high cht egt

The Lycoming o320 on my RV7a runs great at full throttle and mixture at peak. When I reduce the RPM in cruise, the CHT and EGT began to climb. CHT reaches 402-406 and EGT 1250 - 1400. Other cylinders stay pretty constant. Oil temp and pressure are normal. I have a cowl flap and that helps the cooling. I can't figure why temps would climb when I reduce the throttle and lower my rpms. 1200 hours on the engine. Any thoughts?

Carbed engines are notoriously bad at fuel distribution. My #1&2 CHTs are high when firewall throttled. My #3&4 are hot when throttle pulled back a bit. What might be happening for you is that your hot cylinders are running leaner in a particular throttle position. Not sure that there's much you can do about it, although some say a bit of carb heat can help re-distribute the fuel a bit more evenly. I've had some mixed success with that myself.

Before you go too much further, I would give you the customary advice to make sure your baffling is as good as it can possibly be and that you've made sure you've got air flowing around the frontside of #2 and the backside of #3 where the fin depth is sometimes non-existent.

Hope this helps.

Electronic ignition? If so, you may want to reduce the advance at cruise RPM/MAP.

pmags

yes, I have two pmags.

Lots of info in other threads on this. Make sure you have the jumper installed for the A curve but even better is to make a serial connection via your laptop and the free EICAD program (free download) to program the Adv Shift and Max Advance.

Instructions for the cable are available on the EMAG website.

rwarre said:

yes, I have two pmags.

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Do you have the jumper installed and are they timed to TDC?

Have you retimed the P-mags recently?

If this continues, contact me off list and I can help you turn them down one notch. Those that have done this have found their CHT's have come into line and they have picked up a little speed.

rwarre said:

The Lycoming o320 on my RV7a runs great at full throttle and mixture at peak. When I reduce the RPM in cruise, the CHT and EGT began to climb. CHT reaches 402-406 and EGT 1250 - 1400. Other cylinders stay pretty constant. Oil temp and pressure are normal. I have a cowl flap and that helps the cooling. I can't figure why temps would climb when I reduce the throttle and lower my rpms. 1200 hours on the engine. Any thoughts?

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This post suggests the problem is on one cylinder not all of them.

I would strongly suggest that you are seeing a cylinder that would have been ROP and when you reduce throttle, and create less MP inside the intake than is outside, air is leaking in through a intake gasket or the rubber coupling.

If you have the black coloured Lycoming gaskets, replace ALL of them with the red coloured SUPERIOR gaskets. They are far superior.

Let us know what you find.

Economizer System

At full throttle, the carburetor is at a richer setting due to the economizer system design. As throttle is reduced, the mixture becomes more lean. You may need to readjust your mixture at the lower throttle setting.

Ellis