Help with the impossible start...Cherokee 140
I have a 1973 Cherokee 140 that never gives me issues in its home state of California.
Normal start - 2-3 pumps of primer, fuel pump on, throttle open 1/4", mixture rich, and it starts right up.
Hot start - 1 pump of primer, throttle open a little more than 1/4", mixture about 3/4 rich and it starts right up.
Cold start - 3-4 pumps of primer, throttle open 1/4", mixture rich, starts right up.
I flew to KAPA (Centennial CO, near Denver to spend a week with family, and of course, the damn thing won't start. It's about 0 C, 5400 feet. Tried 3 shots of prime, a little more than normal throttle, and mixture about 1/2 open, a couple of coughs. Tried multiple times, no dice. Added another shot of primer, nothing. Had the FBO guys tow it inside a heated hangar while I ate breakfast, came back, still nothing. Tried just about every conceivable combination of mixture and throttle, nothing. Ended up flooding the engine, so then I tried the full throttle, mixture cutoff with a jump start connected to my now worn down battery, not even a cough.
Luckily, I don't have to leave for another couple of days, but I need advice on how to not have this happen again, and what I need to do with the flooded engine and carb. I can have the engine preheated, I can have the plane stored inside, etc. but if I'm super flooded (gas dripping out when I left it), I also need to know if I need to have a mechanic go in and 'unflood' the carb or the cylinders. If I remember correctly, I'm only priming one cylinder in this engine.
Thanks for any and all advice!
Normal start - 2-3 pumps of primer, fuel pump on, throttle open 1/4", mixture rich, and it starts right up.
Hot start - 1 pump of primer, throttle open a little more than 1/4", mixture about 3/4 rich and it starts right up.
Cold start - 3-4 pumps of primer, throttle open 1/4", mixture rich, starts right up.
I flew to KAPA (Centennial CO, near Denver to spend a week with family, and of course, the damn thing won't start. It's about 0 C, 5400 feet. Tried 3 shots of prime, a little more than normal throttle, and mixture about 1/2 open, a couple of coughs. Tried multiple times, no dice. Added another shot of primer, nothing. Had the FBO guys tow it inside a heated hangar while I ate breakfast, came back, still nothing. Tried just about every conceivable combination of mixture and throttle, nothing. Ended up flooding the engine, so then I tried the full throttle, mixture cutoff with a jump start connected to my now worn down battery, not even a cough.
Luckily, I don't have to leave for another couple of days, but I need advice on how to not have this happen again, and what I need to do with the flooded engine and carb. I can have the engine preheated, I can have the plane stored inside, etc. but if I'm super flooded (gas dripping out when I left it), I also need to know if I need to have a mechanic go in and 'unflood' the carb or the cylinders. If I remember correctly, I'm only priming one cylinder in this engine.
Thanks for any and all advice!
Comments
All the fuel pump does is make sure there's fuel in the fuel bowl of the carburetor.
The primer jets vary in number - anywhere from 1 to 3. It is probably possible to install as many as all four. See your mechanic for details, it isn't rocket science. That will get fuel to the cylinders for starting.
It sounds though to me, that your problem is probably spark. When is the last time the plugs were pulled, cleaned and gapped? When was the last time you had the magnetos inspected and their internal timing properly set? Do you have a magneto key switch with "off - R - L - Both" and a completely separate starter button, or does your keyswitch incorporate a push to start or turn to start position? On the simpler magneto switch variety, starting should be accomplished with just the "L" position, since that's the mag with the impulse coupling on it.
If you slowly rotate the prop by hand, do you hear a sharp, "snap" as the magneto coupler engages? If not, have your mags pulled ASAP.
If you have fuel and air in the cylinders, all you need is compression and spark of sufficient power and correct timing. It will start, no doubt. One of those elements is missing from the equation and it is just a matter of figuring out which one. Cold starts are particularly difficult for a number of reasons, poor fuel volatility, less power from the battery, thickened oil and if your spark system is weak, then it too will contribute to your ills.
My old Cherokee 180 suggests priming and then rotating the prop by hand a couple of turns, then starting. I think it sucks a little gas from the primer jets into the cylinders, lets it sit a few seconds to volatilize before hitting it with spark.
Frosted plugs can also be a bear:
"Another cold start problem that plagues an unpreheated engine is icing over the spark plug electrodes. This happens when an engine only fires a few revolutions and then quits. There has been sufficient combustion to cause some water in the cylinders but insufficient combustion to heat them up. This little bit of water condenses on the spark plug electrodes, freezes to ice, and shorts them out. The only remedy is heat. When no large heat source is available, the plugs are removed from the engine and heated to the point where no more moisture is present."