B

beberle

Active Member
I hope someone's run across this before and can lend some advice..
seems like my full-rich EGTs have been slowly climbing for the last couple weeks. Really caught my attention on the last flight when full rich at 2300rpms @3,000 density altitude was showing 1400deg. That's what I usually lean to, peak EGT is usually around 1500.
The old full-rich baseline seemed to have been 1320s before in this setup. The EGTs are even across all 4 cylinders. Fuel pressure hasn't changed. Turning on the boost pump doesn't change EGT at all. My trusty VM1000 seems to be running great. And yes, the peak EGT still shows 1500s, just don't have to lean very much to get there.
My best guess is a possible air leak at the carb???
 
Definitely sounds like you're running leaner than before, or ignition timing is drifting. If your peak EGT is still the same and a leaning check tells you don't have to lean nearly as much as before to get to that peak, that smells like mixture changing rather than ignition. Time to pull the cowl and check seals.
 
You could have one massive induction leak, that is true, but lets look at a few other things.

First and foremost, the plugs. When were they all gapped last? Should be 0.016"- 0.018" and resistance under 5000 ohms.

Magneto, is the magneto timing different? Anything that retards the spark event, either one mag not firing or plugs way out of spec will create this.

And at 3000' you should not be full rich for takeoff, rather a known to be good target EGT of 1250-1300 assuming all your probes are placed 2-4" from the head.

Now these data points are for nominal 8.5:1 CR engines. If you have a lower compression ratio, then the target value will be higher, about 100dF. And a higher compression engine will be a bit lower.

So double check all these things and report back, along with your CHT's and how they have been behaing over the same time.

Simply, if the CHTs have also been going up, it is a intake leak affecting all cylinders. If they are cooler, it is ignition related (plugs or a mag).

Hope that helps. And attending this would too http://www.advancedpilot.com
 
David is right except for one thing. First....make sure your throttle and mixture are still hitting the stops at the carb.
 
Good call.....yes that is something I suffered first hand, the mixture cable length was so short/ tight the engine pulling on the rubbers flexed the cable mount, and pulled the mixture arm.

You would not find this on the ground because it went full length, but there was no give in the cable. If the full rich mixture position is only just making it and the cable length has no slop in it, you need a different cable or an adjustment.
 
Thanks folks!
David nailed it. I checked timing 1st, but it was dead nuts on. Since i had the #1 plug out anyways, I checked the gap; .022 made it through with no problems. In fact, every plug was over .022. I gapped them to around .018 and went for a flight this afternoon. EGTs are right back to where they should be! I've put over 80hrs on my 6 since buying it 9 months ago. Would the electrodes wear that much in 80hrs?
On a good note, all the plugs were very clean.

Thanks again for the wisdom!
Brian
 
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