O-360-A4M Cool/Cold Starting

[idahoflier]

Getting a good start is not always easy; especially with marginal ignition.

The correct mixture of fuel and air is needed.

A “ when all else fails “ system I’ve used on many different engines:

1. Full ( Wide Open) Throttle

2. Slowly close Throttle while cranking

3. When it fires IMMEDIATELY bring the Throttle back to 800 ish.


Wide open throttle is providing a lot of air. Lean?

Closing the Throttle has the effect of richening the mixture.


Together with variations in prime this may provide a good starting mixture.


IMMEDIATELY means just that. RPM should not exceed 1000.

No sleeping at the switch.

Thanks! Will try this first as there should be no flooding issues. If that doesn't work, will try Gary's method next.

 

[Eldorado]

Thought I would give my procedure for O360A1A, which I’ve used for 20 yrs. 1) normal first day start with normal temps- pump throttle 3 full pumps, close throttle, immediate start. 2) hot start, one complete throttle pump with immediate start(close throttle) 3) cold start- depending on temp, if under 50 degrees will prime once, twice, up to three times if really cold(30 degrees), then fully pump throttle 3x, close throttle and start immediately. I seldom ever prime unless under 50 degrees, always leave throttle closed, and hit the starter IMMEDIATELY after I pump the throttle. It has never failed me, but not recommending unless one has discussed with your mechanic. This is what mine recommended and it has always worked, but hit be quick with the starter, use close throttle, and prime seldom. If it below 30 I get preheat if traveling.

 

[Pinecone]

In cold weather, that fuel is more likely to coalesce on the induction and cylinder surfaces and be reluctant to ignite. At low temps, the fuel's vapor pressure falls way off. In the flight school we had much better starting by priming a couple of strokes, then pushing in a third stroke while cranking. That sends the fuel mist into the cylinder before it can fall out of the airstream.

The fuel and the engine are at the same temp, unless you preheat. Then the fuel will be colder than the engine.

Even if the vapor pressure is low, the fuel evaporates and more easily ignited.

The prime while cranking does help get a mist into the cylinder.

 

[Pinecone]

Getting a good start is not always easy; especially with marginal ignition.

The correct mixture of fuel and air is needed.

A “ when all else fails “ system I’ve used on many different engines:

1. Full ( Wide Open) Throttle

2. Slowly close Throttle while cranking

3. When it fires IMMEDIATELY bring the Throttle back to 800 ish.


Wide open throttle is providing a lot of air. Lean?

Closing the Throttle has the effect of richening the mixture.


Together with variations in prime this may provide a good starting mixture.


IMMEDIATELY means just that. RPM should not exceed 1000.

No sleeping at the switch.

Unless you prime to get to rich mixture, the amount of fuel delivered reduces as you reduce the throttle.

The true when all else fails (used to hot start a lot of injected engines) is to prime to flooded, then throttle Full, mixture ICO, then crank. When engine fires, you get to do the dance of not enough hands to get throttle to Idle, mixture to Rich, before engine RPM goes too high.

The one problem with this method is, if you WAY over prime, you can get fuel dripping and possibly a fire.

 

[MRC01]

... The one problem with this method is, if you WAY over prime, you can get fuel dripping and possibly a fire.

To elaborate on this: the primers spray near the intake valve, while the throttle/accelerator pump sprays in the carb throat which is much further upstream from the engine. It's easier to waste fuel and create a fire hazard by pumping the throttle, than by using the primer.

 

[Dan Thomas]

To elaborate on this: the primers spray near the intake valve,

Not true of all engines. The small Continentals (up to the O-200) spray the fuel into the carb "spider" manifold immediately above the carb. The C-145/O-300 shoots it into the manifolds where they exit the sump, far below the cylinders. The O-470 sprays it into the intake runners, again far below the cylinders.

Lycomings spray it into the intake ports. Some large Continentals do that, too: there were a few injected 520's that had a primer system. Cessna 185.

 

[MRC01]

To elaborate on this: the primers spray near the intake valve, while the throttle/accelerator pump sprays in the carb throat which is much further upstream from the engine. It's easier to waste fuel and create a fire hazard by pumping the throttle, than by using the primer.

Not true of all engines. The small Continentals (up to the O-200) spray the fuel into the carb "spider" manifold immediately above the carb. The C-145/O-300 shoots it into the manifolds where they exit the sump, far below the cylinders. The O-470 sprays it into the intake runners, again far below the cylinders.

Good point. They do on my engine, but each pilot should follow the primer lines on his own engine and determine this.

 

[idahoflier]

Yesterday was my first opportunity for experimentation. Unfortunately, as noted earlier, we're experiencing unseasonably hot weather and as usual I didn't get to the hangar until 1230. OAT was 93ºF and hangar/engine was 82ºF.

Slowly opened throttle to full. Mixture idle-cutoff. Engaged starter and the engine instantly fired. It all happened so fast I instinctively disengaged the starter and the prop stopped before I could enrich mixture. Second attempt, mixture ⅔ rich, throttle ¼" opened. Took 8 seconds of cranking and engine fired.

The above makes me think in warm conditions things are more rich than needed. Also it sure seems like ignition is probably OK. I'm flying tomorrow (earlier) and conditions will be closer to normal temps though still not even close to the cold temps I'm concerned about. I'm going to try one throttle pump and mixture ⅔ rich and see what happens.

I also contacted Air Plains and unfortunately it sounds like they sold out of the primer kit (sounds like a real popular item, guess I'm not alone) and due to some supply issues it's no longer available. Sounds like they're working on selling it again with a different BOM so hopefully it will be available again in the future.

Thanks for the discussion, appreciate the comments!