Engine starting problems

[modelman]

Engine starting problems
After going all through my training having no problems starting,I don't seem to be able to get instant starts sometimes these days.
On Saturday (quite a warm day),I used a 152 that had just flown and had stood for about 25 mins.I didn't prime,and the engine spun for what seemed ages (prob only about 10-15 sec) and staggered into life.Difficult to judge whether it was starved or richShould I have primed or not?

I have also had a problem with a PA28-140 on a cold day-can never seem to decide if I have overprimed or not.

Frustrated

MM

(originally posted on another thread doh!)

[IO540]

What does the handbook say about cold starts and warm starts?

Different engines have slightly different procedures.

[fireflybob]

Firstly read the POH and follow the correct starting procedures (and I mean the POH and not some fancy checklist that somebody else has produced!).

Be particular about setting the throttle, if the POH says 1/4 inch then thats what they mean!

Thats said, some basic advice for PA28 -140 - if the oil temp is in the green then do NOT prime, if its below the green then prime, how many pumps depends on OAT - on a cold winter morning maybe 4 or 5. When you withdraw the primer do so slowly (that way you suck up more fuel) and push in quickly (better atomisation of fuel).

If in doubt UNDER prime - then at least you know where you are starting from.

If the engine does not fire within a few seconds of engaging the starter then RELEASE the starter (often when you do this the engine fires and starts!). Wait a few seconds before another attempt. This gives the starter and battery a bit of a rest and quite often the engine will start on the second attempt. Do NOT just keep cranking assuming its going to start.

Hope this helps.

[smarthawke]

One problem which happens particularly in the O-235 in the C152 and PA38 is the starter spins the motor over fast enough to disengage the magneto impulse coupling but not quick enough for it to generate a big enough spark to start the engine.

When you release the key from 'start' it naturally goes to both (ie 'on'), as the motor slows down now that the starter isn't driving it, the impulse coupling engages and hey presto, the engine starts.

Various things were tried with the starter (to turn the motor over slower) and the magneto lag angle. of course if you mix and match mags and starters....!

Individual engines do behave differently and if you get one with a weak impulse coupling then you're on a hiding to nothing.

All part of the fun of flying (or trying to go flying)....!

[IFMU]

mm,

On our pawnees we had starting problems last season. Lots of speculation about the mixture being off, we tried starting with the mixture leaned, ect none of which made any difference. Turned out the mags were tired, and not making good spark at low rpm when the impulse coupling was active. New mags and we were good as new.

-- IFMU

[KingAir77]

Starting an engine seems sometimes to be an art for people new to their quirks and moods, depending on all sorts of environmental conditions. Having the POH say "prime as required" does not really help the novice either..

Consider what you have, hot engine or not, warm or cold outside, to come up with how much you prime. My experince shows that generally the Cessnas need a bit more priming, even a sizzling hot engine can do with a stroke of primer, whereas for some reason PA28s seem to drown in fuel if you only look at the primer. The 172 and the Pa28-161 share the same engine, but stil there must be differences in the intake or fuel system to explain these differences in behaviour.

Also read the POH, if your carburetor is fitted with an accelerator pump, you can use the throttle to "prime", I found this to be usefull on the PA28-161. Pump the throttle 5-6 times with the mixture in full rich, then it starts well (cold engine that is). The amount of fuel injected that way is less than what you would give it with the primer, and it seems to be doing the trick.

[homeguard]

Getting started

I also prefer to use the throttle (accelerator pump) to prime. Less likely to overprime.

Also, it is not uncommon that some priming systems only prime two or even only one cylinder. When this is the case the engine can be very difficult to start, particularly in cold weather and the engine can take some seconds of rough running before gaining proper rpm.

[OpenCirrus619]

I also prefer to use the throttle (accelerator pump) to prime. Less likely to overprime.

On many (if not most) aircraft engines this is potentially dangerous. If you use the accelerator pump in an up-draught carb, when the engine is not running, you risk fuel collecting in/around the air box / filter / intake - just waiting for a backfire to start and engine fire. The primer injects fuel into the manifold - where it is not going to run out.

I accept that, on many installations, either:

• Pumping the throttle is the only method of priming.
• The process of priming involves fuel ending up all over the ground (Gipsy engines).

