Carburator Fire

[IFMU]

Won't gravity pull the fuel down from the intake valves to the airbox, wetting everything that it touches as it goes? And won't this vastly increase the surface area of the liquid fuel? Will this increase in surface area not help fuel vaporization?

-- IFMU

[A and C]

IFMU

Yes you have a point but most of the fuel will end up in the airbox.

Ask your self why the engine makers take such trouble to fit the primer nozzels as near to the inlet valves as they do? It is because they want to get the priming fuel into the cylinders not the airbox!, if they had wanted the fuel in the airbox they would have saved the money and told you to pump the throttle a few times before you start the engine (no comments from Robin owners please!).

[tescoapp]

A&C there was an old boy who was the last ditch effort when it came to starting engines who used to have a slightly different method to most.


He would have the throttle closed then prime as the engine turned over while saying in a loud yorkshire accent "start y'r bugger"


He was of the opinion that 95% of starting problems were due to over fueling instead of being under primed.

What would be the pit falls of pumping the primer while turning the engine over?

[A and C]

Have you three hands ?

The problem with pumping the primer wile turning the engine are twofold, first the you cant control the engine RPM when the engine starts as your hand is on the primer and the second is the engine will draw fuel from the primer system once it starts if you control the RPM and don't shut and lock the primer.

The only up side to what you have sugested is that it is much less likely to result in an intake fire than the practice that IFMU has advised.

I have a lot of time for the guy who said that over priming resulted in a lot of problems even if he was a yorkshireman!

[tescoapp]

It didn't seem to be a rushed thing.

first he would close the mixture and turn the engine over for 30secs.

then full mixture, zero throttle

Turn the engine while pumping primer.

Depending on type as soon as it fired he would either transfer the key hand to the throttle while locking the primer. Or finish the pump stroke locking it.

Then hand to the throttle.

The result was always the same engine ticking over at 600-700 with no over reving. And on the rare occasions it didn't work it was pulled into the hangar for the engineer to watch while he pulled the spark plugs and did things to it.

Another one of his phrases was "let the bugger be with all that noise, give it a couple of mins to get used to the idea its going flying"

[SNS3Guppy]

Clearly you don't understand the construction of your engine, If you pump the primer and then leave the aircraft all the fuel will run down into the airbox.

The practice of priming the engine and then doing the walk round inspection is just a good way of setting up your self for an intake fire.

That really depends on the position of the valves at the time, and which cylinders have been selected for the prime. It also depends on the engine, and the induction arrangement. Fuel may end up in the induction, exhaust, cylinder, or pooled in the cylinder head by the intake valves.

Bear in mind that with a cold engine during a cold weather start in the big radials, we filled the supercharger with avgas while cranking. I knew an old captain who used to say that unless you could get at least a five gallon bucket draining out the supercharger drain during the start, you weren't flooding it enough to get a reliable start. In a light airplane engine, starting off the mixture and adding fuel as you crank is probably a much better idea. Just rememeber lean when hot, rich when cold...and forget about the accelerator pump. Leave the throttle alone during the start.

[A and C]

Guppy

This is thread is about a Cessna 152 so talking big radials is irrelivent in this case.

The only reason for needing to touch the throttle on start is to control exessive RPM, I except that some fuel may get into the one cylinder but most of it will end up in the airbox if the engine is primed before the walk around is done.

[DX Wombat]

This is thread is about a Cessna 152 so talking big radials is irrelivent in this case.

That's a bit high and mighty A&C. This thread may be about starting a C152 and, whilst I haven't seen one with a radial engine fitted, surely any information on starting any engine is welcome? After all, not every C152 has the same make or type of engine fitted. As far as I am concerned, it isn't irrelevant at all, it's another snippet of information which may prove useful one day.

[SNS3Guppy]

This is thread is about a Cessna 152 so talking big radials is irrelivent in this case.

Got it. Perhaps you're slow enough you can't follow along, so we'll break it down for you, so that you can.

The only reason for needing to touch the throttle on start is to control exessive RPM, I except that some fuel may get into the one cylinder but most of it will end up in the airbox if the engine is primed before the walk around is done.

Once again, where the fuel goes depends on the position of the crankshaft, camshaft, lifters, pushrods, and valves in the Cessna 152; it may drain into the induction, it may drain into a cylinder, it may stay in the cylinder head, for that matter.

With the 0-235, a cold start is a wet start, whereas starting lean or dry in hot weather is the general norm. It also applies to radial engines.

On the subject of prime, for those who aren't aware, failure to lock your primer can lead to a fire, or an engine failure.

[llanfairpg]

Seems to a be a lit of engineers on here--funny how you can never find one on an airfield when you want one!

[DX Wombat]

Seems to a be a lit of engineers on here

But are they licenced or armchair?

funny how you can never find one on an airfield when you want one!

The engineers are one of the few species of (allegedly) human beings who have perfected the ultimate cloaking device. A bit like policemen etc.
Just joking

[A and C]

I was not meaning to be "high and mighty" as someone put it but all engines are not the same and the advice that is reqired will be different.

I see little point when some one is asking about starting a C152 in giving advice on a totaly different engine or going into so much detail that people are not giong to read past the first paragraph.

I have been trying to stay on topic.................... now on the Bristol sleave valve engines......................................

[LowNSlow]

or the Napier Sabre which had to be left alone until it dried out if it didn't fire after the first Koffman cartrdige was used....

Mags off, four strokes of the primer, pull through 5 blades quite quickly, mags on and pull the prop through the compression usually works for a cold Cirrus Minor II.