ExtraKatana

ExtraKatana

Well Known Member
We all have dealt with Hot starts and I know what causes those. We have a high-time (1800hr)O-360 (with compressions in the low 70's) that runs well once it gets started. It won't "hardly" cold start and in 1300 hrs flying time I've never had to deal with it. Maybe I'm lucky....
I'm talking hard to start at even 60F. Much worse at 40F.
Tried....only pumping throttle/one shot prime and pumping/two shots prime and wait a minute/three shots prime.....Great......now I'm flooded. it just doesn't want to start until 3-5 minutes of attempts and starter cool-down time. I noticed a peanut gallery forming last attempt and embarrassment has led me to this post.
Now get above 80F and it trips right over.

Is this a product of a high-time Marvel-Schebler? Just a product of cold fuel not wanting to atomize for proper stoichiometric pressure? Suggesstions? Remedies?:confused:

I do pre-heat the engine in the hangar. Embarrassment mixes with a little worry at distant ramps.....where I don't have the option of pre-heat......or access to a battery charger.:eek:
 
I have little experience of your kind of cold, except when I have been in Ada......and it snowed :eek:

My suggestion would be check a bunch of things first.

Mags in good order?
Plugs, if massive electrode, gaps at 0.016-0.018" and the resistance is below 5000 ohms.
Do not use the primer. I hate them for one thing and mainly as you describe.

Start with the mixture in and the throttle open a bit, get the propellor turning first, this gets some air through the carby and then while it is rotating nicely start a few quick throttle pumps all the way in and 75% the way back out. It should start on the second or third pump.

What you are trying to achieve is atomised fuel to all cylinders and not puddles in one.

The same process works for hot starts.
 
There is not a single carbureted engine with an accelerator pump, a starter and good battery I can't start cold AFTER I give the throttle two quick pumps after two blades have passed, and commit to not stop cranking. I haven't used a primer in over ten years except in a Cub or Champ.
 
Operating up here in the Great White North, we do have some experience with cold starts (just a little!), and I've had 3 planes with O-360's, so?.my technique is a few shots of prime with the boost pump on (varies with the installation; my Cherokee and Tiger needed 3-4, the RV likes 5), crack the throttle about 1/4" and crank. Advance the throttle if it doesn't fire on the first 2 or 3 blades. I haven't pumped the throttle in decades. I used to, but I (and others) have found that it greatly increases the odds of flooding and/or backfiring. Good "plan B" if your primer isn't working, mind you, but I haven't had to turn more than a couple of blades before firing up for many years using the technique described. Currently I am starting up with no preheat after pulling the aircraft out of a hangar which we keep at 50 degrees F. Before we heated the hangar, I would preheat when temps were below freezing, and with my previous planes, they lived outside on the ramp and were preheated in cold temps. I would not consider 60 degrees cold, and barely would consider 40 cold; I've certainly started many times in the past at 40 without preheat and without any problems, although I would prefer not to. If these techniques don't work for you, then I would start looking at the mechanicals.
 
Other methods may work with some carbureted airplanes but briskly pumping the throttle 2 - 4 times (depending on how cold it is), only while cranking, will start any carbureted Lycoming as long as the carb is equipped with an accelerator pump.

As already mentioned, technique wont help if there are issues with some of the engine systems.
 
I have heard check the mags to see if they are in good order.
What is the correlation between temperature/Mags/Cold Starts? Seems to run fine after started. What are we checking for?

Checking plug gap is an easy-enough

What other action items?

I am fairly certain I have tried all the methods described with primer and accelerator pump.

Warm ambient = easy start Cold ambient = hard start

Thanks!
 
My guess is the impluse coupler on the starting mag is bad. I had an 0-320 that the impulse coupler would only work on the first turn of the prop. After that it was futile to crank anymore. Replaced the mag and all was fine. Listen for that clacking sound when cranking. If you don't hear it, the coupler is probably bad.

Roberta
 
question on accelerator pump?

if i install a primer pump in my project i will be shooting fuel right by the intake valve what does an accelerator pump on the carb do? i would prfer not installing a primer but in my 0-320 it starts better with the primer but i was not cranking the engine and then the two pumps i did it prior to cranking so maybe that was why.
 
robertahegy said:
My guess is the impluse coupler on the starting mag is bad. I had an 0-320 that the impulse coupler would only work on the first turn of the prop. After that it was futile to crank anymore. Replaced the mag and all was fine. Listen for that clacking sound when cranking. If you don't hear it, the coupler is probably bad.

Roberta
Click to expand...

I'm with Roberta. I have had a case where an impulse coupler was greasy/dirty and when it got cold, that stuff made the impulse coupler stick and not work. Warm it was fine. I'd go after mags, especially if they haven't been recently serviced.


....and as everyone else has stated, throttle pumps WHILE CRANKING ONLY.
 
Been there, change the spring

Had the same problem, changd the spring in the Impulse coupling and starts just like Bob says.
 
And...

If it is the mag impulse coupling and it decides to come apart, it could ruin your whole day. I would take a look ASAP.
 
Interesting reading about the mags and people's experience. These poor things cop a hard life so it was an obvious inclusion on my list of things.

This is probably a good time to remind people that hey have a 500 hour service interval for a reason. They are strong and reliable, but they too need a little TLC from time to time.

Bill V
Don't waste your time and money, adding weight and including a possible point of danger from leaks, either fuel out or intake in.
 
Impulse coupler?

From what I have read/heard, I do not have the symptoms of a sticking impulse coupler.
Sticking couplers try to start the first couple of blades then never do start after.
My symptom is the exact opposite.
I might have a timing situation however that has affected the advance/retard of the impluse coupler.
Hmmmm.
 
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