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503 low CHT’s dilemma!

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ropermike

Joined: 28 Aug 2006
Posts: 40
Location: West Texas, South Mississippi

Posted: Fri Apr 24, 2009 4:11 am Post subject: 503 low CHT’s dilemma!

I have a puzzler for all you 503 2-stroke guys with a lot more experience with these engines than I. I have a Kolb MkII with a 503 DCDI with 317 hrs. I bought the plane a couple of years ago with 180 hrs on it and entered the 2-stroke world. The engine has always ran excellent for me. I attended a repairmen-inspection coarse a couple of months ago where I complained to the instructor (Brian Carpenter) that my CHT’s where very low and rarely reached 200 F. He said my EIS was probably not working right so this past week I have I set out to get to the bottom of it.



ENGINE DATA

Fuel….fresh reg unleaded.

Oil…... premix with Penn Outdoor Engine Oil 50.1

Plugs…Old plugs not fouled but a little darker than I would like. Installed new plugs.

Carb…Everything is stock. Main jet 155 as per Rotax chart for 3,000 msl at 70*… 2.74      Needle Jets with 8L2 Jet Needles. Needle clip in the top slot. Rubber O-ring on top of clips is installed.

Gauges…EIS digital system with duel CHT’s and EGT’s.

Compression....127 and 123

Prop....66" two blade warp drive.



Before tinkering with the engine, on 70 degree day at 3,000’ msl,  climbout CHT’s were running about 180. EGT’s about 1100. Cruise at 5000 rpm was 170 and 1000.



First, I ran a static test. At full throttle, RPM’s came up to 6800 and started to go over until I backed off. Great! I found the problem! Under propped.



I added a little pitch to my 66” warp drive ground adjustable prop and static tested again. This time RPM was 6200 at full throttle. I thought this would surely bring those CHT’s up. It did, all the way to 200. My EGT’s were running 1050. By the way, OAT was 80 and I ran full throttle for at least 8 minutes until the CHT’s leveled off and would not climb any more. I thought surely my EIS CHT’s was giving me the wrong reading as Brian Carpenter had suggested. 



Next morning, I borrowed a fancy infrared digital temperature gauge, the kind that you point and pull the trigger and put the red dot just where you want to know the temp. I tied up the plane and before I started up, I turned on the master switch and looked at my EIS. CHT’s were both 73*. EGT’s were both 73*. OAT at this time was about 78*. I shot the cyl head as close to the spark plug as I could get with the fancy borrowed handheld infrared temp gauge and it red 73*. Hmmm. I started up and warmed the engine up gradually. When the CHT’s finally reached and leveled off at 200, I idled back and let it cool down a little to 180* then killed the engine. I jumped out and checked the cylinder head with the fancy gauge and it read 188*. I checked and rechecked running back and forth from cyl head to EIS for at least an hr and came to the conclusion my EIS was reading the same as the handheld probe, or at least within 10 degrees….I also ran the engine at 5,000 RPM to check the mid-range. CHT’s would back off to 180 and EGT’s would run about 950* (clip is in the uppermost position on the needle)…..I decided the EIS gauges were good.



I decided then to try a smaller main jet. I took out the 155’s and put in 150’s. (I did not have 152’s). I tested again and topped out at 230* CHT and 1150* EGT at full throttle. RPM’s were 6300 instead of 6200. At 5000 rpm, CHT’s cooled down to 200* and EGT’s were at 1000*. 



I feel the need to have my CHT’s in the 300-375 range. I’m also reluctant to try smaller jets as I’ve been preached at to stay as close to stock and the Rotax charts as possible. I have ordered new needles and needle jets but the old ones look fine. Does anyone have a suggestion as to how to get the CHT’s up or should I just fly the damn thing and quit worrying about it!



Thanks in advance, Mike

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Fri Apr 24, 2009 5:36 am Post subject: Re: 503 low CHT’s dilemma!

 	  ropermike wrote: 	
		  I have a puzzler for all you 503 2-stroke guys with a lot more experience with these engines than I. I have a Kolb MkII with a 503 DCDI with 317 hrs. I bought the plane a couple of years ago with 180 hrs on it and entered the 2-stroke world. The engine has always ran excellent for me. I attended a repairmen-inspection coarse a couple of months ago where I complained to the instructor (Brian Carpenter) that my CHT’s where very low and rarely reached 200 F. He said my EIS was probably not working right so this past week I have I set out to get to the bottom of it.



ENGINE DATA

Fuel….fresh reg unleaded.

