Misfire

0320-A2B occasionally misfires during runup/mag check. Both mags. Rev up with lean mixture corrects misfire. Both rear cylinder's bottom plugs wet when pulled with one hour on regap and clean. Any advice ? Would using autogas be the problem ?

Do you mean the engine is missing or is it sounding like its popping (backfiring)? Could be running too rich, possible a mixture problem, but could be a whole host of things.

delete

Stan,

I ran auto gas for years (no alcohol) in my cubs and you are right about fouling! you could set the idle mixture with a warm motor and it would purr. starting cold (especially in the winter) would result in the symptoms you described! I would significantly lean the mixture with the engine running at aprox 1000-1400 rpm (until I saw rpm drop) then richen slightly, warm it up and continue with mag check, carb heat check and also right before takeoff I would if (suspected fouling) do a full power run-up and (lean to clean)

I haven't a clue the technical reason for this, except someone said that the flash point for auto gas is higher then for 100LL?? worked for me and I got many motors to TBO and no cylinder damage.

Hope this helps!

Tim

T.J. & Tim,
Thanks for the feedback. Autofuel I use has no alcohol. Remedy you suggest during runup seems to correct the misfire. Other information I received from local FBO also blames autofuel's flashpoint as being the main contributor to misfire during runup. Good to hear you've had good success getting engines to TBO using autofuel. That was a point local FBO was very negative on.

Stan,

Note)) that my experience with auto fuel was between 1970 and 1990 and I am sure the fuel isn't the same. There was no such thing as "unleaded" fuel and not nearly as many what ever they add to it now? I think it smells alot like a spruce tree??

Tim

Misfire during runup has been eliminated. Seems when using the autofuel from just down the road (nonbranded station) I always got a misfire. Leaning it for a couple of minutes during runup always cleared it up. I was trying to give my fuel business to the small station close to the airport. Going back to Shell station in town to refill my 55 gallon tank eliminated misfire when checking mags. The improvement was noticed on the first refill and has remained excellent on the past several refills. Same octane level, just something different about the fuel.

Stan,

Don't know if makes any difference but I always use Chevron Gasoline? I know a Mercedes mechanic that confirmed from "his schooling" that there is a "difference"?

Tim

Auto Fuel

There was an interesting article in Sundays Newspaper (Minneapolis Star Tribune) on auto gas. Seems like all brands come out of the pipeline and go into storage the same. When the gas gets transfered into a tanker truck it gets a "squirt" of whatever additives (Detergents/Anticorosives) each brand uses. So all the "GAS" starts out the same, it's the addmixes that make the difference.

Frank