hey all thanks for the input, im unsure of whats in it for a cam, but will certainly look into locking the distributor..........cheers

hey stevesxm, i posted the last reply at the same time as you .......was thinking the same thing about the cmi exhaust and adding mufflers but 2 late now as cmi's were sold. its just hard to believe that the silent choice affected it that badly, there has got to be alot of guys who have had to do the same swap with little or no issues.........i cant afford another "episode" like last yr-the boat flooded itself out in the middle of the st lawrence shipping channel and yes with a freighter hard on the airhorn for me to move the hell out of the way

I would agree with the theory of what you changed is probably the cause. I also agree that it is likely a reversion problem. Your cam may be to agressive to use silent choice.

just out of curiousity why would you think :

1) a cam that didn't revert before as a function of centerline and lift would suddenly do it now ?

2) why you would think that reversion would gas foul plugs ?

if the thing was sucking water back in i think you would see a whole raft of other and more serious symptoms ( and evidence) and if it was the cam then problem would not now just materialize after it had been fine all along.

when i repowered my boat a long time ago it had some sort of switchable system that dumped into a y pipe that existed under water ... i took them off and " threw them away " .

the guy that bought the one good 454 from me put it in a cruiser and couldn't do thru hull... so he used std manifolds and little exhausts and the y pipe. and he couldn't keep the plugs alive no matter what. so i convinced him to ( as a test run a old pair of gills i had with some cobbled up top exits.

boat ran perfect.

you motor is a big motor. when you restrict the exhaust like
( i am theorizing ) you have, what is happening is exactly what i would expect to happen.

you don't mention it but i assume that the boat runs fine when the exhausts are " open" . assuming that is the case, the only conclusion is that when they are " closed " they choke the ex enough to cause the issue.

nothing else makes any sense.

I am not an guru on the topic. Perhaps that is obvious. However, he said he added the silent choice and he has the problem when he idles. Seems to me with the water dumping into the exhaust stream before the silent choice and with the silent choice closed it would be more likely to revert than when it is open.

Reversion would not cause the plugs to foul. An increase in backpressure would. Chances are that he was right on the ragged edge of fouling the plugs before the switch and the increased backpressure pushed him over the edge. The 850 carb was on the large side to start with. An 800cfm is more than plenty and on the large side as well.

Without actually replacing the carb, I would do several things. Double check the float adjustments with the boat in the water. Next is start playing with the idle air bleed adjustment screws. Turn them 1/8 of a turn at a time for testing.

What is the idle rpm in neutral and in gear under load???
What spark plugs are you running???

hi all, yes the boat runs fine when the exhaust runs open...it even idle fines around the docks with it closed, this situation has happened a couple of times the last time i had to wait in line for fuel maybe 20 mins or so(idle speed only) fill up starts fine, leave docks get out to the open water...open exhaust get on the throttle to plane and no power, back fire up thru the carb and then dies on me. i did bring it to a qualified mechanic who replaced plugs,wires,distributor, etc he rejetted the carb because they were way to "fat" he told me his instincts tells him the motor mustve have had a supercharger on it and thus the "fat jets' he also did a comp check and all were around 150ish...............just trying to put as much info out there.........really appreciate all the feedback

check your fuel pressure,i run mine at 6 to 7 lbs psi,anything over 8 on a holley will not allow the needel&seat to fully close.at idle,the engine does not need much fuel,this is when the problem will be noticed the most.i also agree with locking the dist,a 9 to 1 compression engine will have no trouble starting with 34 deg of initial ig timing.i run my blower motors locked and they idel nice and clean,and i run farely large cams.i also agree with griff,unless your cam is grossly wrong,reversion wont foul plugs,the water in the cylinder just gets pushed past the rings.

Changing jets has ABSOLUTELY nothing to do with fouling plugs at idle. If a carb is too large, it needs bigger jets because of a weaker vacuum signal at the carb.

What spark plugs are you running and what is the idle rpm???
The float levels need to be set with the boat idling in the water.

what everyone else said!, my old 365 hp had a 800cfm Q-jet on it so i don't think a 450hp 454 with a 850 cfm Holley would be to big..Chit im running a 750 cfm on a 355 in my donzi and it loves's it..and what griff said the jets have nothing to do with the idle circuit in the carb..you also mentioned it back fired or popped,you may have blown your power valve's if you don't have the protection circuit in the base plate. do you have a 4 corner idle circuit carb? start out at 1/2 turn and dont go no more then 1 full turn out..turn the screws in a little at a time and wait for the smoke to clear and see if this helps..you may also have the wrong power valve in the carb,also if you turn the idle to high on the primary circuit on the carb your throttle blades are past the idle circuit and will load up..
ALWAYS set the idle with the secondary throttle blades or you will get a stumble off idle..