Oil…... premix with Penn Outdoor Engine Oil 50.1

Plugs…Old plugs not fouled but a little darker than I would like. Installed new plugs.

Carb…Everything is stock. Main jet 155 as per Rotax chart for 3,000 msl at 70*… 2.74      Needle Jets with 8L2 Jet Needles. Needle clip in the top slot. Rubber O-ring on top of clips is installed.

Gauges…EIS digital system with duel CHT’s and EGT’s.

Compression....127 and 123

Prop....66" two blade warp drive.



Before tinkering with the engine, on 70 degree day at 3,000’ msl,  climbout CHT’s were running about 180. EGT’s about 1100. Cruise at 5000 rpm was 170 and 1000.



First, I ran a static test. At full throttle, RPM’s came up to 6800 and started to go over until I backed off. Great! I found the problem! Under propped.



I added a little pitch to my 66” warp drive ground adjustable prop and static tested again. This time RPM was 6200 at full throttle. I thought this would surely bring those CHT’s up. It did, all the way to 200. My EGT’s were running 1050. By the way, OAT was 80 and I ran full throttle for at least 8 minutes until the CHT’s leveled off and would not climb any more. I thought surely my EIS CHT’s was giving me the wrong reading as Brian Carpenter had suggested. 



Next morning, I borrowed a fancy infrared digital temperature gauge, the kind that you point and pull the trigger and put the red dot just where you want to know the temp. I tied up the plane and before I started up, I turned on the master switch and looked at my EIS. CHT’s were both 73*. EGT’s were both 73*. OAT at this time was about 78*. I shot the cyl head as close to the spark plug as I could get with the fancy borrowed handheld infrared temp gauge and it red 73*. Hmmm. I started up and warmed the engine up gradually. When the CHT’s finally reached and leveled off at 200, I idled back and let it cool down a little to 180* then killed the engine. I jumped out and checked the cylinder head with the fancy gauge and it read 188*. I checked and rechecked running back and forth from cyl head to EIS for at least an hr and came to the conclusion my EIS was reading the same as the handheld probe, or at least within 10 degrees….I also ran the engine at 5,000 RPM to check the mid-range. CHT’s would back off to 180 and EGT’s would run about 950* (clip is in the uppermost position on the needle)…..I decided the EIS gauges were good.



I decided then to try a smaller main jet. I took out the 155’s and put in 150’s. (I did not have 152’s). I tested again and topped out at 230* CHT and 1150* EGT at full throttle. RPM’s were 6300 instead of 6200. At 5000 rpm, CHT’s cooled down to 200* and EGT’s were at 1000*. 



I feel the need to have my CHT’s in the 300-375 range. I’m also reluctant to try smaller jets as I’ve been preached at to stay as close to stock and the Rotax charts as possible. I have ordered new needles and needle jets but the old ones look fine. Does anyone have a suggestion as to how to get the CHT’s up or should I just fly the damn thing and quit worrying about it!



Thanks in advance, Mike 	




Are those temps centigrade? If so, 200 would be 392F, not anomolous but pretty close to siezure.....



You want the CHT's to be around 300F and this is generally where the 503 will run after it's broken in with correct jetting and propping. Your EGT's and propping sound about right, 1050 to 1150 is pretty good (I liked it 1050 to 1100). 

325F is the limit of my personal comfort (but still ok) and 350F is where I land and start looking for a problem. 375 to 400F will bring that TBO way way down below the rated 300 hours......



So that's my WAG - you're measuring in C?



LS

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LS
Titan II SS

ropermike

Joined: 28 Aug 2006
Posts: 40
Location: West Texas, South Mississippi

Posted: Fri Apr 24, 2009 6:48 am Post subject: Re: 503 low CHT’s dilemma!

I do not have an operators manual for the EIS system but I have gone thru all the menus and cant find any way for it to be changed to Centigrade.....I believe it to be measuring in F because the hand held infrared temp gauge confirmed the readings in F, it actually says F on the digital readout....I agree with your CHT preferences.....Thanks

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The next best thing to playing and winning is playing and losing!...Mike Hillger

olendorf

Joined: 06 Jul 2006
Posts: 140
Location: Schenectady, NY USA

Posted: Fri Apr 24, 2009 12:54 pm Post subject: Re: 503 low CHT’s dilemma!

Try putting your CHT sender in a can of boiling water and see what reading you get.

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Scott Olendorf
Original Firestar, Rotax 447, Powerfin prop
Schenectady, NY
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