Can C/G owners tell me about priming/pumping during start?

[Heloman]

My airplane wont start, I'm not extremely familiar with "what's normal" because I just bought this airplane, on my third flight with my instructor it wouldn't start. Before this, it's started normally and ran well. I read some old posts where people have described that during their starting procedure they turn on the boost pump, build pressure, turn off the boost pump and then pump the throttle while watching the pressure gauge go down with each pump. My airplane does not do that, pressure builds on the gauge with the boost pump, I turn it off, the gauge stays at 6psi, I pump the throttle, the pressure does not reduce any faster then if I weren't pumping at all- it goes down very slowly. With this in mind, I started to suspect the accelerator pump might not be working, so I intentionally tried to flood it; I pumped many, many times, with pressure on the gauge, I've not got a drip of fuel out of the air box drain. I also pumped the throttle arm directly on the carb just to be sure, still no drips out of the air box drain. No smell of fuel, fuel selector is not off. Am I missing anything? Thank you!

[par]

You will receive a flood of replies on the "correct" starting procedure for a C and in the end, you will need to find one that works for you. Here is what I do in my C.

 

-Turn prop about 4 times by hand during preflight

-Master and Pump on as I jump into the cockpit.

-Check that there is pressure and then secure the pump

-Mixture full rich and pump throttle 2-3 times during the summer, 4+ times in the winter and set throttle about a 1/4" in

-Give the fuel about a minute to evaporate.

-Crank away

 

This usually starts my engine within a couple blade turns. On the rare occasion that it has taken longer, my battery just did not have a full charge or it was colder than normal and I simply failed to pump the throttle enough times. However, and be very careful with this, do not get to crazy with pumping the throttle. When all is working properly, you will flood the air box and the potential for a fire does exist. I had a very scary moment last year when I was new to my plane on a very cold day when it would not start. If you are pumping the throttle, you better be cranking at the same time. Keep cranking the engine at least for a few seconds after you stop pumping the throttle. 

 

My guess is there is something up with your carb/throttle/fuel system if you are not able to flood the air box. Hopefully others will have a better answer for you here but as far the starting procedure goes, that is what I use.

 

Par

[Hank]

par's procedure works for me, but I only pull the prop through a couple of revolutions in the winter. Or I did in WV, it ain't been that cold here in LA yet.

Master on, Fuel Pump on until pressure stabilizes, then off.

Mixture rich, pump Throttle. Fuel pressure should fall some with each pump. Twice in warm weather, more as temps fall, nine for a hot start.

give the fuel time to vaporize. This is when I out on my headset. In winter weather, give the fuel a solid 60 seconds to vaporize. Wind and set the clock. Now open the throttle 1/4-1/2" and turn / push the key.

are you getting any attempts to start? Coughs? Spits? Or just endless cranking?

[DXB]

Hi Heloman.  As far as general starting procedure, you post is giving me a flashback to last winter when I first got my plane.  The responses to my post within the thread below were pretty helpful- you may want to review.  Par is on the right track above.   But I find nothing beats having a heater on the engine the night before- starts instantly no matter what.  I've never looked at the fuel pressure while I've pumped- I'll have to watch next time.   I'm sure the real experts here will to weigh in on it though- I'm curious myself.

 

[carusoam]

My cold weather C procedure included 10 pumps. Fuel would be pouring out of it. (Fire hazard)

This was with no pre-heat available.  It worked on days above 20°F.

Three pumps for a warm day.

If you have gone 10 pumps, and then gone out to cowling and then don't see or smell fuel everywhere something related to the accelerator pump is not working. Electric Fuel pump, mixture, accelerator pump.

If your electric pump is making and holding pressure that's a good sign.

Get a copy of the Marvell Schebler carb drawing to see how the controls attach. Compare drawing to actual carburetor.  You should be able to find enough detail of how the two fuel nozzles, carb float and accelerator pump are operated. There could be seals or adjustments that need attention. Check the log for any OH entries or carb specific maintenance.

Each pump of the throttle gives a squirt of fuel.

Ideas that come to mind. Know that I am only a PP, not a mechanic. I stayed at a holiday inn while I owned an M20C...

Best regards,

-a-

 

[Jim Peace]

When were your mags last inspected and how old are the plugs?

Mine has started every time with:

During preflight NO turning of the prop.

Just before engine start fuel pump on and two full pumps.

Fuel pump off and throttle 1/4 open.

Engine start and check oil press.  

Works every time.

[Andy95W]

 

12 minutes ago, Jim Peace said:

When were your mags last inspected and how old are the plugs?

