Ranger z21
Yamaha 250
Yamaha 25 pitch prop
Hydraulic Jackplate

Boat is LOADED DOWN and heavy

Back in May I started having trouble getting up on plane.
Brought my prop in, had it tweaked a bit, it didnt help.

Brought it back in last week, tweaked on it again and not much better.

Im running 4000rpm while getting on plane. Wide open Im running 5800rpm at about 64mph.

That seems right? Loaded down with fuel and two men Im at about 1200lbs with gear.

The prop guy told me its the hot weather/water. My motor kinda sounds like it may be "missing" when I trim it ALL the way down on plane, running about 40mph. Trim it up a hair and it sounds different. Never had a problem with motor, just had it PM'ed top to bottom and even check compression, all seems fine.

Question is, does anyone think the heat is being a factor? The density of the water (like hot air to an airplane) or the air heat?

I notice simular results last weekend, I quess it could be the heat?
I have never noticed it doing this until last weekend.

How long have you had it trimmed all the way down before trying to jump up on plane? If you drop off the pad, trim down, and immediately hit it again is it still sluggish or does it take off normally?

I have read some motors tend to load up when trimmed all the way down and idling for a long time like that and have to be cleared out (would explain your miss sound perhaps). I have never had a boat do it but I have had many a dirtbike do it when I would lose my mind and try a hare scramble race which involved a lot of low RPM negotiating of obstacles between full blast runs.

Just a thought, I'm not an outboard mechanic by any stretch, I stick to things with tires.

When it gets this hot your 250 drops about 10% in horsepower according to a factory rep that I asked. All of us that run big boats loaded run into the same issue with the heat. I run a 26 when its in the 80s or below and switch to a 25 once it gets hot. Makes the hole shot alot better and only give up a couple of mph but don't run it that fast anyway.
Kent

I have Ranger z522 with 250 mercury pro xs. Bought the boat last summer and had the same problem, took forever to get on plane. Fixed the problem by taking two of the three rubber orifice plugs out. they are located in front of the prop. I don't know if yamaha motors have the orifice plugs. Mercury said said with hot water the density changes. It fixed my problem for the summer. Winter came and had to put the orifice plus back in in order for the motor to perform properely.

After tons of research, I have come to the conclusion it has to be the hot air and water..

Can someone turn on the AC?

the hot weather is terrible for building hp in large carb an efi motors the combination of hot temps an summer blend fuels are not good things it you go to a smaller pich prop it will help or hope the weather cools off an your motor will run like it should the hpdis an optis are a little better but it effects them also.

i had my championship last year i could not get on plane either several boats had same problem they say when it gets hot its just harder to get on plane my father inlaw has a ranger he had same trouble but when its 40 it will jump out of the water

I have a 2001 Mercury Pro XB 250 and when you hit the trottle it comes up to 1500 rpm's and may stay there for 50 seconds or will not plane till I put someone up by the TM foot control. Sometimes it jumps right up. Run 92 or better fuel and the mercury 1,2 3 fuel system, check fuel pump pressure, replaced fuel line in the back to the motor, replace fuel filter, had the injector's pulsed checked. Run the motor on the third hole from the top on the transom. Had it in to three Mercury dealers with no luck. Anyone had this problem?

My 2001 Mercury 150EFI has been having same problem. Question: Am I hurting anything by running boat??? I use good fuel and the Stabilizer Treatment for ethanol.

ttt