Engine snag

[JAB]

Got a good one for the snag list.
During flat engine cut back to 2700 rpm max and ran rough. Left hand mag drop of 200 ish right ok.

Have tried the following:

Mags overhaul carried out, plugs and leads ditto. P leads and earths checked, mags switches replaced, mag adaptor replaced, mechanical check of engine ok. Fuel injection system ditto.
Egr shows 3000 static rpm with all t&ps as per norm. Despite having sought advice from many in the know, i am still getting a 200 mag drop on left

Any clues will be accepted

Cheers

JAB

[Neil Spooner]

What magnetos are you using?
Have you disconnected each plug lead in turn with the engine running to note the rpm drop on each cyl'?
What rpm drop at say 1000rpm?
Ditto 2000rpm?
If you can find which cyl' is the problem try moving the leads and see if the problem moves to another cyl.
Have you replaced the HT (distributer) caps on the mags?
Neil

[JAB]

Thanks Neil

My mags are Dual Bendix 3000 series.
I have had them overhauled with no futher progress.
Yesterday, and after much pondering by a Bendix experienced engineer, we suspect that the left coil is breaking down under load and as such giving a poor flow to the plugs.
I have just e mailed the engineers who carried out the overhaul and am awaiting with baited breath.
I am rather reluctant to strip the mags in order to carry out resistance checks as I believe that the overhaulers need the address this problem.
Was going to Wanafly in France this weekend but sadly had to bug out.

rgds

John

[Neil Spooner]

Hi John,
You know the saying....."time to spare....go by air"!
Those mag's make very good boat anchors!!
Good luck, if you have paid to have them overhauled then you should be looking to them to put them right I guess, if they were checked and overhauled properly then they should work up until the next due overhaul period. I did have one of these, but have sold it I think.
Regards
Neil