Morning Sickness

I have an IO-540 fitted to my -10 and have been having some minor issues first flight of the day.

Everything was fine until I was away from home for about 6 weeks so decided to install desiccator plugs. The problem started after I refitted the normal plugs although I have difficulty believing it has anything to do with that - just coincidence.

On the first flight, the engine starts fine but then starts to stumble. I don't believe it is an ignition fault as it dies and then recovers if I give it a bit of throttle. It's almost like a vapor lock but can't be. Putting the electric pump on makes no difference. There is no evidence of any water in the system. I also do not believe it is the traditional "Morning Sickness" of a sticky valve - the engine is only 25 hours old and it is definitely like a weak cut rather than a misfire. By the time I have done the engine run-up all is well. Second flight of the day, no problem.

The first time it happened, I put it down to the engine having sat there fore 6 weeks but it occurred again the next day, although not as bad. I haven't flown since as I am away and the engine is again inhibited. I am hoping to fly again in the next few days, so any ideas?

In summary:

- doesn't feel like an ignition problem
- doesn't feel like a sticky valve
- can't be the EDP as the electric pump ON makes no difference
- can't be vapor lock as the engine is cold

That leaves water. The drains are clear but I suppose it could be collecting somewhere else. The aircraft is kept in an unheated hangar so could it be condensation in the fuel? This is the first winter the aircraft has been finished and flying.

More than irritating as the engine had been running absolutely sweetly! Any thoughts appreciated.

Sounds like a mixture issue if anything.

Cold start, would like an enriched mixture like a choke but isn't getting it.

When warm - no longer needs it.

Check the throttle body linkage and make sure you are actually getting full rich on the mixture.

When it stumbles, try leaning out - if it stops instantly - weak mixture.

I'll have a look Mike, but don't think so. The engine starts fine, runs for about 10 seconds then starts to run down. Give it a bit of throttle and it picks up. Continues to do that to a lesser degree until the run up then all is well. I have very little experience with Pistons but the research I have done leads me to believe that there is some sort of interruption to the fuel. I've ruled out the EDP, can't be vapor lock so that seems to leave water - just can't work out where it is coming from. On the plus side, it would be the least worrying issue........

Mike Busch has some good recommendations on the best way to diagnose an engine problem.

• Ignition Stress Test
• Mixture Distribution Test
• Induction Leak Test

Details can be found here

What are the EGTs doing during this stumble?

You don't say how cold, cold is, but if you haven't adjusted the mixture (link on the servo) properly, for the outside temps, it can cause this type of stumble.

I doubt you have a sticky valve, very much doubt it.

mike newall said:

Sounds like a mixture issue if anything.

Cold start, would like an enriched mixture like a choke but isn't getting it.

When warm - no longer needs it.

Check the throttle body linkage and make sure you are actually getting full rich on the mixture.

When it stumbles, try leaning out - if it stops instantly - weak mixture.

Click to expand...

I'm with you Mike, mixture would be first thing to check. It sounds too lean for the lower temps, and is ok as the engine warms. A better description of the symptoms would help.

+1

BillL said:

I'm with you Mike, mixture would be first thing to check. It sounds too lean for the lower temps, and is ok as the engine warms. A better description of the symptoms would help.

Click to expand...

I agree with Bill, and others. Bennair; Dunnatt - with my 540s. Heck - even my Champ with an A-65! Fatten 'Er up a bit.

Good luck!

Carry on!
Mark

In retrospect, I am beginning to think that it may well be that the mixture is not going fully rich. I remember thinking, now, that the mixture control didn't seem to go as far in as I had recollected. It's entirely possible that when I replaced the cowls, the bottom one has seated in a slightly different position and is JUST interfering with the mixture arm - the clearance was pretty tight. That being the case, easy fix......

Just arrived back in UK and will check at the hangar tomorrow and report back.

Thanks for the advice - as I say, limited piston experience.....

Nice n number.

Post Engine Data

In case you use Savvyanalysis would you mind sharing the link of the engine data here. It helped me always to narrow down issues.

Mike

Well, it looks like Mike was right all along

I took the lower cowl off and found the mixture arm was about 1/4" or so off its stop. I then found I could move it that bit extra using the cockpit control. There were witness marks on the cowl - on the angle of the air intake section. A quick "re-profiling" with the Dremel and all now works as it should.

I have another couple of jobs to do before rolling her out and running the engine but I think the problem is solved. Thanks guys!

Great result and once again, shows the effectiveness of Doug's Forum

Just to close the thread - started up today and back to its normal, sweet self. I just wish all snags were so easy to fix. Well, easy when you have thousands of experts on VAF!

Thanks again, guys.