bogging 4.3 under load

2003 sea ray 4.3 mercruiser ,it all started when i blew out a trac in my headgasket from my cylinder to the pushrod hole and melted the plastic baffel in my valvecover.i replaced the headgasket,and valvecover.but it didnt run right after that.it boggs under load in the lake,barely making 1200 rpm,but works good with the muffs on in the driveway.so first thing i found was some oil in the top of my coil,so i replaced it thinking this was breaking down under load,didnt work,then i got rid of the electronic ignition because the spark wasnt being advanced,found a mallory dual point ignition to try, didnt work.then i replaced the carb with a 450 cfm holley,didnt work,rechecked firing orders,replaced wires,fuel filters,checked fuel pressure,im really loosing face here,my wife is at witts end with me,and i could really use some help,is there anything in the leg that would rob power or in the exaust manifolds that would do this??

Rule out the obvious...vacuum leak, fuel starvation, wonky throttle linkage, low battery, bad electrical connections, bad gas.

o2batsea said:

Rule out the obvious...vacuum leak, fuel starvation, wonky throttle linkage, low battery, bad electrical connections, bad gas.

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have done all that, i have been fooling around with this for two seasonsjust wondering if there is something in the exaust manifolds that can block the flow or can there be something in the leg that can affect the power in the waster keep in mind it works good with the muffs on and as soon as u drop it in the lake it boggs

Been debugging and fixing things for a very, very long time. That said... While two simultaneous unrelated failures are not unknown, they are rare, therefore all of the stuff you replaced that wasn't related to your original failure was a waste of time and money. I would look close to the point of the presenting failure, i.e. the push rod hole, possibly a damaged lifter in that hole or some melted plastic. If it was damaged, there is a fair chance that the related valve did not close all the way. If that happened, you are probably looking at a burned valve. Have you done a compression check on the engine?

You need to post this question on Boat Owners United on Facebook!! http://www.facebook.com/groups/boatownersunited

There's over 32,000 members, and you would get multiple answers on this literally within seconds.

sandkicker said:

Been debugging and fixing things for a very, very long time. That said... While two simultaneous unrelated failures are not unknown, they are rare, therefore all of the stuff you replaced that wasn't related to your original failure was a waste of time and money. I would look close to the point of the presenting failure, i.e. the push rod hole, possibly a damaged lifter in that hole or some melted plastic. If it was damaged, there is a fair chance that the related valve did not close all the way. If that happened, you are probably looking at a burned valve. Have you done a compression check on the engine?

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yes the compression test was good 120psi across the board, the engine works great including the accelleration with the muffs on even kicked it into gear with the muffs on and it worked grreat, but its when u drop it into the water and through it into into gear then it boggs on accelleration,kick it into neutral and it revvs up normally

Engine performance on muffs is of minimal value... In gear in the water is when the engine actually "works'.

In exhaust path issues... did you check the flappers? Which Merc drive?