twoeightfive
MEMBER
Eagle River, AK
Hey everyone I have a pretty weird issue happening with my cub. I have a 1976 PA-18 160 HP cub with a pretty new engine only about 250smoh which was done in January of 21’. Have not had any huge issues with it at all the engine itself has been great so far knock on wood.
I apologize for the long post in advance but I figured the details matter with this. If you care to read the whole thing I’m sure you may be intrigued as well.
For those of you from Alaska you probably know we’ve had a pretty rainy summer as of late. I usually fly the heck out of my cub when I’m not flying at my other pilot job. Anyways this July I didn’t fly it for about 2.5 weeks because of crappy weather with non stop rain and work getting in the way. When I finally got around to flying it again at the end of July I started it up and it had a huge backfire that got my attention. I didn’t do anything different than I usually do with the start. Primed it 2 times with my primer and cranked it over. It ran smooth afterwards so I didn’t think too much of it.
When I taxi’d over to do my run up everything was fine with the mag check, I have new bendix mags. Then I went to do the carb heat check at 1700-1800rpm ish and instantly as I pulled the carb heat the engine sputtered and quit. I was pretty surprised at first I tried to chock it up to maybe being too rich since it was a hot sunny day but I’ve flown my cub on lots of hot sunny days and never had any issues with it. I then restarted it and did the run up again and checked carb heat and it then dropped 400-500rpm and was just spitting and sputtering. Then it gradually smoothed out and ran okay. I shut it down and hopped out and popped the cowling.
I wiggled my carb filter to make sure it wasn’t loose, it was tight. I checked for blue stains on the carb itself, it was clean. Called my mechanic and I thought that maybe it was water in the carb somehow and he agreed that it was likely but without looking at it couldn’t say for sure. I started it back up and ran it up 2 more times and the carb heat would work normally and the engine would not quit. It ran normal like this never even happened. So I opted to fly it around the pattern and checked everything in the air and sure enough it worked as normal. No issues at all.
I flew it the next day again in the pattern and the first run up the carb heat dropped the RPM 400ish and it ran rough but didn’t kill the engine. Subsequent carb heat drops were normal after that and everything worked fine. Flew it and it worked great like it never even happened.
I had two hypotheses, one that water got into the carb heat box somehow, or two that I maybe had a primer leak that was causing it to run too rich to where carb heat would kill it but I wasn’t sure why it wouldn’t replicate in flight.
Mechanic and I pulled the carb air filter and it was fine. We also then pulled the scat tube coming from
the exhaust shroud that goes to the carb heat box and saw standing water drops in the hose. And we were pretty convinced that water was dripping down the baffling into the exhaust shroud and into that hose. Even though it’s angled up it does have a low spot or 2 in it to where water could sit. We blew out the water with compressed air. The carb heat box has drain holes of course but maybe enough water is coming through it just doesn’t matter.
My question is this: has anyone else had issues with their Sutton exhaust like this ? I have had this exhaust for 3 years now and probably flown it 550 hours with no issues until now. To be fair the plane used to live in a hangar but now stays outside. It’s also been a pretty rainy summer definitely more so than usual.
I know the Sutton exhaust heat shroud for the carb heat and cabin heat air is open ended on the back end of the left side at least (not sure about the right) and we did a little experiment and poured a small amount of water on the top of the left side of the baffling (#2 and #4 cylinder side) and watched it drop a bit down into the open end of the exhaust and make its way to where that scat tube connects. As with other Sutton exhaust applications there is the relocation of the air scoop for carb heat and cabin heat into the top of the #1 cylinder side baffling. So maybe water is leaking in from
there too. I know others that have the Sutton who have had no issues flying in this rain lately so I’m not sure what’s so special about mine. When comparing to a friends Sutton with a brand new engine his scat hose is perfectly aligned and has no low spots whatsoever except for the very inlet at the shroud. Maybe replacing the hose is the right answer ? Sorry for rambling just lots of thoughts here as to what the issue could be. It is still happening after rainy days and just happens for the first 1-2 applications of carb heat then runs normal.
Attached below are photos of a buddies Sutton exhaust, mine is the exact same except maybe my Scat tube is a little more weathered. You can see how the inlet for the carb heat is open and exposed with the shroud to where water could get in. But I would think it would also be able to get in at the relocated air scoop as well in the baffling. It’s been a week since we cleaned the tube out and today it quit on me again during run up after some good rain. As much as I’d like to say a solution would be to just buy a hangar or don’t fly it after it rains I think it’s obnoxious it happens in the first place and I don’t have warm fuzzies about ingesting water all the time on start.
