We had another reminder of why you have your holder *restraining the airplane* while you choke or aerate your engine "prior" to starting it. I was flying a back-to-back flight, the engine was warm, and I overdid the choking a bit. This led to classic "shrinky piston syndrome" - a first in 25ish years running the RO-Jett 61. The fix is to remove the battery and flip it forward a bunch of times to equalize the temperature.

   A few flips in, and the engine popped and then started without the battery connected. Fortunately, Dennis was in place, restraining the airplane, for just exactly this possibility, no problem, and I just flew the flight. The engine was not inordinately hot and the weather was pretty normal spring weather, maybe 85 and clear.

  Point being - any time there is fuel in the engine, it might pop or start, battery or not. This is not a new phenomenon, in the past with the various junky ringed or slug-piston engines, it would on very very rare occasions, start without the battery. When we started running modern engines (AAC or even more so, ABC engines), this became a rather common occurrence. At the 93 NATS, in the boiling heat, my 40VF would start while choking every single time, including before signalling for start on an official flight. Ted and I gave up trying to choke it and just signalled, attached the battery,  and flipped it with my finger over the venturi. Instant every time. AAC engines seem far less prone to it, I think because they do not tighten the fits when cold, it's more or less constant with temperature. ABC is tight cold and loosens to normal clearance when running.

   My PA61 used to do this now and then in some surprising conditions, as I mentioned, this is the first time it has happened with any of the 3 RO-Jetts I have used since 2002.

   So - when starting - *have someone hold the airplane any time there is fuel around*, *you hold the prop stationary off TDC when you attach the battery*, and in general treat it like a hand grenade with a unknown delay anytime you are prepping it for flight. Obviously, do not casually turn it over when there is fuel in the tank.

    Brett

Glad you can still count to 10...

I've had that happen with a Baby Bee .049 before, but not a larger engine.

Fly safe!

Steve

I guess you would be safe with a McCoy red head 35, because it takes an electric starter to start them.  Maybe they didn't know it back then, but it could have been the safest engine made?   

It can also happen with a ringed engine and no nitro.
To me it happened last time when I was walking to circle in a contest in Italy, and just casually turning over the prop to mix the prime.
Yep, be careful. L

Back in 1969, I had a flying buddy that was a first class engineman (diesel mech) on the USS Cromwell, DE 1014.. We were in the machine shop and he had just cleaned up a McCoy .049 Diesel engine.. He was holding it in  his hand and absently flipping the prop when it started,, I wish I had a camera to catch the look on his face.
Big irony, a crew of 176 and 5 CL builder/flyers.

GREAT ADVICE BRETT, I WILL SPREAD THE WORD. SOMETHING SIMILAR HAPPENED WHEN A COMPETITOR AT THE CANADIAN TEAM TRIALS ATTACHED THE GLOW DRIVER TO THE ENGINE AND A SECOND LATER THE ENGINE STARTED BY ITSELF! LUCKY FOR HIM HE GOT HIS HAND OUT OF THE PROPS WAY, AND I WAS HOLDING THE PLANE IN PLACE.

Quote from: Kevin K on May 17, 2026, 04:51:47 AMGREAT ADVICE BRETT, I WILL SPREAD THE WORD. SOMETHING SIMILAR HAPPENED WHEN A COMPETITOR AT THE CANADIAN TEAM TRIALS ATTACHED THE GLOW DRIVER TO THE ENGINE AND A SECOND LATER THE ENGINE STARTED BY ITSELF! LUCKY FOR HIM HE GOT HIS HAND OUT OF THE PROPS WAY, AND I WAS HOLDING THE PLANE IN PLACE.

   Yes, you should always hold the prop when you attach the battery - that is far an away the most likely time for it to start unexpectedly.