Menu Sign In Contact FAQ
Welcome to our forums

TB20 engine fire, due to too much priming

I have found that simply following the POH for my TB20 it starts every time. During cold weather I leave a few seconds more between going from idle cut off (ico) to turning the starter to allow the fuel to vapourise.

The hot start procedure isn’t pleasant as it calls to start with throttle fully open. First throttle full power, fuel pump on, mixture full rich for one second with fuel pump on then back to ico and fuel pump off. Then start the engine – remembering you have the throttle set to full power. It’s a lot of hand movement in a short time. I try to avoid a hot engine restart but sometimes it can’t be avoided.

I only ever put my seat belt on once the plane has started successfully without there being a fire.

I use the POH procedure too.

The tricky one is a “warm” start. I am not sure what is the best way, but I use the hot start. A fast starter definitely helps.

Shoreham EGKA, United Kingdom

Thank you for posting this. By being embarrassed and not posting, nobody else has a chance to learn. None of us are born knowing everything (none of us die knowing everything either!). All we can hope to do is learn from others (and our own mistakes) hopefully before we need that knowledge!
So thanks for sharing!

I second that!
Thanks @Rami1988

always learning
LO__, Austria

IME starting lots of different engines (carb, fuel injected, EFI), the root cause is usually the starter not turning the engine fast enough. Typically this happens in cold weather. The battery is way below peek power, and the oil is like sirup. Engine heating always work, and charging the battery sometimes work. Fuel needs heat to evaporate too, and if the engine is cold soaked, there’s not much heat to get. Turning the propeller slowly does not produce much compression heat either. The principles of EuroGAguest will work, but it’s not very easy to do alone with a hand propped Cub

The elephant is the circulation

AFAIK the fuel injected engine will always start “eventually” if you set up the normal idle settings on the throttle and mixture levers.

This will always be “safe”, and I’ve seen it used to do a “warm start”.

It might just take a while, and this is why the cold start and hot start procedures were developed.

Always look at Threads possibly related to this one below and in this case you find Injection Engine Start-up science.

The Q in this case is what should one inspect. How vulnerable is the fuel servo? There are four little tubes which sense the airflow. I would expect the fire to have been all through that region, because when you prime an engine, the fuel comes out in that very area. OTOH the servo ought to be designed to withstand that. Any ideas?

Shoreham EGKA, United Kingdom

Lucky for me there was no sign of any burning on the other side of the air filter. Only on the outside bit. The inside of the sponge is somehow spotless.

I guess this means no need to check the fuel servo?

Last Edited by Rami1988 at 14 May 11:56
EGKA, United Kingdom

So far I haven’t had hot-start problems with the TB20 – I haven’t flown it that much :-( but all through last summer I flew with no problems.

But I did once fly a fuel-injected 182 which suffered terribly from vapor lock and was a nightmare to hot start. I remember taking it to Santa Rosa, maybe 60 miles from Palto Alto, on a very hot day, and desperately trying every combination of idle mixture, full mixture, full throttle and all the rest. Just when I was beginning to see a rental car in my immediate future, I somehow hit on the right formula and it started. I had several other bad experiences, too.

Interestingly the mechanic who took care of it said there was no problem, it just took the right combination of lever movements, though I forget what his magic formula was.

Last Edited by johnh at 14 May 12:47
LFMD, France

eurogaguest1980 wrote:

Consider the classic lever dance. It’s really a sweep moving toward lean from a condition of way too rich. First we flood it (full rich, boost pump on), which ensures we’re beginning the sweep on the too-rich end. Then we put the mixture at ICO and the throttle wide open; when we start cranking, no more fuel is added, but we’re supplying plenty of air. With each intake stroke the fuel/air ratio presented to the spark plug becomes progressively leaner and leaner. When the ratio passes through the stoich range (or close to it), spark makes fire. We close the throttle and open the fuel (the lever dance), hoping to remain in the sweet spot.

While this works well most of the times for a hot injected engine start, it is very type-dependant.
Continentals are for whatever reason more prone to fuel vaporization than Lycos and after following the above dance you may find you need fuel boost pump on momentarily to quickly get those bubbles out of the system or else the engine will die again shortly after start. Since, unlike RSA injectors on Lycos, Contis also have a fuel return line, it also helps to circulate fuel with mixture closed before start since it cools down gascolator, fuel pump, mixture valve and lines . THis usually works, but when you try that at 5000ft elevation on a hot soaked engine 30 mins after landing, things can get difficult. Sometimes waiting 15 more minutes is all you need! Ask @Dan how I know!

LESB, Spain

Only on the outside bit.

That’s amazing I guess there wasn’t enough oxygen behind the air filter.

The standard advice for a fire like this is to keep cranking with the starter motor, as that supposedly sucks the fire into the engine where it doesn’t do harm.

Shoreham EGKA, United Kingdom

Exactly – I questioned the engineer a lot about how is there no sign of anything burning on the other side of the air filter he said there was simply not enough oxygen and you’re a lucky man!

Also did the 50 hour check (even though still on 40) as I hadn’t done any checks myself yet on this aircraft and turns out half the spark plugs are somewhat worn. Whilst routine, we dont know since when they are worn as we didnt do the last chefk, and that could also explain why it was harder to start the engine?

EGKA, United Kingdom
Sign in to add your message

Back to Top