EGT increased running LOP

[G-SLOT]

While flying to Holland to bring @Hyett6420 back from delivering G-OBAL for its avionics refit, I perceived a slight roughness during climb to 9k (full throttle, 2500RPM, ROP) and then I could not get the engine to run smoothly LOP. Noticeable roughness beyond about 10 degrees LOP whereas normally she is very smooth deep into LOP territory. Was fine on the flight before. No sense of reduced power during takeoff but I did get the sense the CHTs were slightly warmer than usual (though perhaps because it was an unusually warm day and I was ROP (tried to keep it around 100 ROP WOT at 9k).

Luckily I was heading to the right place (Aeroskill, who have all of my logbooks, etc on site) and the excellent chaps there got the plane into the hangar and had the cowls off very quickly to investigate. They felt the sparks were looking a bit old so we replaced the magneto driven sparks but had to order new fine wires specific to the Electroair EI system for installation next visit. Tested the existing fine wires before reinstalling. Did a test flight with the mechanic who thought it was fine but, on the way back to the UK with @Hyett6420, we perceived some roughness too. Definitely unusual for my engine.

We did LOP mag checks and got the expected EGT rises on all cylinders when shutting off each ignition system but ended up running ROP most of the way home at 10k. Interestingly, down low at lower power, she was smoother LOP.

The fact that the engine was smooth on one flight and less smooth on the next makes me think there is some single issue, though I'm at a bit of a loss.

Plan is to leave the plane for its annual inspection (slightly earlier than planned) at Aeroskill when I take @Hyett6420 back to collect G-OBAL and have them go through everything - induction, exhaust, injectors, etc, on top of replacing the remaining spark plugs. 

Hopefully we'll find the issue but interested in any other things we.might check that could cause a sudden change of this sort.

[G-SLOT]

I don't have the special cable to get the data. Held off buying it given plans to upgrade to an 830 or 930.

[carusoam]

The data is everything...

If you could feel it, there is a foot print in there...

High EGT during LOP?

Sounds similar to a week spark not initiated the full burn... leaving a fire still burning after the exhaust valve...

That should be pretty easy to see in the EGt data...

Other issues become more obvious during the run-up, and the inflight mag check... if done slowly enough to collect good data....

We haven’t reviewed a good good set of data around here in a while...

How much for the cable...?   It might be worth it...

Best regards,

-a-