superjet Power fades when warms up

[winterstick]

gday
I have a 97 superjet here the ski run super when you first go out but after about 10 minutes the power sort of fades away, like its running out of fuel but still runs smooth but lacks a lot of power.
out of the water bypasses we have small black deposits on the hull like black dandruff
it has
billet head (orings ok)
82mm pistons (comp is good)
Brand new stator (genuine)
brand new coil (wsm)
46mm carbs (tried lots of jetting variances still no change)
any ideas please

 

[WAB]

Do you have the overheat sensor on the aftermarket head?
Trim back plug wires?
Check compression on hot motor?

 

[Mouthfulloflake]

an exhaust leak? hood could be filling with exhuast, and makes the engine struggle fo fresh air.

have you blocked off the hood holes?


fuel filters clear, the ones in the line, AND the ones on the carbs?
fuel hoses soft? pinching?
a kinked line?

pulse line soft? maybe gets hot and pinches?

I could see heat aggrevating a stator winding problem too.

Lots of variables here, narrow it down some.

try running on reserve, does that change anything?

 

[SUPERJET-113]

Check fuel filter and basket filters in carbs? and yes a heat soaked stator can do that too.
The way you talk about the black stuff, maybe their is something clogging the cooling passages or lines a bit and its overheating and the sensor is kicking in?(Like WAB mentioned to check).

 

[Mouthfulloflake]

could a head gasket, or exh gasket breach put that black stuff out the pisser?

maybe its getting some water into the combustion chamber?

it would run like that !

\I had one that was leaking and wouldnt get many RPMS when it was leaking.

pull a plug and see if they are milky

 

[winterstick]

A bit more info
type 9 pipe (pressure tested ok)
thanks for the ideas
it doesn't have a heat sensor
new coil like 10 minutes use
no exhaust leak (runs the same with hood off)
tried it with new fuel filter and no filter
PULSE LINE is a clear tube which I will change after i fix whats in the pictures
stator is brand new
carbs are rebuilt and checked before last ride filters new too
now the pics, I pulled off the head and found these marks on the pistons, looks and is the pistons hitting the head, not hard but it is hitting, the head is an o-ring style but I know a gasket would raise it enough to clear

 

[shepster]

Pretty sure you cant use a gasket on a head that is designed for o-rings. You will have to get some relief cut into your domes to fix the problem.

 

[standupjetski_com]

Had the same problem. I could blow through both aftermarket filters with no prob, but they were bad.
Try running fuel line directly from reserve to carb inlet

 

[keefer]

You need to check the squish relief and make sure it is not way too small. What cranking compression are you running? Are you running a standard base gasket? Looks like you have some major clearance issues going on there.