1991 4.3 L Mercrusier V6 top end power issues

Worthaug

Recruit
Joined
Jul 26, 2016
Messages
2
Thank you for welcoming me to this forum. I recently purchased my first boat. It is a 1991 Chaparral 1900 with an inboard Mercrusier 4.3L V6. I have worked out all the corrosion issues and fuel issues and it starts and idles great. However, there is no top end power. Alone in the boat, it tops other at 3200 rpms and won't plane out very well (large wake). When loaded it won't get past 2600 rpms. I've narrowed it down to a fuel delivery problem, either the carb or the pump. I cleaned the carb screen filter and bought a ln online fuel filter but haven't installed it yet. What are your thoughts. Thanks in advance.
 

philbullet

Petty Officer 1st Class
Joined
Aug 14, 2014
Messages
241
I'd check your fuel in tank, start at tank and check hoses, fuel pump presure , etc.
You may want to do a compression check just to make sure
I just had trouble with water in gas tank and low fuel pump preasure. Fixed those isues and it was 2 of the 5 problem s I had.lol
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Thank you for welcoming me to this forum. I recently purchased my first boat. It is a 1991 Chaparral 1900 with an inboard Mercrusier 4.3L V6. I have worked out all the corrosion issues and fuel issues and it starts and idles great. However, there is no top end power. Alone in the boat, it tops other at 3200 rpms and won't plane out very well (large wake). When loaded it won't get past 2600 rpms. I've narrowed it down to a fuel delivery problem, either the carb or the pump. I cleaned the carb screen filter and bought a ln online fuel filter but haven't installed it yet. What are your thoughts. Thanks in advance.

Howdy

Agree it could be a weak motor and a compression test will provide that insight. If compression is OK, my first thought is you have the wrong prop on the boat. My second guess is the drive was replaced with the wrong ratio.

What prop pitch is on the boat?
 

wahlejim

Master Chief Petty Officer
Joined
Jul 23, 2015
Messages
884
Before you put any money in the boat, get it weighed. Worst case scenario is that it is water logged and bogging you down. Eliminate the worst case and go from there. Nothing worse than throwing money at a problem only to find out there is nothing you can do.
 

wahlejim

Master Chief Petty Officer
Joined
Jul 23, 2015
Messages
884
Your dry weight should be in the 2200 range, plus weight of fuel and trailer. Go from there.
 

Worthaug

Recruit
Joined
Jul 26, 2016
Messages
2
The prop is stock and compression seems good. When set to throttle only the motor sounds perfect but under load it struggles. It was 2340 with trailer on the scale. Not sure if the drive was replaced or not.
 
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