1989 Mercruiser Bravo One 457 Magnum power loss

[Jerry Baja]

Problem has developed in the last week. Motor starts easy, idles smooth and runs smooth at different speeds. At 3000 rpm it will run well, at 4000 rpm it will run smooth there as well. There is no loss of power bring the boat up to plane and no hesitation. But if I try to increase the speed quickly the engine will drop off and lose power boat drops off plane I pull the throttle back and the motor is still running at idle with no miss. i can put it back on plane immediately with no ill affect in power. The boat weighs 4000 lbs. The tach is not working as designed it fluctuates at times and does not read accurately at 600 to 1500 rpm. I do know that at 3000 rpm there boat does 30 mph and it is doing that so at that speed the tach is correct from past performance. I also know there is at least 3 floats loose in the gas tank. I have changed the fuel filter. Any help would be appreciated. thanks

 

[alldodge]

Howdy

So your saying if you throttle up quick it bogs down, but if you throttle up real slow it does OK?

If this is the case then you need to fix the accelerator pump in the carb. The accelerator pump pushes extra gas in the crab during acceleration

Edit: changed down to up

 

[Bondo]

Ayuh,.... Welcome Aboard,.... I agree, it sounds like a Carb problem, accelerator pump in particular,...

 

[Jerry Baja]

Thanks for the suggestion but If it is the accelerator pump why doesn't it lose power from a dead stop or idle speed when i accelerate hard to get the boat on plane? The boat accelerates quick without hesitation to plane out plane out speed 22-25 mph. thanks again.

 

[Bondo]

Ok,.... Maybe a fuel restriction, starvin' the acc. pump when at speed,...

Maybe the bowl is 'bout empty at that many rpms,....

Have ya examined the Contents of the fuel filter for anything but clean fresh gasoline,..??

 

[alldodge]

Thanks for the suggestion but If it is the accelerator pump why doesn't it lose power from a dead stop or idle speed when i accelerate hard to get the boat on plane? The boat accelerates quick without hesitation to plane out plane out speed 22-25 mph. thanks again.

Basically because I'm not understanding what your saying, this is why I post my thoughts, (edited down to up in above statement). In your first post it sounded like if you throttled up slow it would do fine, but if you did it quick it would bog.

This comment is confusing to me

But if I try to increase the speed quickly the engine will drop off and lose power boat drops off plane I pull the throttle back and the motor is still running at idle with no miss. i can put it back on plane immediately with no ill affect in power.

So if you can acceleratee from a standing still with no issues and only later have problems once on plane then you have a restriction or a weak fuel pump. Check what Bondo mentioned