It likely backfired thru the mufflers cause yu keep letting it idle slow, when cold.
(this allows unburned fuel to enter the exhaust system)
2000+ rpm when you first fire it up. Keep the rpms WELL up until some heat gets into the blower. its not a taxi cab.
Blower motors need to "warm UP"
The simple dash mounted ignition power interupt toggle switch will allows easy cranking/starting when the engine is hot.
The vac sec carbs are not the best for the blower motor and will not save you gas
or do any of the other things you think they will.
Double pumpers work a lot better. Preferabily Holley 750 blower carbs with boost referenced power valves and 4 corner adjustable idle circuits, set up specificly for a roots blower.
+ down leg boosters and adjustable idle and hi speed air bleeds.
You will only getr so far with those carbs on it. They are not blower carbs.
Change the plugs, oil and filter before you go to the dyno session. Bring extra spark plugs and good fuel with you. bring holley carb gaskets, etc etc.
coat all carb gaskets wth vasoline or PAM cooking non stick spray so they don't stick and you can reuse them.
if/when you idle the engine in the garage, it is rebreathing its own exhaust gas and will load up and foul the sparkplugs. Blower motors need to be driven, not idled.
Last edited by F-BIRD'88; 11-11-2012 at 12:34 PM.