> When I stop it shoots a fireball out the exhaust! Mostly after a long run
> at high RPMs, like across a lake or field, doesnt happen with a quick blast,
> most of the time when the sled is under load or driving in deep powder for
> The backfire happens 1-2 seconds after I shut off the sled... What could it
> be? too rich on the mains causing a fuel buildup in the pipe??? I have a
> 330 main in now, stock was 350.
That is, usually, a result of turning the sled off, before you let it
idle down to a normal idle. WOT causes the pipe to get really hot,
then, when you turn it off, the engine keeps on turning for a while,
which pumps the normal gas, and air, mixture through the system, and
into the pipe, without burning it. If the pipe is hot enough, it can
ignite the mixture, and since it is close to the optimal air to gas
mix, it all burns at one time (just like it would in the cylinder, if
the spark plug had ignited it), hence, the "explosion". Most of the
time, this is an indication that you are running pretty close to
optimal, and it doesn't seem to hurt anything, but, it is always a
good idea to let the sled idle down to it's normal idle, before you
turn it off. That way, it cools the pipe a bit, and it doesn't pump as
much fuel mix into the pipe, since it stops turning in less time.
Hope this helps...
From the PC of Doug Bissett
doug.bissett at attglobal.net