Once in a while my tcat will backfire when I start it on a warm engine. Was thinking needle and seats. Any thoughts on this? What tip is better? Viton rubber tip or steel tip? Or could it be something else?
More than likely it is something else, it's caused by unburnt gas in the pipe(s) after shut down, caused by a high idle or sometimes it's unavoidable. Our old Wildcat efi was notorious for this and sometimes it would sound like a .357 magnum going off, ( no needle or seats in that thing)
Does it seem like your sled turns over a few times after you shut it off?
A lower idle helps in most cases.
Next possibility is an exhaust gasket or exhaust graphite doughnut leaking.
my F7 does this too once in a while. More so when its warm out or when im drag racing with my buddies. Try to let it idle down for 5 to 10 sec before shutting it down, this usually works for me. Hope this helps...
if its popping comes out the carbs its a lean problem if its pops out the exghaust its a rich problem. If its coming from the carbs I would clean the carbs make sure everything is okay in there and not plugged up the right jet sizes. If its coming out the exghaust its just fuel build up because your way too rich nothing to worry about its.