IF there is a system designed to prime the engine, I can't help feel it is sensible to use it.

OC619

P.S. While on the topic:

Does everyone know the procedure, on their particular aircraft, to be followed in the case of a fire on startup - WITHOUT referring to the check list?
If not a little revision may be in order - if it happens you won't have time to look then.

[russellmounce]

I fly the PA-38, and always seem to have problems starting whether it's just flown or been sitting in the cold all week.

I'm always scared of over-priming. What will happen if I do prime too much?

[Put1992]

Hi Modelman

I know exactly what you mean, and i've found that it's due to lack of priming (even after something like 25 mins), and that the engine can sometimes use that little bit of encouragement from the throttle if it's feeling reluctant

I remember rick saying, first thing in the morning, 3-5 "primes", halfway through the day, 1-3.

In response to the fire on startup, without refering, with my hand already on the throttle, retard that, mixture to lean, master switch off, get out

Cheers

Put

[Captain Smithy]

I don't recall having any problems starting the engine (PA-38).

Usually my instructor recommends 5 primes cold, or 3 when warm. Seems to work fine for me. Suppose it will probably vary between different aircraft/engines, even of the same type - age/wear-and-tear etc.

Smithy

[OpenCirrus619]

First rule: Know whatever the POH indicates for the particular machine you are in.

Below is a generic approach - but, again, the procedure in the POH is what you should follow.

ENGINE FIRE ON START
Continue cranking to attempt to suck flames back into engine.
The best thing that can happen at this point is the engine starts - which means it will suck even harder. If it does start AND there are no further signs of fire then run it at 16-1800rpm for a couple of minutes, then shutdown and check for damage.

if it does not start:
Continue cranking it will still probably be sucking flames back into the engine.

after 15-20 seconds cranking OR if the fire appears to be growing:

• Mixture - ICO
• Fuel - OFF
• Ignition - OFF
• Master - OFF
• Vacate aircraft - Taking Fire Extinguisher (if to hand)

If fire is still in evidence AND you have a fire extinguisher in your hand: Discharge the entire contents into the engine bay and RUN - if it isn't out you can't do any more, if it is you've broken sweat for no reason.

You will see procedures that suggest calling for the fire service, on the radio, while cranking. IF your radio is on, and tuned to the tower, go for it - but most start procedures require the radio to be off before start. IF your radio is off DON'T start playing with it.

OC619

[First_Principal]

I see some comments on overpriming - I had an interesting experience a few months ago when an O-360 was overprimed (largely due to a faulty valve) several times over the course of a few weeks. On each occasion the engine hydrauliced on the intitial attempt at turnover and was subsequently turned over (slowly!) by hand to exhaust the excess fluid before starting properly.

The final straw was when the started motor broke - catastrophically - due to the excess and instantaneous load on it when it came up against the 'full' cylinder. The primer valve was replaced fairly soon after that.

In one sense this was a lucky event - the motor has done quite a few hours since and hasn't seemed to have suffered as it could have done. Had it continued and/or the motor fired on another pot before coming up to the full one it could have been very serious indeed! Even more serious would have been damage that showed some hours later - in the air - as could happen due to a bent rod etc.

Since this we have changed procedure to only prime the engine whilst turning it over - not prior to. This does mean a longer turnover before it fires so it's a bit harder on batteries and the starter, but it's safer, IMO, on several counts. The motor(s) are much less likely to hydraulic or to have excess fuel on start that could cause an engine fire and/or wear the bores (fuel will wash off the oil film on a cylinder wall thus greatly enhancing wear in the first few passes of the piston prior to firing and obtaining oil splash lubrication etc).

While in this instance the primer mechanism was electric as opposed to the hand plunger mechanism often employed it doesn't mean similar problems couldn't occur with this. They'd be much less likely (you'd have to pump quite a bit to hydraulic methinks) but one of the secondary issues I've mentioned could well occur over time... so I'd be an advocate of underpriming and putting up with a few more turns before the engine starts rather than overpriming and having the potential to cause damage through wear, plug fouling, fire, hydraulicing or whatever.

FP.

