Starting O-360 Without Primer

[xrs135]

Starting procedure for the carbureted O-360 in my M20C without a primer installed...

 

-Mixture full rich

-Fuel pump on

-Pump throttle 2 times (3+ if cold)

-Fuel pump off

-Throttle 1/4"

-THEN crank engine

 

...If this is such a terrible technique (due to risk of fire if there is a backfire), then WHY is the the procedure listed in both the POH, and the Lycoming Operator's Manual? You'd think over the years the Lycoming would come out with some sort of alternate starting procedure? 

 

Honestly, I've been starting the plane with this technique without any issues... but after reading up on the matter, I think I'm going to start trying out the fuel pump off, mixture rich, and throttle pumping while cranking technique as a means of priming and see how that works out for me.

 

Opinions?

[rbridges]

that's how I did it in the Cherokee and now the Mooney.  What have you read?

[garytex]

I like the pump while cranking scheme, less raw gas in the lower cowl on carbed engines.

[xrs135]

Well... Without getting into too much detail, yes, It's like garytex said. Many people believe that by pumping the throttle without turning the engine over at the same time is a SERIOUS safety issue, because you essentially just get a massive puddle of raw fuel sitting in the airbox due to the way the carburetor is mounted. By pumping the throttle while cranking, there is enough suction being created to keep the fuel from puddling and draw it up into the engine instead. The fear is that the fuel poses a huge engine fire during start threat if there is a source of ignition introduced to all the sitting fuel.

[Hank]

I follow the procedure in my Owners Manual. It has worked flawlessly since 1970, and I've not heard of anyone with a carbureted Mooney having an engine fire while cranking since introduction in the 50s. Especially in cold weather, it's much better to put fuel into the carb early and give it time to evaporate before cranking, else you get to crank and crank and crank . . .

Has anyone heard of a carbed Mooney WITH a primer? Where does a few shots of primer put the fuel, compared to where pumping our throttle puts it? Methinks someone has been listening to people who fly Brand C planes that have primers, which I also used when flying those as a student. What do those people know better than both Mooney and Lycoming?

EDIT: reviewing the OP, I've been not paying attention and doing it wrong, like this:

-mixture Idle/Cut off

-fuel pump On

-let fuel pressure stabilize

-fuel pump Off

-pump throttle (2x warm weather, 4-6x cold weather)

-throttle 1/4"

-crank

Need to review my procedure and double check the Book.

[bonal]

Once I got used to not having a primer I get great starts every time on 2 blades. Same procedure as you Hank only I have mixture in then pull to lean as soon as she starts. Hot starts even easier just start to crank and feed the mixture back in. When I first bought the plane I was having trouble starting it led me to Mooney Space. The rest is history.

[rbridges]

Not that it gets super cold here, but you guys go up to 4-6 pumps in lower temps?

[BigTex]

Once I got used to not having a primer I get great starts every time on 2 blades. Same procedure as you Hank only I have mixture in then pull to lean as soon as she starts. Hot starts even easier just start to crank and feed the mixture back in. When I first bought the plane I was having trouble starting it led me to Mooney Space. The rest is history.

This is also how I do it.... Mixture full rich, boost pump on until I have max fuel pressure (~5 psi), two pumps of the throttle and start the engine. Always Starts within one turn. Then lean to around 2 GPH. On really cold days, you might have to pump the throttle a couple of more times.

[orionflt]

Well... Without getting into too much detail, yes, It's like garytex said. Many people believe that by pumping the throttle without turning the engine over at the same time is a SERIOUS safety issue, because you essentially just get a massive puddle of raw fuel sitting in the airbox due to the way the carburetor is mounted. By pumping the throttle while cranking, there is enough suction being created to keep the fuel from puddling and draw it up into the engine instead. The fear is that the fuel poses a huge engine fire during start threat if there is a source of ignition introduced to all the sitting fuel.

you do not get a puddle of fuel in the air box when you pump the throttle without cranking the engine, in fact when you pump the throttle the fuel is introduced into the intake plenum and it immediately vaporizes. it is true that if you prime too much you will get to the point that the fuel air mixture in the plenum is such that the fuel can no longer be vaporized, at that point the excess fuel will drain down into the airbox where the airbox drain will keep it from puddling.

when you try to start the engine by pumping the throttle while you are cranking the engle all you are effectively doing is extending the amount of time the engine takes until it can create the proper fuel air mixture to start. this means your starter is working longer and the amount of time the engine turns with only residual oil on the surfaces increases.

if there was a fire issue with the starting procedure, Lycoming and the aircraft manufacturers would have changed it years ago. if you want to worry about too much fuel doing damage or causing a fire in the engine, then worry about getting raw fuel in the exhaust system when you can't get the engine to start and you keep cranking and priming the engine. when that happens and you finally get the engine to fire then all the fuel that has accumulated in the exhaust lights off damaging the muffler and other exhaust components. Just for clarification, I am not saying that cranking and pumping itself will do this. usually there are other factors making the engine hard to start and the act of cranking excessively can push fuel thru the engine and into the exhaust system.

 

Brian

[Hank]

Not that it gets super cold here, but you guys go up to 4-6 pumps in lower temps?

Sure do. Had to crank up around freezing for the Morganton, NC event. Forgot and only gave it two pumps, like to never started. Four pumps works better, then I wind & set the clock and put on my headset before cranking, because fuel vaporizes slower at lower temps. Yes, I had my oil sump heater plugged in, but also forgot to turn the prop 2-3 revolutions before getting in. Flying in the South is so much nicer!

[N33GG]

Used to have a Cherokee with a primer and never used it. Just pumped the throttle a couple of times when warm, and 4-6 when cold. Always started great. THEN...because I never used the primer, its seals dried out and created other problems and had to be repaired. Now when I have an aircraft with a primer, I occasionally use it, just to keep it working properly.

FWIW...

[carusoam]

The plumbing on an O360 puts the fuel line in at the top of the Cyl, compared to at the bottom of the intake tubes...

It makes a touch more sense. The cost and weight keep it from being highly adopted.

Preheating the whole engine makes the most sense.

At least preheating the intake tubes on the really cold days.

As OAT approaches 20°F, the evaporation rate of 100LL gets lower and lower. Pump counts can go above 10 or so...fuel is draining everywhere. Fire becomes a larger possibility.

From my PP experience of my M20C....

Best regards,

-a-

[orionflt]

anthony,

if your pumping the throttle 10+ times then yes you will have fuel coming out, the reason the engine needs an extra couple of pumps when everything is cold is because the air is denser and you need more fuel to get the correct fuel air mix, when its hot you need less fuel to get the proper mix.

 

Pumping 10+ is a little excessive and would require you to do a flooded start. 

 

Brian

[piperpainter]

If it's real cold I'd make that more like 5-6 pumps! 

[Andy95W]

If you pump while cranking you could run the risk of going to 1500 + rpm when the engine is cold- not something I'd want to do. With that said, you may actually have to do that if the weather is cold enough outside or the engine isn't preheated.

[ryoder]

My flight school which was also a maintenance shop told me not to use the primer and to pump twice.

[xrs135]

Good info on here. Sounds like I'm sticking to the book procedure, which has been working great for me so far!