Hard starting hot O-540

[Paul Klouda]

Greetings All,

I've got a ~450 hour factory reman O-540 on a 1964 PA24-250 that is giving me fits especially on hot starting. Example: Fly in and shut down after a 30 minute flight grab a $100.00 hamburger and then 30 - 45 min later fire up and launch. What was the usual start up procedure does not seem to cut it anymore. I would turn on master, boost pump, get positive fuel pressure, turn off boost pump, pump the throttle once or twice and then crank starter. In a few revs the engine would fire, and I would be on my way. Roll forward to now that does not work. Sometimes, I now have to throttle in and mixture to cut off turning the starter until I get the engine to catch and then quickly pull the throttle back and push the mixture in. Again, this is a normally aspirated engine, not fuel injected. I am not getting any back firing or other tells. The starter will sometime stall during a rev and I need to jog it to get it moving. I replaced the battery (Concord 35 extra crank power) no help, (have copper wires, Boggert) checked and tightened all the connections in the system and have new (less than 300 hours) on the mags and wires. Even starting cold using the prime can be a bit challenging. Once she's started I have had no problems.

Sorry to go on so long but I hope this paints the picture.

Any suggestions or input?

Thanks,

Paul

[md11flyer]

Paul, It could be a number of things. FIrst do you have the impulse coupling in your mag(s) or do you have the shower of sparks?
I know you said the mags have only 300 hours since overhaul, but when was the breaker points last checked/set? If you have the impulse coupling(s) do they make a
positive clack when you turn the prop over by hand? Because you have a problem that is showing up when your engine is cold and of course more so when hot, I would suspect a
weak spark . When were the spark plugs last serviced? I am pointing toword ignition because you mentioned sometimes the prop would "stall" during the cranking.
That indicates to me anyway that there is enough fuel but maybe an incorrect igniton, be it impulse coupling, points or internal timing of the mag.

If you have the impoulse coupling(s) then turn over the prop by hand, if you get a good clack(s) go further in the log books to check when the mags were last serviced in regard to breaker points and
timing. If you have a weak clack from the impulse coupling you might want to go further with replacing it. If you have the shower of sparks then you might want to check the ouput from that as well as internal point check setting.

Hope this helps,
Gary

[Chip Sylverne]

[Paul Klouda]

Thank you Gary,

I have slick impulse coupling. The "clack" is still loud and constant. (I am going to have the breaker points checked at annual). I did remove and inspect my plugs yesterday. Many of them showed the signs of wear the football shaped electrode and increased gap. None were oily and only one had a bit of lead build up around the insulator (bottom jug 6). The result, I replaced my plugs and voila back to quicker, better starts. My prop still stalls sometimes (after a partial turn on the first crank) when hot, but I jog the key and it pulls through 2 or 3 revs then fires. I have a Lamar starter (about 10 years old) and will be looking to install a SkyTec this annual. That should clear up the stall issue.

Thanks again for the input,

Paul

[md11flyer]

Paul,
You are welcome, Yes a lazy starter can definitely cause poor start performance.

Gary

[MV Case Jr]

Paul ,
You don't say where you live ( I'm in Texas ) but in the summer time a hot O-540 will act like a new engine , i.e. not want to turn over ( stall) . How old is your battery ? I use a battery tender ( not a charger ) and don't have that problem any more .
I also use the "flooded" procedure on hot starts . Mixture - rich , 3 shots of prime , Throttle - cracked , but slowly moved toward open as engine turns , then back to idle when engine catches . Fly safe .

Marty