High EGTs??

Hi Guys.

I have a new Aerosport Power 0-320, carb, and a 3 blade Catto Prop.
TT on engine is 120 hours.

In the past 20 hours I have noticed that during climb and very high power settings that the EGTs on cyls 3 and 4 go quickly past 1500, and have been as high as 1575.

I have searched other posts, and an induction leak causing mixture leaning seems to be the mail suspect issue here.

My questions are:
1. how do you check for an induction leak?
2. what are the main areas to check?

Thanks,
Tom Sampson
Portland, Oregon

Tom,

Induction leaks on your engine will be either at the carburetor gasket, intake flange gasket or intake pipe hose where it's mounted to the sump. Generally it will be pretty obvious just looking at it. Kind of rare for an induction leak to be causing your 2 rear cylinders to have high EGT's. Call Bart

Allen

High EGT can be caused by spark plugs being fouled, of other ignition problems in the wiring not getting a good spark. This is listed in my EDM-700 manual and Sacramento Sky Ranch book. I had a cylinder that had high EGT right in the middle of a flight and it was the fuel injection nozzle being partially blocked.

Tom Sampson said:

In the past 20 hours I have noticed that during climb and very high power settings that the EGTs on cyls 3 and 4 go quickly past 1500, and have been as high as 1575.

Click to expand...

Is it possible that the probes are to be at fault? I have one probe from GRT that doesn't work at low temps. It did a very good job or faking a problem but sense I had gone down that road before I checked the probe first. Sure enough it acted the same way in each exhaust I used it with.

Do you have duel electric ignition? Is it possible that one ignition is hooked up to only two cylinders.

High EGT? May be not, (probe location)

High EGT? Is it really high? May be not


Obviously "relative"" is key between cylinder, if you have the probes in the same location in each pipe.

What are EGT's on cylinders #1 and #2? (If spread is ator less than 170F it may be OK, not great but OK.)

Where do you have the probes? (2" or 5" down from flange for example)?

What are the CHT's? (are the CHT's high as wtih a large spread.)

Mo info needed but it might be nothing to some of the above or comment below.

Possible problem:

I would check the mixture first.

O-320's are known to run lean in RV's with the free flow airbox and exhaust. The stock MS carbs just don't have enough jet to feed the extra air flow at higher power. There is no screw to adjust, it's the main jet. I can help you with that if you like. Look up the serial # on the carb and write me. Not all MA-4SPA's are the same. The fix is pretty simple. It does require partial dis-assembly (drop the bowl and remove main jet) and a "mod" drilling-out of the main jet slightly. A very common problem and even more common fix. Typical carbs for a Cessna or Piper are not rich enough for RV's. All this is well documented. Precision Airmotive (the owner of the Marvel Schibler carb line) will officially say no, but on the side they know all about it, they just can't "approve it". In the spirit of full disclosure you can trade in your carb for a richer on (if that is the problem), but that fix might cost $1,600. You can get the richest carb they sell and still have issues. Drilling the main jet works and cost about $5-$10 for new clips, washers and gaskets.

Have you done a LEAN test?



Bottom line 1500-1600F max EGT has been reported by other RV'ers. However to be clear you should not see peak EGT at take-off power. If you have checked the mixture, your probes are close to exhaust port and the spread is small, you may be OK. You should look at the plugs, induction leaks and timing, but don't go crazy. You have to get all the data first.

PS is the throttle FULL open? Check that.

High egt on individual cylinders during climb power climb power could be:
Lean
Running on one mag or ignition system instead of two due to bad system or fouled plug or plug that won't fire at high power,
timing,
bad valve seating to the valve seats from worn guides or other reason.
Exhaust leak near the probe allowing exhaust gases to be re-ignited in the pipe.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."