Missing a beat

[Fuji Abound]

I have noticed on the odd occasion the engine misses a beat!

To be more specific, on odd occasions there is a momentary hesitation in the engine. The engine continues to run fine, and there are no subsequent problems. I know this isn’t type specific because I have had it happen on a number of different engine types, both injected and not. I think I also know that it doesn’t appear to be indicative of a problem with the engine. The miss a beat syndrome is pretty uncommon, maybe once every 100 hours, but of course it always gets ones attention.

I wonder how often other people notice this, and what is the likely cause. I guess it could be a momentary contamination of a plug, or maybe a little moisture in the fuel, but I have never really been certain.

Have others had this experience and what are the likely causes.

[inbalance]

I ve noticed that a couple of times, but I ve got no Idea where it comes from.

[Flyin'Dutch']

Hi

Can of course be a multitude of matters.

However not unusual for a sticky valve to produce symptoms like this. All changes in engine behaviour can be early indicators of impedending trouble and as such warrant to be investigated.

FD

[Keef]

Mine does it evey time we leave the shores of the UK bound for abroad.

Or is it just that my ears get more sensitive then?

[rotorboater]

Isn't it funny how your heart misses a beat at the same time!;)

[Dude~]

Could be a small build up of carb ice melting and mucking up the mixture temporarily.

[Fuji Abound]

Flyin'Dutch'

"All changes in engine behaviour can be early indicators of impedending trouble and as such warrant to be investigated."

To take a specific example. The engine is injected, and recently zero timed. No problems found at the 50, which included a compression test and oil analysis. Are you suggesting that further investigative work should be undertaken and if so what?

How far would you go with further examination if the occurence was isolated, with no further problems with the engine.

[Flyin'Dutch']

FA,

In my opinion engines only miss a beat for a reason.

The engine in our Robin had a sticky valve (unbeknown to me) which led to a valvestem failure, piston damage and some excitement and grey hairs. It had 75 hours since overhaul at the time.

How far you investigate any abberant engine behaviour depends on how narrow or thick your comfort zone is.

Unlikely to be an ignition problem and obviously with the system being injected you can forget the carb ice theory!

HTH, but let me know if you want to have a further chat.

FD

Have a look here (http://www.equipped.com/1199ditch.htm) if you think that engine failures only happen in hight time aeroplanes and engines

[Tango Oscar]

Our group owned Robin regularly misses a beat. In fact, it misses a beat everytime in a certain senario i.e. when at a very low power setting, then increaseing it. It only has to be a slight increase, but every time, it misses a beat I'm sure it has only started doing this since it's come back from it's C of A renewal, but I'm quite new to the group, so I may be wrong. Anyone else experienced problems like this ?

[Mark 1]

TO,

Symptoms like that when changing power aren't uncommon.
The likely cause is lean cut or rich cut.
Lean cut is when the throttle is opened quickly, the amount of air entering the engine increases more quickly than the carburetter can supply more fuel, hence fuel/air ratio temporarily drops to an overlean state.

Rich cut can be where an accelerator pump in the carburetter supplies extra fuel to overcome the lean cut, but due to the rate of throttle increase it overdoes the correction.

The usual solution to either problem is to make your power changes more slowly.

[Tango Oscar]

Mark 1 - thanks for your comments.

Usually, the 'missed beat' happens when I'm on final, and just making a small alteration to keep on the correct glidescope, so the changes in power setting are both small and gentle. The problem also occurs when advancing to full throttle from low power settings. as happens when doing PFL's. At all other times, the engine runs very soothly. The engine was new 200hours ago.

T.O.

[A and C]

I had the engine in my Robin miss a beat the other day when in the cruse , when I went to push the throtle FWD a slight resistance was felt and it missed another beat.

I think that this was the engine reacting to the ice that I had disturbed by moving the throtle.

Carb ice may seem unlikely with the heatwave that we are having at the moment but I think that one should remember to use the carb heat as even with a big temp/dewpoint split the air contains a lot of water at these high temps.

[Shaggy Sheep Driver]

Our Chippy was 'not quite right' for a while after we fitted a new engine last year. It was much improved by applying the 'plug mod' which enables us to use more up to date plugs in the engine - but it still 'missed' occasionaly (notably on take off from G-VFWE this year, cuasing a land- back). Another symtom was 'juddering' of the engine when reducing power. It ran fine at high power, missed and juddered during the power reduction, then ran fine at the new power setting.

The engineers couldn't fathom it. The fault eventually went away when a mag was changed at a 50 hour check - becuase of rough running.

Fingers crossed, it seems OK now.

SSD