Your need for a sniffle valve may have something to do with your setup. I had a sniffle valve configured on my IO-360-M1B (Superior) with EI and a light weight Whirlwind prop and had two kickbacks, the second one that damaged the starter ring gear and required repair. My sniffle valve was plumbed at the end of about 18? of hard line coming from the forward tap in the forward most location on the intake manifold and sitting back near the exhaust area of the cowl on my RV8. When I discussed the kickback situation with my engine guru, Jimmy (JB Aircraft Engines), he recommended that I install the sniffle valve on the case, where it belongs, and that I install it in the aft most tap on the manifold, especially since it?s a taildragger. It seems that a slug of fuel still residing in the aft portion of the tilted (taildragger) manifold, including the 18? of hard line upstream of the original valve placement, might be enough residual fuel to trigger a POP in the opposite cylinder in a lost spark EI setup. Well, I changed things according to Jimmy?s recommendations and I never experienced another kickback. I don?t know what, if anything, these changes had to do with the results, but I was happy that something worked. Never experienced another problem.
If you have a heavy prop and two mags, you probably don?t need to concern yourself with the kickback scenario as related to the sniffle valve. You have enough flywheel effect from the heavy prop, and a weak enough starting spark with mags, that you shouldn?t have a problem with kickback unless your timing is off.
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV6/Used kit purchased 2021 building