Huh? Why is it far easier to start them inverted? I always have to flip mine over and that can be a problem cause I uauall fly alone.
Because it's almost impossible to flood them from choking. What happens with uprights, many times, is that if you choke them enough to get fuel into the cylinder, there's too much fuel in the crankcase. When it pops, it sucks all the fuel out of the case, and kills it rich. Inverted, the issue is usually getting enough fuel in them by choking, since it tends to run out on the ground if you remove your finger.
Technique is everything. You have to work it out for each engine, but it's something along the lines of this:
1 Fill tank, put finger over venturi, pull through 3-4 times. This gets fuel up to the venturi.
2 Flip through forward as you remove your finger from the venturi. The idea is to remove your finger as the engine is sucking in air, so it will suck in the fuel now in the venturi
3 Flip through forward 3-4 times to aerate the charge and get clean fuel and clean air in the cylinder. Once you know what to listen for as you flip it, you will be able to hear whether or not there is sufficient fuel. If not, pull through again, flip forwards some more until it sounds right.
4 WHILE HOLDING THE PROP, attach the battery.
5 Back-bump up against compression. Don't flip through backwards, just sling it backwards so it comes up on compression smartly when your finger is off the prop. You don't have to whack it hard, for most current engines just twisting the spinner is sufficient. Repeat if necessary. Your finger should be off the prop when it hits compression.
6 Engine will likely start
7 If it doesn't problem is likely not enough fuel, pull it through some more.
More choking will be required on the first run of the day, or when it is cold. If the engine is still warm from previous flight, it may require no choking depending on which engine it is. It's very hard to over-choke it but if you do, remove battery, pull it up on compression, hold it, then turn the airplane with the exhaust port facing down, and then release the compression and rock it back and forth. This will remove excess fuel. Then put it back on its feet, attach the battery, and back-bump, should take off in a few tries. It takes more fuel to start with a back-bump than it does with a forward flip through.
If the engine is hot and you over-choke it, it can get "shrinky piston syndrome" when cold fuel sloshes on the back of the piston and shrinks it, but not the cylinder, and the compression goes away. The solution is to flip it forward through compression many times to distribute the fuel and heat evenly, and the compression will come back.
Note that someone should hold the airplane ALL THE TIME when the engine is being choked, etc. With any current AAC/ABC engine there is a real chance that it will kick or start without the battery. Particularly if you get your choking technique just right, it will have a perfect mixture and start very easily. I have had them start from merely rocking back on compression from the weight of the piston. It's more prone to happen when it's really hot* but could happen anytime.
Very occasionally, with low-compression engines and when it is hot, conventional flipping will be required. There's also an advanced technique that involves flipping through compression forward while simultaneously holding your finger over the venturi, and then removing it as the engine starts. I have had to do that occasionally on my tired 40VF on back-to-back runs.
With piped engines, you have to get the oil that has run down into the engine from the pipe out of them on the first run of the day, and in that case I do usually flip them upside down and *prime* them (not choke).
Brett
*at the 1993 NATs in Lawrenceville, it was brutally hot all week, and my 40VF started without the battery repeatedly at step 2 or 3 above - I mean just about every time, including my official flights. The first time it happened, Ted was impressed that I was able to get my fingers on the spinner fast enough to stop it before it got to full crank. After that I signalled before I started and got it going while I was on the clock.