Mine has started every time with:

During preflight NO turning of the prop.

Just before engine start fuel pump on and two full pumps.

Fuel pump off and throttle 1/4 open.

Engine start and check oil press.  

Works every time.

I'm 95% with Jim.  I use 1 pump in the summer, 2 in the winter.  Open the throttle 1/8"-14".  If it doesn't start in the winter, I pump 2 more times while cranking.

No waiting.  No turning of the prop during preflight.  Pulling the throttle all the way out acts a little like a choke on an old car.

I've owned 2 M20Cs and both were the same.

Preheating in the winter is very important to get the fuel to evaporate.

P.S. Edit:  10 PUMPS to start an O-360 ?!?!?!  Holy crap!

[Wildhorsesracing]

5 hours ago, N1395W said:

 

I'm 95% with Jim.  I use 1 pump in the summer, 2 in the winter.  Open the throttle 1/8"-14".  If it doesn't start in the winter, I pump 2 more times while cranking.

No waiting.  No turning of the prop during preflight.  Pulling the throttle all the way out acts a little like a choke on an old car.

I've owned 2 M20Cs and both were the same.

Preheating in the winter is very important to get the fuel to evaporate.

P.S. Edit:  10 PUMPS to start an O-360 ?!?!?!  Holy crap!

That's my routine - any more than 2 pumps and I have fuel pouring out.

I keep my battery on a battery tender, without a full battery my shower of sparks doesn't have enough juice to make starting easy/smooth.

[Shadrach]

To those of you who are prop turners, can you expound on why you turn the prop? Everyone who uses this method appears to be turning the prop before priming, so it's not helping to distribute fuel. What does it do and why do you do it? I've flown a lot of carbureted airplanes, but I've never been told to do this.

[BDPetersen]

If there is no evidence of fuel after pumping 10x, something is not right with accelerator pump.

[JaredDavis]

WAG: Does it start when you release the key?

http://www.donmaxwell.com/publications/MAPA_TEXT/Shower%20of%20Sparks/Shower%20of%20Sparks.htm

 

[Wildhorsesracing]

1 hour ago, JaredDavis said:

WAG: Does it start when you release the key?

http://www.donmaxwell.com/publications/MAPA_TEXT/Shower%20of%20Sparks/Shower%20of%20Sparks.htm

 

That's some good info...

 

BTW - don't google "starter vibrator" - not gonna get what you think 

[Shadrach]

12 minutes ago, Wildhorsesracing said:

That's some good info...

 

BTW - don't google "starter vibrator" - not gonna get what you think 

For the beginner and first time buyer who's unsure about her...

[BigTex]

The O-360 engine is extremely easy to start compared to its IO brother. I turn boost pump on until 6 PSI is reached then off. Pump twice with a slight drop in fuel pressure each time. Then crack the throttle and crank. If your engine doesn't start in the first couple of turns, somethings not right. Check mags, plugs and carb. I'd personally not fly the plane until I figure it out.

Sent from my iPad using Tapatalk

[par]

2 hours ago, Shadrach said:

To those of you who are prop turners, can you expound on why you turn the prop? Everyone who uses this method appears to be turning the prop before priming, so it's not helping to distribute fuel. What does it do and why do you do it? I've flown a lot of carbureted airplanes, but I've never been told to do this.

The reason why it helps to give the prop some turns is to break the stiction. Additionally, I keep a couple of 100 watt light bulbs in the cowl flaps with a blanket over the cowling on 24/7 during the winter time. This keeps the oil temperature right around 50 degrees even on the coldest of days here in virginia. Turning the prop by hand will loosen up the engine somewhat if it has been sitting idle between flights and make life a little easier on the starter. This certainly is not a requirement but after my airbox fire experience last winter, I don't take any chances. I don't want to change something that works.

 

Par

[jetdriven]

How does turning the prop before priming have anything to do with lessening the chance of an airbox fire? 

I wonder if pumping the throttle just after hitting the starter would do both some good.  No flooded airbox and no grinding on the starter ?

[par]

6 minutes ago, jetdriven said:

How does turning the prop before priming have anything to do with lessening the chance of an airbox fire? 

I wonder if pumping the throttle just after hitting the starter would do both some good.  No flooded airbox and no grinding on the starter ?

It doesn't. Breaking the stiction makes life easier on the starter and reduces the chance of cranking for a longer time period. All these things pevent me from having to pump the throttle as the engine cranks, thereby reducing the likelihood off fuel gathering in the airbox and reducing the potential of a fire. Only in cold temps am I religious about this.

