Hard Starting 912

[Morph]

I have noticed that over the last few mornings my 912 struggles to start, you have to crank it like crazy and eventually after the 4th or 5th time she will start. However beyond this you can give up.

I thought, since I have a tractor config in a closed cowling that after a long flight the heat of the engine compartment evaporates the fuel in the float bowl. So the next time you come and fly it is dry, but surely a few cranks of the motor should fill the bowls again

Maybe I should put an electric pump in and prime the carbs before starting?

[Tailspin]

Morph

Yea try to fill the bowls first.

It could be that she is not getting fuel immediately.

[Low Level]

Even if it is a 914, it is basically the same. I was taught by Gideon - Rotec - to crank my engine at least 30 seconds with the mags off before I start, to get the oil flowing. In summer I tend not to use the choke, but then battled to start the engine.

Now what I found, even if it ambient temp is quite high, first start of the day, if I crank with the choke open, and then put the mags on, she starts first turn, with the choke on. After starting I close the choke immediately.

If the engine is warm, I have no problems, and do not use the choke.

[CAROL]

Maybe I should put an electric pump in and prime the carbs before starting?


Yes, I did it with mine and it solved the problem

[Morph]

I have one, will do so this weekend

[Stephan van Tonder]

first start in the morning - mags off - choke on - electric pump till positive fuel pressure - electric pump off - crank till 3 bar oil pressure - choke off - mags on, crank - fires normally quite easily - ease throttle open till 2000 rpm.
Hot start - mags off - run electric pump till positive fuel pressure shows. pump off - crank till positive oil pressure. Mags on - normally starts after a couple of turns - might help to crack the throttle a bit.

IF you have the situation where it looks like the engine is kicking back against compression and the prop is flicking around and she refuses to start you might have excessive gearbox play. Only option then is a gearbox rebuild.

[Mogas]

My 912S start procedure:
Electric fuel pump to fill the bowls, only required if I have not started it for more than about 2 weeks.
Choke every 1st start of the day, summer or winter.
I crack the throttle open a tad for all starts, choke on or off.
I never crank it with the mags off, on my motor it is pointless as she will always fire after less than a full rotation of the prop.
Get the oil pressure up before firing? Yes that will do it but remember that you are drawing in mixture that will not be ignited, wetting the cylinder walls and washing off the thin film of oil that needs to be there.
I find that the rise in oil pressure after start on the 912 is virtually instant anyway.
Then immediately after firing I watch the oil pressure rise while establishing 2000 RPM. After about 30 seconds I will raise the RPM to 2500 till I get an oil temperature of 50C. Only then will I do the run-up to check for the mag drop.
Just to note Morph, the only time I have had hard starting on mine was when the battery was on its way out, ofcourse this started developing gradually. Problem was solved when I put in the new battery. I think the motor must turn fairly fast for this ignition system to generate a viable spark.

[Low Level]

I never crank it with the mags off, on my motor it is pointless as she will always fire after less than a full rotation of the prop.
Get the oil pressure up before firing? Yes that will do it but remember that you are drawing in mixture that will not be ignited, wetting the cylinder walls and washing off the thin film of oil that needs to be there.
I find that the rise in oil pressure after start on the 912 is virtually instant anyway.

True about the oil on the cylinder walls, but then when cranking, the heat and stresses on the rings is not really there yet. When my engine was opened up, Gideon showed me the difference between rockers where the engine was always cranked, and rockers where it wasn't cranked - quite a wear difference. Although the pressure shows, it takes some time - seconds - before full lubrication to the cylinder head. Apparantly that is where the problems come in. The cranking is to get full lube to the cylinder heads, especially after it was standing for a while.

I've noticed the difference in time for my oil pressure to rise is inversly proporsional to the time I have cranked the engine.

Just to note Morph, the only time I have had hard starting on mine was when the battery was on its way out, ofcourse this started developing gradually. Problem was solved when I put in the new battery. I think the motor must turn fairly fast for this ignition system to generate a viable spark.

Yip - had the same problem while training. The engine turns fast, but doesn't start. I thought there was problems. When I jumped it from another gyro - starts first turn. Thought it was weird - changed the battery - problem solved.

[Morph]

got a brand new battery. But I will check the voltage next time before starting

[John Young]

Hi,

Have chatted to Morph. Also had two occasions of hard starting.

Many opinions around. However, what is the advocated starting procedure according to Rotax.

A "touch of throttle" can effectively bypass the choke or enricher. My cruise throttle in any event has an inhibitor switch leaving me reliant on my right foot.

Plug gaps of 0.7mm to 0.8mm sounds excessive - but that's in the Rotax manual.

Looking forward to more opinions.

Kind regards
John ZU-sEXY

[Stephan van Tonder]

Can't copy out of the rotax operators manual document but it basically says - switch the fuel and the mags on and crank it to start. Not for longer than 10 seconds at a time with a 2 minute gap in between and put the choke on when cold.

but it's here http://www.rotax-aircraft-engines.com/p ... d02592.pdf

[tandemtod1]

Haven't seen in the Rotax manual where it refers to "choke" to start a 912 but rather they refer to the starting carburettor. The reason for this is that the Bing used on the 912 is actually 2 carburettors in one housing. One carb for starting and one carb for running. If you stick to the Rotax cold start procedure, it will start cold almost instantly every time. If it doesn't, then you have a problem which needs attending to. Noteworthy is as previously mentioned by someone else is that if you open the throttle beyond a crack during a cold start, the open throttle will render the starting carb section inoperative and the engine definitely will not start.
Most common causes for a difficult cold start:
Engine not cranking fast enough - check battery
Starting carb (choke) cables and mechanism sticking before they reach full open - clean and lubricate as required.
Starting carb jets (small jet located in bottom of float chamber) blocked with dirt/water/or grown some fungus from the fuel - clean as required
Hope this helps

[bluesmancoops]

I have one, will do so this weekend

are you not doing Stellenbosch this weekend?

[Ian]

Also have 912s inside a cowl, used to battle to hot start, now I have a process that works for me.

1. Switch on electric pump
2. Open throttle all the way - (dont know why on a butterfly valve carb this makes any difference but it does ) - wait 5 secs
3. Close throttle, switch off fuel pump when pressure up - start

Starts first time every time when hot now....

Cheers ian

[Trikenut]

Is the Fuel pump you tallk about a special one for priming or just a normal back-up one. (Like the ones so many guys have fiited just in case?)
If not, them what do you do WITHOUT the pump?