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24 Feb 2022 12:37 #3409

I have a PA-28/140 and it is sometimes hard to start after sitting for a while in the cold of winter. Takes quite a bit more prime to get it going. Once running, it settles down fine.
Never an issue in the summer. Perhaps just a weather/winter event.

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  • Doug Linville
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19 Nov 2021 17:15 #3253

Thanks again for your help.
I think the temperature has something to do with the problem. Well try to keep that in mind when starting.

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18 Nov 2021 17:31 #3249

Doug,
Red text is the system; every reply is in red until it's posted--then it's black.
The primer system for your O-540 consists for little spray nozzles that are installed in 5 of the 6 cylinders. The parts diagram shows that the cylinder closest to the firewall on the pilot's side does not have a primer spray nozzle.
Check to see that all five nozzles are installed.
Does the amount of priming required to start the engine change at different times of the year? I ask because the fuel sprayed in the summer should atomize and vaporize better than the fuel sprayed in colder months when atomization is less active. It's the vapors that ignite, not the liquid fuel.
Could this hard(er) starting problem be more related to outside air temperature changes than an actual engine or priming problem?
It's relatively easy to check primer nozzles to see if they're clogged. Remove each nozzle from the cylinder than connect it to the tube that feed fuel to it. Be careful not to bend the tube aggressively. To minimize the tube bending, I would slide a rubber tube over the end of the nozzle and put the other end in a small jar. We always used baby food glass jars. So 5 nozzles feeding into 5 glass jars through rubber tubes. Then apply three or four good primer strokes. Don't be in a hurry to push the primer plunger forward; pull it all the way aft, and after a few seconds push it forward. See if each nozzle is delivering the same amount of fuel. If one or more isn't find out why.
But really, it doesn't sound like there's a real problem. It sounds more like your priming process needs to be amended.
Remember it will take more priming in cold weather.

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  • Doug Linville
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18 Nov 2021 12:01 #3248

Steve
Thanks for your response and your time.
The problem is "newish".
When the engine starts, I would say it is a clean start although also, at times, I would say it hits hard, a very sudden start. Hope that makes some sense.
Haven't checked the plugs yet. The airplane had its annual in June and the plugs were checked then.
I keep the log books in a safety deposit box so I haven't checked about the mag overhaul. This airplane is generally flown about 25-40 hours a year. I doubt the 500 hour mag check is overdue.
The idle speed is 600-700 RPMs and is smooth.
Now for priming:
When the engine is cold and has sat for several days, I usually begin with 4 pumps of prime with the throttle cracked. If no response with a few revolutions, I stop and add an additional pump. If no response, I stop and add another pump until the engine starts. Usually with only one additional pump.
I have owned this airplane for 19 years and never heard the vibrator. A few years ago I had a similar starting problem and the mechanic did replace the box.
I recently installed 2 Garmin G-5s and a GFC-500. Not anxious to install the electronic ignition right now, although, the avionics don't help much if the engine doesn't start.
(not sure why my text is red)
Doug

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17 Nov 2021 17:22 #3243

Hi Doug,
First I'd like you to tell me if this is new, newish, or it's always been that way?
And, when the engine does start is it a "clean" start? In other words, does it immediately settle into smooth running, or does it take a little time before it's running smoothly?
There are a number of maintenance items that will affect "reluctant" starting in a carbureted engine.
Have the spark plugs been measured to get a reading on the electrical resistance between the contact in the barrel and the center electrode? If it's over 5000 ohms, replace the plug;
Is the plug gap correct?
Are the magnetos due for a 500 hour (since last inspection) inspection? If not, they are probably not putting out the maximum strength (hottest) spark possible.
Is the idle mixture and speed set correctly at the carburetor?
If all those items are up to date, what is your priming procedure?
In the past I found that one of my magnetos had a partial electrical open in the coil. The result was very hard starting (it was the left magneto) but good mag checks. I sent the magneto Aircraft Magneto Service ( www.aircraftmagnetoservice.net ) where they discovered this unusual fault and fixed it.
I believe that the set up in the 250 has one impulse coupling that's installed on the left magneto. Th impulse coupling is designed to generate a hot spark during starting, and move the spark from the normal 25 degrees before top dead center (TDC) on the compression stroke (where it is during all other phases of engine operations) to 5 to 10 degrees to make starting much easier.
The ignition switch should be wired to ground out the right mag when the key is in the start position. If it isn't, or if the impulse coupling is worn that can create hard starting problems.
Your engine may be equipped with a starting vibrator to assist in starting. This device generates a shower of sparks when the key is move to the start position. You should hear it buzzing. If you can't hear it, there is a procedure in the service manual for checking the operation.
As you can see, there are many pieces of the hard starting puzzle.
I too had a hard starting problem. That spurred me into installing an Electro Air electronic ignition system on my engine. Since installation I've never had a starting problem, my engine idles much smoother and I believe my engine is operating more efficiently than it used to. It's burning less fuel at the same power settings.
Let me know if this helps; and let me know if I can help further.
Steve

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17 Nov 2021 01:35 #3242

Five to seven for me if I do my part correctly. TIO540.

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