[Wakeup]

I am a newbie and was never taught  to  turn the prop, wait for the fuel to vaporize or to turn off fuel pump before starting?  My startup is mostly like Jims on my B.  Luckily, it starts up easily eveytime.  I'm crossing my fingers afters writing this.  

Troy 

[carusoam]

Andy,

I updated a line in there... This was with no pre-heat available.  It worked on days above 20°F. When fuel doesn't evaporate, it is hard to 'flood' the engine. Pouring excess fuel on the ground is a set up for a dangerous situation. The front tire gets bathed in the excess.

My C was parked outside in NJ with only expensive (non-CB) pre-heat available.  Flooding the carburetor while pumping is possible, just not neccesary.

It was a challenge to be young, not have enough money, and not have MS! Old wive's tales had to be spread face to face.

Back to the OP's challenge. Follow the documented procedure. If fuel pressure doesn't drop related to pumping, that's a sign.  If pumping a bunch of times doesn't cover the front tire with fuel that's another sign.  If the tire is dry, but it smells a lot like fuel, that's a different sign.  The drain hose might be missing and is now filling up the cowling.

 

Best regards,

-a-

 

 

[rbridges]

here's another "how I do it" answer.

boost pump on for a second or two.  2 pumps with throttle then pull back ~1/8-1/4".  crank engine.  once it catches, lean for taxiing.

[DanM20C]

Sounds like your accelerator pump isn't working.  You should have seen and smelled fuel with 10+ pumps. 

I find the O-360's to to very forgiving in regards to starting procedures.  0, 1, 2, 5, pumps etc.. Temperature does play a big roll in how much fuel you need.  In the summer mine will start in 2 or 3 blades with no pumps of the throttle.  I usually use 1 or 2 pumps and it starts immediately.  When it's cold out I usually start with 4 pumps and then be ready to pump one or two times after it fires.  I have tried waiting the 30-60 seconds for the fuel to vaporize but haven't noticed a big difference either way.  20 years ago when I was a private student I witnessed two fires at start up in the winter.  Both times it was newer students who were really slow with running checklists.  A min or so went buy from Priming (over primed?) to hitting the starter, giving plenty of time for the fuel to drain back down out of the carb.  After that the school started teaching priming just before hitting the starter.  I think induction fires are fairly common though, most of the time no one ever notices.

Never under estimate the importance of a good spark.  Tired mags will make starting more difficult too. 

 

Dan

[Shadrach]

46 minutes ago, par said:

It doesn't. Breaking the stiction makes life easier on the starter and reduces the chance of cranking for a longer time period. All these things pevent me from having to pump the throttle as the engine cranks, thereby reducing the likelihood off fuel gathering in the airbox and reducing the potential of a fire. Only in cold temps am I religious about this.

 Par, I'm sorry, but this is down right funny. While I don't deny the existence of static friction, the idea that you are saving wear and tear on your starter by turning the prop by hand is wishful thinking at best. How does it reduce the chance of cranking for a longer time.  If indeed there was significantly more static friction from the engine being at rest over time, one would merely need to bump the prop an inch, not turn it through 4 times.  I do preheat religiously below 40 degrees, but I'll let my starter take care of the stiction.

[par]

18 minutes ago, Shadrach said:

 Par, I'm sorry, but this is down right funny. While I don't deny the existence of static friction, the idea that you are saving wear and tear on your starter by turning the prop by hand is wishful thinking at best. How does it reduce the chance of cranking for a longer time.  If indeed there was significantly more static friction from the engine being at rest over time, one would merely need to bump the prop an inch, not turn it through 4 times.  I do preheat religiously below 40 degrees, but I'll let my starter take care of the stiction.

Wear and tear is not the concern. I'm just trying to make it easier for the prop to turn. Call it a myth but I'm going to keep doing what has worked 100% of the time.

[Heloman]

Thank you to everyone for the responses; I'm going to check the ignition system as well but it sure seems I have a fuel problem. It sure is frustrating working on other people's airplanes when yours has a problem and you don't have time to deal with it! Does anyone know where the fuel pressure sensor is located, is it possible to read fuel pressure without fuel reaching the carb? I have the maintenance manual but I've been having a hard time getting a parts manual from the two MSCs I've asked.

[Shadrach]

32 minutes ago, par said:

Wear and tear is not the concern. I'm just trying to make it easier for the prop to turn. Call it a myth but I'm going to keep doing what has worked 100% of the time.

If it works, it works. I think it's more leftover from the days of radial engines and the SOP of turning them through to ensure no cylinders were hydrolocked.

I like your avatar. Is that you? When was it shot?