mercruiser 4.3 Slow acceleration at WOT

[Sunesta]

Here’s what’s happening: second season I’ve had this Chapparal Sunesta 210. Last season I put a new carburetor on. It ran good while give it throttle but had trouble starting and idling. This season I had the carb serviced by company and now starts and idles great. (I also replaced the fuel pump, and everything related to spark.). BUT, the boat takes much longer getting on plane and will only get to 34mph at WOT running at 4000-4500 rpm. I’ve opened up the carb to verify nothing is stuck or really out of spec…all seems fine. Same prop as I’ve always had. Could try changing it I guess. Thoughts anyone?

 

[Lou C]

If you have a 21' boat with a 4.3 its not going to have a high top speed, mine is at most 40 mph. Your max wide open throttle rpm should be at least 4600, you can go as high as 4800 for better acceleration.
What carb, is it a 4bbl, are the secondaries opening up as they should?

 

[markhodges78]

Here’s what’s happening: second season I’ve had this Chapparal Sunesta 210. Last season I put a new carburetor on. It ran good while give it throttle but had trouble starting and idling. This season I had the carb serviced by company and now starts and idles great. (I also replaced the fuel pump, and everything related to spark.). BUT, the boat takes much longer getting on plane and will only get to 34mph at WOT running at 4000-4500 rpm. I’ve opened up the carb to verify nothing is stuck or really out of spec…all seems fine. Same prop as I’ve always had. Could try changing it I guess. Thoughts anyone?

What was your speeds before having the carburetor worked on? Your WOT rpm of 4500is close to where it should be so if your getting he correct WOT rpm then the problem isn't in the carburetor the only way to get more speed is getting more boat movement from the rpm mabe prop slip or the boat just digging into the water more than usual just my guess

 

[poconojoe]

I'm no expert, but a 21 foot boat seems like borderline size for a 4.3.

A 4.3 is not much of a screamer. Mine kind of rolls up to speed.

My 18 foot maxes out at around 45-48 mph with a 4.3. It does get up on plane within seconds though.

How old is the boat? Could any of the floatation or structure be waterlogged?

Are you trimming the drive all the way in/down when attempting to plane? When you trim it down, does it actually trim all the way down or is something preventing it from doing so?

How many passengers?

How's the weight distribution? Anything heavy up front? Anchors, batteries, etc.

You may be able to get a bit more rpm's out of it with a propeller change, but your readings are already pretty close to maximum.

I still think that's a lot of boat for a V6.

Hope you find a solution.