wHAT THE F@%$

[crownline79]

I LOST 10MPH ALL OF A SUDDEN WHEN THE ENGINE BACK FIRED AT FULL THROTTLE. AND EVERY 6 SECONDS OR SO A JOLT IS FELT THROUGH OUT THE BOAT. THERE IS ABOUT A HALF INCH OF GREASE UNDER THE U-JOINT, RIGHT ON THE TOP OF THE JET.
ANYBODY KNOW ANYTHING?
WONDER IF I JUST NEED TO LUBE UP THE JET, BUT WHAT WOULD THAT JOLTING BE?
HELP ME
PLEASE

[Havasuhog]

Sounds like you may have blown the power valve in the carb.
But what the hell do I know!:confused:

[cyclone]

sounds like an ignition problem. got more info on it?

[crownline79]

NO MORE INFO. BUT MAYBE US SITTING ON A SAND BAR FOR A WHILE MIGHT HAVE SOMTHING TO DO IF ITS A JET PROBLEM. BUT IF ITS AN IGNITION PROBLEM, WHAT WOULD IT BE?

[CrdStang]

I'm no expert, but I'd say that backfire tweeked something between the crankshaft and the impeller.
Might want to take a good look at the flywheel & bolts, driveshaft flange & bolts, while you have that stuff loose check the play on the pump shaft.
I had a car that'd shimmy once every 4-5 seconds at freeway speeds, turned out it was gross bellhousing misalignment. I only broke two pressure plates and a clutch disk before I figured it out..

[roostwear]

I'd pull the driveshaft, inspect the u-joints (probably wasted), put the hose to the engine and run it. Check the shaft alignment while you're down there.
When you say "jolt", is there an audible misfire, or do you "feel" it through the hull?

[crownline79]

feel the jolt throughout the hull.