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 rich:confused:Should 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:ugh:

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]

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. :eek:

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. :ok:

[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 :ok:

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 :ouch:

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]

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.

[stevef]

Easy when you know how. :)
I've heard some horror stories about running the battery down in the middle of nowhere because a hot injected engine wouldn't start. Someone told me he was once reduced to throwing a bucket of water over the engine to cool it down...

[homeguard]

Well, that would have done the engine a lot of good, wouldn't it!

[BIRK]

Just wait till you start flying aircraft with fuel-injected engines: It is some kind of a black art: many have tried, few have mastered. Sometimes it just seems that moving the throttle/mixture in some random order works best :rolleyes:

[modelman]

I can't understand why they don't start as easily as car engines,they are very similar in many ways,must be mainly down to having mags.Pity they don't have coil ignition just for starting.
You don't have to think about different techniques for starting different brands of car.

MM

[IO540]

If an engine doesn't start using the POH procedure, get it serviced!

The fuel servo may be knackered and needs an overhaul.

For example, my engine - while starting as per the book every time - used to really shudder on shutdown. Nobody thought it was abnormal. However, when it recently went to the USA for the SB569 crank swap, the firm noticed this and said it wasn't right, and they found a leak in some fuel control valve in the fuel servo; it wasn't closing properly and some fuel was getting through, preventing a clean shutdown. Now it's fine. But nobody in the UK would have noticed this.

That fuel servo would not have been looked at until overhaul @ 2000hrs which for most private pilots is "never". And even then I doubt the usual UK engine shop would have noticed anything.

The thing which also helps hugely is the installation of the new Skytec lightweight starter. I got the latest NL model (http://www.skytecair.com/Lycoming.htm) fitted. This is a lot more efficient because the permanent magnet has been replaced with a wound magnet; it rotates the engine several times faster than the stock starter, making cold starts instant and hot starts sorted within 2-3 seconds.

[Piper.Classique]

None of you guys have to swing the prop, do you? Believe me, if you do you soon learn what your engine needs. Arms wear out much faster than starter motors.....
We did have an interesting one on our cub. 150 horse lyc, with a starter motor. Zero time engine and mags, got progressively harder to start, hot or cold. Found out it was the spark generator for the shower of sparks mags that was dying. Apparently this isn't considered part of the :mad: engine.

The engine would actually start, which was probably some sort of miracle.

After several hours scrabbling around at the back of the firewall managed to replace the buzzer (which still _sounded_ like it was doing its stuff). Now we are back to starting on second blade.

For interest.....
Cold start pull the prop through 12 blades
Four strokes of primer
pull through 12 more blades
get in
mixture rich
switch on power to starter motor ( the separate switch is to allow a hand swing with the shower of sparks mags)
pump throttle twice then closed
both mags on (on key)
engage starter motor
when the engine fires gently advance throttle
check oil pressure etc....

Hot start
mixture rich
switch on power to starter motor
Pump throttle twice
throttle closed
mags on both
engage starter motor

etc....

The same engine in other aircraft usually has impulse mags, which are cheaper and easier to find. Most 150 cubs have no primer, and all the priming is on the throttle, with the mags on switches. We have a lot of little configuration oddities, probably due to the aircraft being a conversion from a 135, done in holland by the navy.:)

Used to fly a taylorcraft which would regularly catch fire on start. The prop swinger would wear a cap for this reason, which nicely covered the air intake to starve the flames. Saved filling the enging with gunge from an extinguisher. Interesting aircraft, combined all the worst points of the auster and the cub and none of their good points, but it was cheap to hire, which helped pay for the wear and tear on headgear. Still, at least the designer was capable of learning from his mistakes:D

[A and C]

I have had reliability issues with light weight starters, I doubt that this will be a problem that you will have due to the low engine start to engine hours ratio that you run as a private owner.

However those of you that have more than one engine start per 45 min of engine time may well want to think very hard before fitting a light weight starter.

[IO540]

True A&C, my 1st one burnt out after 2 weeks. Mind you, it was (not a Skytec) a 2001 stock which had never seen a drop of oil. It was an AOG job and I got ripped off £1000 - the real price is about $450.

The Skytec starters come in different versions. The original 'lightweight' one draws a huge current - see that URL I posted. The NL version draws much less.

[S-Works]

On mine..... IO360KB

Mixture rich, throttle 1/4" electric fuel pump to prime until pressure shown. Start. Same hot or cold.

[homeguard]

Going back to the simple normally aspirated systems.

When using the primer should the cylinder be flooded the fuel will run back into the hot air box just as it may using the throttle to prime.

There is no difference in that respect therefore whether OVERPRIMING using the throttle or the primer. Undertaken properly it is his view and mine that priming is best done using the accelerator pump which leads to better starts and is least likely to flood a cylinder. Most racing motor engineers i've spoken to hate the idea of neat fuel being sprayed into cylinders. Cylinder wash being the main concern. Also with a hot engine an exhaust fire is more likely even with light priming when using the primer.

[bjornhall]

Just wait till you start flying aircraft with fuel-injected engines: It is some kind of a black art: many have tried, few have mastered. Sometimes it just seems that moving the throttle/mixture in some random order works best

Now that is funny... I train largely on fuel-injected engines (C172R/S w/ IO-360), and have never had any problem at all starting them... See lots of people crank them 'til they're blue tho'.

One thing could be when priming by the book; fuel pump on, then move mixture towards full rich until you get an indication on the fuel "flow" (=pressure) gauge, then mixture cut-off and fuel pump off. The amount of priming you get that way will depend on how fast you move the mixture. Mixture full rich, fuel pump on, indication on fuel flow gauge, wait one second, fuel pump off, mixture cut off; seems to work better and more consistently. No priming when hot; the worst that can happen if you underprime is that it won't fire at all, so then you just stop what you're doing, prime, and crank again, it will fire.

[ExSp33db1rd]

Now for something totally different ! How do you start a 1960 VW 1200 cc Beetle engine without impulse mags. as fitted to my Druine Turbulent ? and pls.don't say 'with difficulty' - I know that ! Squirting neat Avgas down the carb throat and pulling 8 blades sometimes works. I always achieve a start, but never really know what combination of choke and throttle worked that time. Thanks.

[S-Works]

Just wait till you start flying aircraft with fuel-injected engines: It is some kind of a black art: many have tried, few have mastered. Sometimes it just seems that moving the throttle/mixture in some random order works best

Mine is fuel injected and starts as I stated earlier. Starting FI engines is just the correct technique, found be reading the POH.

[athonite]

This is all getting very protracted. best advice is what 'fireflybob' said, start the engine as directed by the aircrafts POH, which is part of the C of A, if that repeatedly fails refer the matter back to the engineer, it could indicate an underlying problem!

[david viewing]

I agree that it's getting protracted, but at least part of that is because some POH's are remarkably silent on the issue. The PA-28-161 POH for instance says to prime if the engine won't start, but makes no reference as to how, or how much, to prime.

As I said earlier, I'm convinced that much of this problem stems from 'difficult' engines that engineers and / or owners fail to rectify. In practice in most cases the underlying machinery is capable of satisfactory starting without extremes of cranking and priming. It is the same owners who will end up paying for new starter motors or much worse and I suggest that it is short sighted not to deal with these issues when they arise.

[Put1992]

Frustrated:ugh:

Modelman, having flown some of the aircraft you have, I wouldn't be.

If you were in RT, then you should be incredibly happy! Any completed flight in that, is a success :ok: