O-540 Starting Question

N936BW

During the failed start procedure, it says to clear the flooded engine by rotating the engine approximately 10 revolutions while opening the throttle slowly. Two questions...

1. How far do you open the throttle?
2. How does opening the throttle clear a flooded engine; seems counter intuitive?

Thanks

Scott Sherer

We're going to need specific information here. What year and model of airplane and engine. What is "it" that you refer to?

N936BW

67 PA-32 6/260 with an O-540. The POH says:
If the engine fails to start at the first attempt, another attempt should be made without priming. If this fails, it is possible that the engine is overprimed. Turn the magneto switch OFF, open the throttle slowly, and rotate the engine approximately ten revolutions with the starter.

Scott Sherer

Hey, thanks for the help!

Guy_pere

I never us the primer on my 260. I just pump the throttle 3 times and off she goes.
Hope this helps.

N936BW

Still hoping for some insight into this.

Guy_pere

I do very short hops in my 260 (9 mins is my normal flight time).
Hundreds of starts a month.

The 260 is one of the easiest starting engine I have sat behind.
So possibly:
you are flooding it.
your mag timing is off.
you have a broken primer line.
Plugs gapped incorrectly

Do you have problems all the time or just hot starts?

N936BW

I guess you misunderstood my post. I never said I have been having problems starting my engine. She cranks like a champ each time. I was just trying to figure out the failed start procedure and make sense of it.

Scott Sherer

Thanks for the clarification. Hopefully our member participants can re-enter the conversation. Thanks again.

N936BW

Well... I think I actually stomped the chumps with this thread. Never thought I'd see that happen. So let me try a new one. Still centered around start up procedures.

1) Why is it necessary to let the prop spin one rotation before turning the Mags on and;

2) Why do you only go to the left mag first till it starts then to both?

Ok, fellas, take a whack at these!!

Scott Sherer

Digging waaaay back in my aviation career which starts in 1964 I can honestly say that I've not heard of either of these. I'm looking forward to other feedback. Most interesting!

kzadora

I am not sure about #1, but #2 is related to “impulse coupling” that boosts the spark and changes magneto timing (delays ignition) during the start, which involves very low RPM initially. Impulse coupling is typically only installed on one magneto, usually left.

N936BW

Interesting. Makes sense. Thank you.

Don3950

To your original question- opening the throttle and putting mixture at idle cutout allows more air to enter the cylinders helping “dry” them out of excess fuel. Same as we did with carbureted cars. Remember holding the pedal to the floor?

To your last question -
1. I assume you still asking about flooded engine starting? Since normal starting procedure does not involve cranking before turning on left mag.
2. Impulse coupling is on left mag that retards timing and boosts output momentarily creating a hotter spark to assist in starting. Impulse coupling is only active at very low RPM, usually under 500 RPM.

67 PA32-260. O-540 E4B5

Don3950

To your original question- opening the throttle allows more air to enter the cylinders helping “dry” them out of excess fuel. Same as we did with carbureted cars. Remember holding the pedal to the floor?

To your last question -
1. Are you still asking about flooded engine starting?
2. Impulse coupling is on left mag that retards timing and boosts output momentarily creating a hotter spark to assist in starting. It too helps avoid a “kick back”. Impulse coupling is only active at very low RPM, usually under 500 RPM.

N936BW

Thanks Don. That makes perfect sense about opening up the carb to dry the cylinders IF you pull the mixture off.
Problem is that my POH doesn't say to do that. Interestingly, I have a copy of a 1968 Cherokee 'B' and the start sequence is completely different as well as the flooded start procedures; which in fact DOES say to pull the mixture off.

As for question #1 about rotating the prop; that is from the normal start procedure straight out of the POH as well.

Don3950

That’s odd. My 67 PA32-260 only has a “airplane flight manual” as most early aircraft did. Is your POH from Piper or an aftermarket one?

Scott Sherer

The POH is a legal document that is delivered with the airplane. Basically, it's an airplane flight manual with sections included for any additional equipment or changes to your particular aircraft.