I used to part-own a Yak52, with the same Vendeneyef M13P engine. Starting routine is back in the mists of time, but I did publish an article on the aeroplane in 'Pilot', and I reproduce the engine start sequence below. I was religious about 'pulling though' the prop and removing the drain plugs from the lower cylinders to preclude hydraulic oil lock, but I never heard of this happening through over-priming; that usually led to setting the nosewheel tyre on fire!
After turning on the main air valve, setting the various switches, priming the engine, and pumping up fuel pressure it’s time to start. Coaxing a big radial engine into life is part of the joy of operating an aeroplane like this, and is a bit of an art. Correct priming technique is important; not enough, and it won’t start, too much and you risk a fuel fire. Winter starting of a cold engine requires the prop to be pulled through in between primes – more easily done with the assistance of a ground helper.
I call “clear prop”, while holding my right arm vertical and rotating my extended forefinger in the air for a couple of seconds as a visual signal for those out of earshot – if a Yak is starting up anywhere near you, you need to know about it before it happens. I hold the stick back in the crook of my right arm (old taildragger habits die hard) with my forefinger on the start button to the left of the panel, having flicked up its cover. My left hand rests on the one-third-open throttle lever. A glance round to check all is clear, and I press the button. There’s a loud ‘pop’ followed by an asthmatic wheezing as compressed air is admitted to the cylinders via a pneumatic distributor to turn the engine. The prop jerks slowly round a revolution and I flick the mags to ‘1 + 2’ (you really need three hands for this) and one cylinder fires. I release the start button and pump the throttle to keep the prop turning. More cylinders join in with a sudden roar, and clouds of smoke stream from the exhausts. The prop dissolves into an invisible disc, blowing the smoke instantly backwards – but it’s not sustained and the engine dies, clattering round slower and slower, the prop becoming visible once more. I pump the throttle again, my right hand going to the primer. But before I can decide whether to prime or not, several cylinders fire up raggedly accompanied by more grey smoke which is blasted under the wing by the propwash. The engine dies again, the prop slowing, but only for a second or so. With a glorious throaty roar all the cylinders report for duty, and this time as though they mean it. The engine clears its throat with a cough or two, becomes self-sustaining, and settles into smooth regular song. The battle is won and I snap the starter button cover down.
A friend described a Yak start up as ‘biblical’ – lots of noise, lots of smoke, the ground shaking, and the smiting of lesser objects. This latter point is one to watch; anything much more than idle power can blow over a light aircraft in the propwash.
Now we have all nine cylinders rumbling away contentedly, oil pressure in the green, RPM at 50% as we wait for the oil temperature to rise to at least 25 degrees C before taxy. In winter with a cold-soaked engine, that can take fifteen minutes or so. The big radial makes a glorious sound as I complete the after start checks and do the radio calls while standing by to open the cowl flaps as the cylinder head temperatures rise faster than that of the oil.
SSD