[Mike Cross]

One thing I've noticed on our C85 (which the O-200 was developed from) is that it does NOT like the throttle cracked when it is warm. This turns into a little game, It won't fire if the throttle is cracked but it won't fire well enough to keep going if it's closed so you end up cranking it with the throttle closed so you're getting some firing and then gradually ease the throttle open a fraction until it picks up. We have no accelerator pump so this doesn't stick extra fuel in.

The usual result of overpriming is that it won't fire at all with the throttle closed or open. Opening the throttle a little (say one third) while cranking with your hand on it ready to pull it back if it fires will often clear it.

If that fails a cup of tea (poured into the pilot, not the engine) usually does the trick.

[Superpilot]

OR if the fire appears to be growing

Now there's something you don't often read in an emergency checklist!

[david viewing]

I also prefer to use the throttle (accelerator pump) to prime. Less likely to overprime.

NOoooo.....!

Not on the PA-28-161, at least. A few years ago a renter pilot set the Warrior we were operating on fire during startup. It was only saved buy a nearby pilot who discharged his own extinguisher into the cowling.

After recovering the aircraft we carried out some tests. The pilot had mentioned priming by pumping the throttle and it turned out that four or five pumps of the throttle was enough to have neat fuel running out of the hot air valve under the carb. This assembly is far from sealed and so this fuel ran straight onto the inside of the cowling.

In contrast no reasonable amount of primer use would produce neat fuel running back through the inlet. Apparently the design of the inlet pools the fuel in the head rather than letting it run back.

What started the fire? Backfires are apparently very likely and that's all it would take. If the fuel is already in the engine bay, no amount of 'drawing it back in' etc will help. (edited to say I suppose if the hot air was selected then it might draw the flames in I suppose)

Behind all this in my opinion is the issue of poor starting which seems to be widely accepted and leads to pilots searching for 'innovative' techniques to get going. In my view poor starting is as serious a fault as, for instance, no radio or something like that and needs to be fixed rather than justified as seems to be the habit of some engineers of my former acquaintance.

There's no reason why the engine in a Warrior should not start immediately, hot or cold, and if the aircraft you fly doesn't do that then I suggest complaining until they find out what's really wrong with it rather than accepting the situation and risking, as also happened to the same aircraft, a burned-out starter motor in the Channel Islands, or something much worse!

[homeguard]

Prime Starting

On very many types, both old and new, you do not have a seperate primer from the throttle.

Using the accelerator pump is as often as not the only means to prime. When less than all cylinders are primed using the throttle also gives smoother and more positive starts. In thirty years I have never witnessed as described a fire due to priming using the throttle. I have witnessed many exhaust fires caused by overpriming using the dedicated primers. Plus of course many flat batteries following overpriming with a primer. That is flooding the engine together with a false believe that if you keep it turning the engine will fire. If the engine is warm it is very rare in my experience that you should need to prime, quite the opposite - consider leaning.

Improper and inappropiate priming is easy to avoid if care and thought is taken. Should the exhaust be hot enough to ignite waste fuel one should wonder why priming be consided in the first place.

[stevef]

Hmmm - I guess I've been lucky: in thirty years I've seen several fires caused by using the throttle (accelerator pump) on start up, the last one only a couple of months ago on a T67. Conversely, I've never seen an intake fire being induced by using the normal primer, where fitted. As a maintenance guy, I never use the (forced) throttle to start the engine, hot or cold, and haven't had a problem.
Injected engines do need another technique of course: the Lyc IO 540, for example, needs full throttle and idle cut-off to start when hot.

[barrow]

If the pa28 has a separate starter button, then start on left mag only, then to both.
lycs don't have accel pumps if under 110hp.
If your gonna prime with throttle, make sure the prop is spinning before pumping throttle.
Cold start on 152 or warm, push primer as engine turns,
crack throttle, mix full rich, key in right hand, push primer with left, keep priming till she fires.

[IO540]

the Lyc IO 540, for example, needs full throttle and idle cut-off to start when hot

On mine (TB20):

1. full throttle, mixture closed
2. boost pump for 1 sec
3. operate starter
4. when engine starts, mixture to full and (very quickly, to avoid high revs) bring back the throttle to idle

Works every time.