed and up on pad. Did the engine sound like it was running strong and not missing or anything like that? Was the second reading at different altitude? Was your GPS functioning properly?

[Smile_n_Jax]

Yes, it very well could. How the motor is trimmed has a big impact on speed and you'll probably have to experiment. I bring mine up on pad at about 4000 rpm and start trimming up watching the tach. When the rpm maxes out, that's the sweet spot. I then take the rpm up to where I want to run. At that point I may have to fine tune the trim.

Don't know about your motor, but for mine Yamaha says to NOT use higher octane gas.

[bassmike]

ya all was good and i tried it at the same lake, the engine sounded great and runs good, i just dont know what the problem can be the gps reading is fine too. the engine was trimmed up

[bassmike]

when the boat is at 45mph its running about 4000 rpm's

[DeltaDan]

ya all was good and i tried it at the same lake,

Were they draining that lake ??


As much clean water as they are sucking out of the Delta daily -- It has been known to happen up here as well .....

[blackcloud]

Mike,

If you are only getting 4000 RPM out of your motor at full trim (PROVIDED THE TACH IS SET PROPERLY) you are too deep. That is, the jack plate needs to come up. A Yamaha should turn more than 5000 RPM if set and running properly. I don't own one as I have always been a Merc guy but I know several that do and Have driven them. My Dad's 175 turns 5250 at top speed and runs about 62-64 MPH on a Skeeter. I would say thatv you need to raise your jack plate.

What size prop do you have?
How far above the deepest part of the hull is the prop shaft?
is it a 10" jack plate or an 8"?

Bottom line is, you need to find out why you cant get the RPM

S-

[brambo0311]

Just a guess but did your jack plate slip down? Check for old wear marks. Might not even be possible with your jack plate.

[Smile_n_Jax]

If you're only getting 4000 rpm something is drastically wrong. Either in the motor or the set-up. My 90HP is rated to 5600, though I never spin it that high. Since the boat is new to you, maybe you should take it to a shop and have everything checked out.

[Old School]

Mike,

I have a 95 Skeeter with a 150 Yamaha Pro V and have had it up to 63 MPH with trim up 4/5 on gauge. Don't know the RPM though because I'm trying to watch where I'm going!

[gabuelhaj]

If all you're getting is 4000 RPM's, then something is wrong. You are missing 1500 RPM's!! Don't think a slipped JP will cause this. You need to get it checked before you lean it too much and then kaboom!

First, verify your linkage and make sure your butterflies open up all the way at WOT, then do a compression test if that checks out.

You should change those fuel pumps with gasket's every 3 years. Replace your primer bulb, fuel filters, inspect your plugs, do your spark test, may have a bad coil(s).

You can post your problem at www.yamahaoutboardparts.com and they'll help you too.

Good luck!

Glenn