Crazy EGTs

[petep]

Been trying to tune my Aeroinjector for several weeks with little success. Started with a #2 need could get anywhere near WOT before the back two cylinders blew thru 1400 EGT. Went to a 2.5 and saw some improvement but still the same issue with rear cylinders high EGTs. Now on a #3 needle any can get the back two cylinders to WOT at 1385 or so while the front two are barely 1200 at full rich mixture. Suspect a bogus EGT indication but not willing to fry the engine based on that assumption. I have double checked the usual suspects, ie induction leaks, valve lashing, ignition timing, leak down check ,mixture arm position and travel and EGT probe position.

Sent all this data to Sonex yesterday but don't expect to hear from them until after the holidays. Anyone think of anything else I might check in the interim?

[mike.smith]

Been trying to tune my Aeroinjector for several weeks with little success. Started with a #2 need could get anywhere near WOT before the back two cylinders blew thru 1400 EGT. Went to a 2.5 and saw some improvement but still the same issue with rear cylinders high EGTs. Now on a #3 needle any can get the back two cylinders to WOT at 1385 or so while the front two are barely 1200. Suspect a bogus EGT indication but not willing to fry the engine based on that assumption. I have double checked the usual suspects, ie induction leaks, valve lashing, ignition timing, leak down check and mixture arm position and travel.

Sent all this data to Sonex yesterday but don't expect to hear from them until after the holidays. Anyone think of anything else I might check in the interim?

What were your CHTs like? That's what really matters.

[petep]

CHTs seem to be OK but with he rear two EGT going past 1400 on the way to 1450 plus I have not had the nerve to stay at WOT long enought to get a stabilized CHT.

[mike.smith]

CHTs are what matters. I'm sure you've seen the Mike Busch link often posted on the forum, discussing EGTs. You can get your CHTs to drop very quickly by backing off the throttle and pushing the nose down, so you might give WOT a longer try and watch the CHTs.

[Onex107]

I have my #3 needle adjusted a little richer so that my mixture is set about half way for normal wot. Then, on climb out I can go a little richer to cool off the egt's and go a little leaner at cruise to put the egt's in the 1250 - 1325 range and the cht's in the 280-325 range.
I then get a 1000 rpm idle, after landing, with no mixture change. Plus, no seasonal change.
200 hours and counting.
Onex 107

[lutorm]

Now on a #3 needle any can get the back two cylinders to WOT at 1385 or so while the front two are barely 1200 at full rich mixture.

Sounds like the same outrageously uneven mixture distribution we saw on our Aerovee with the stock intake (see the "Temperature Balancing by Turning/Twisting the Carb" thread in this forum.) The real test would be to lean it from that condition. When I did that on our engine, the back EGTs dropped while the front ones climbed -- clear indication that the back cylinders were already running lean of peak at full rich. I don't think that's a condition that's at all conducive to engine longevity.

[petep]

Resolved. Believe it or not the AeroInjector would not tune if I ran it up with the cowl off. Put the cowl on and all four EGTs lined up with 20 or so degrees. Of course now I have top go back and undo all the enriching I did trying to get the back two EGT down. Bottom line is that with the cowl off and running at WOT the back two cylinders would consistently run 200 to 250 degrees hotter that the from two cylinders. This puppy does not like turbulent air at the intake.
Thanks for all the suggestions,
Pete

[Gordon]

Cowl Off Runup.............FYI

A suggestion Pete........it is risky running any of these engines with the cowl OFF due to poor cylinder cooling. On the Lycomings we NEVER test run them with the cowl off due to "hot spots" and possible long term heat damage that may not show up until later.

Always have the bottom cowl on AND the top cowl on to get the proper air flow DOWN through the cylinders.

Gordon........Onex........Hummel 2400

[petep]

Always use a large cow catcher to isnure proper cooling. Same way Lycoming taught us 50 years ago.

[rizzz]

Check your air filter as well, I had high EGTs on one side after replacing the air filter on my aerocarb. It must have been a torn or something causing the air to swirl unevenly in the manifold and favouring one side over the other.