kevin wrote:
Woodchuck wrote:


Running to lean?
What MAX RPM is the engine turning
Timing
Cooling system?
What is the engine temperature?


It could be running to lean, not sure but the carb is box stock but I did
set the idle mixture screws. He keeps it around 4000 rpm but it doesn't
overheat when he is going fast, just going slow. The timing I am not sure
about but I am going to get some timing tabs and run it at 8 degrees before
top dead center. the cooling system is very good, in my opinion. Its an
aluminum Griffin four core with an electric fan and no air in the system
that I could see and the radiator cap looks good as did the thermastat,
plus the fact that the engine just sits out in the open and he also bought
a small "radiator" that straps on to the oil filter. The motor will
definitely peg the 250 degree mark on the temp gauge but comes down once he
gets going at a good speed. I also noticed that the choke was not hooked
up and when I asked why he said cause it detonated. I am almost positive
it was just set up wrong with the timing. But have you ever heard of
coolant seperating? Having green coolant in the block but clear in the
reservoir? If I see it again I am going to see if its water from what he
is boating on.

We don't have air boats, however we do have plenty of hovercraft around
here, same idea.

The symptoms sound like detonation & as you allude the timing was
definitely suspect, if he just turned it till it ran best then it's
surely over advanced, add heat & detonation is in prospect.

The other less obvious thing is a lean mixture at high power causing
detonation. With some of the hovercraft, the engine is in proximity to
the fans low pressure side, if the carb is the normal top vented type
then the mixture can get leaned, a vent hose to a less effected (normal
atm press) area is the suggestion.

K