I have a 98 Nitro 800 with a 150xr6 with 828 hours. The last two times out in the afternoon when I go to take off it starts to rev but then it just falls on it’s face on take off. Most of the time the engine stays running. I would try bringing up the rpm’s before nailing it and after 3 or 4 tries it will take off and run normally. Now keep in mind it doesn’t do this in the morning. It will blast out of the hole no problem in the morning. I suspect a stator. I went through the carbs last winter. New spark plugs this season. All of the ignition is original. Would appreciate your feedback and experience on this issue. Thanks. Another thing that might be related to the same problem is when I try to use the motor to put the bow against the roller it won’t rev like it used to and just die. I have to use the winch to pull it up.

Rick Welcome iam not a boat mech, But i would start with simple things. 1 Change fuel filter/s , How old is your gas in boat ?? It almost sounds like prop hub is going south, Strange it doesn't do it in morning/ cooler temps. I know carbs can be a pain!!!. Possible the float level is a little low. Definitly make sure fuel is fresh, even if you have to drain. When i went to look at a P2 with merc 200 efi. It would not run, fired up, die immediately, i checked copression/ good. Cylinders were getting spark. So motor need 2 things to run. So i took a gamble bought it for less than 3k. Took to a mech. He put new fuel filter [2] plugs, Impeller. Few days later sends a video of it idling & peeing a strteam. Thats been 9 yrs ago. Talk with fellow boat owners and get a good mechanic. Best of luck.

check everything fuel related.. inline filter, hoses, bulb, pulse pump.. when it starts tha downside at launch check bulb for being collapsed/soft.. if so pump it while its actin' up.... if it improves replace bulb.. still does it, rebuild pulse pump.... jmo

I have an XR6 as well that occasionally does this too. Always when it is hot out. You have to prime the bulb on every start where the motor has been sitting over a half hour or so. The gas evaps from the motor when it's hot and since it is carbed and not fuel injected, the motor needs fuel, hence hitting the bulb firm and idling it a bit before you try to get on pad.

Heard this from 2 different Merc guys on BBC boards. Common with that engine. Never happens in the winter.

Thanks for all the good feedback. I will let you know what takes care of this issue.

Please do if you find out what is doing it and you solve it. I live with mine doing it and it is frustrating at times for sure. Good luck

a small, low pressure electric pump and relay puts all those bs problems ta bed..................... hot, cold and everywhere in between

It won't explain your morning versus afternoon issues but next time you have the carbs apart check your floats for pinholes. All it takes is one small hole in one float to cause problems. My 175 Black Max did exactly what 4weight described. After running hard and then stopping for a while it was hard to start. It was definitely carburetor issues but don't recall exactly what. One time my mechanic got some faulty needles. It frustrated the carp out of him. I took him to a lake to diagnose it. That time I called the dude that runs the Mefcury school in Richardson. He said that Black Max's are temperamental about float settings. My mechanic somewhat disagreed but the 2 had some history. Another time I had fuel lines going bad. If you have not replaced all fuel lines with ethanol resistant. I think after owning the Black Max for 35 years I could do a carburetor rebuild in my sleep.

put one on my 87 xr2 150, then eliminated the "idle stabilizer box" , ran it for 20 years all was good