I apologize for the long post in advance but I figured the details matter with this. If you care to read the whole thing I’m sure you may be intrigued as well.
For those of you from Alaska you probably know we’ve had a pretty rainy summer as of late. I usually fly the heck out of my cub when I’m not flying at my other pilot job. Anyways this July I didn’t fly it for about 2.5 weeks because of crappy weather with non stop rain and work getting in the way. When I finally got around to flying it again at the end of July I started it up and it had a huge backfire that got my attention. I didn’t do anything different than I usually do with the start. Primed it 2 times with my primer and cranked it over. It ran smooth afterwards so I didn’t think too much of it.
When I taxi’d over to do my run up everything was fine with the mag check, I have new bendix mags. Then I went to do the carb heat check at 1700-1800rpm ish and instantly as I pulled the carb heat the engine sputtered and quit. I was pretty surprised at first I tried to chock it up to maybe being too rich since it was a hot sunny day but I’ve flown my cub on lots of hot sunny days and never had any issues with it. I then restarted it and did the run up again and checked carb heat and it then dropped 400-500rpm and was just spitting and sputtering. Then it gradually smoothed out and ran okay. I shut it down and hopped out and popped the cowling.
I wiggled my carb filter to make sure it wasn’t loose, it was tight. I checked for blue stains on the carb itself, it was clean. Called my mechanic and I thought that maybe it was water in the carb somehow and he agreed that it was likely but without looking at it couldn’t say for sure. I started it back up and ran it up 2 more times and the carb heat would work normally and the engine would not quit. It ran normal like this never even happened. So I opted to fly it around the pattern and checked everything in the air and sure enough it worked as normal. No issues at all.
I flew it the next day again in the pattern and the first run up the carb heat dropped the RPM 400ish and it ran rough but didn’t kill the engine. Subsequent carb heat drops were normal after that and everything worked fine. Flew it and it worked great like it never even happened.
I had two hypotheses, one that water got into the carb heat box somehow, or two that I maybe had a primer leak that was causing it to run too rich to where carb heat would kill it but I wasn’t sure why it wouldn’t replicate in flight.
Mechanic and I pulled the carb air filter and it was fine. We also then pulled the scat tube coming from
the exhaust shroud that goes to the carb heat box and saw standing water drops in the hose. And we were pretty convinced that water was dripping down the baffling into the exhaust shroud and into that hose. Even though it’s angled up it does have a low spot or 2 in it to where water could sit. We blew out the water with compressed air. The carb heat box has drain holes of course but maybe enough water is coming through it just doesn’t matter.
My question is this: has anyone else had issues with their Sutton exhaust like this ? I have had this exhaust for 3 years now and probably flown it 550 hours with no issues until now. To be fair the plane used to live in a hangar but now stays outside. It’s also been a pretty rainy summer definitely more so than usual.
I know the Sutton exhaust heat shroud for the carb heat and cabin heat air is open ended on the back end of the left side at least (not sure about the right) and we did a little experiment and poured a small amount of water on the top of the left side of the baffling (#2 and #4 cylinder side) and watched it drop a bit down into the open end of the exhaust and make its way to where that scat tube connects. As with other Sutton exhaust applications there is the relocation of the air scoop for carb heat and cabin heat into the top of the #1 cylinder side baffling. So maybe water is leaking in from
there too. I know others that have the Sutton who have had no issues flying in this rain lately so I’m not sure what’s so special about mine. When comparing to a friends Sutton with a brand new engine his scat hose is perfectly aligned and has no low spots whatsoever except for the very inlet at the shroud. Maybe replacing the hose is the right answer ? Sorry for rambling just lots of thoughts here as to what the issue could be. It is still happening after rainy days and just happens for the first 1-2 applications of carb heat then runs normal.
Attached below are photos of a buddies Sutton exhaust, mine is the exact same except maybe my Scat tube is a little more weathered. You can see how the inlet for the carb heat is open and exposed with the shroud to where water could get in. But I would think it would also be able to get in at the relocated air scoop as well in the baffling. It’s been a week since we cleaned the tube out and today it quit on me again during run up after some good rain. As much as I’d like to say a solution would be to just buy a hangar or don’t fly it after it rains I think it’s obnoxious it happens in the first place and I don’t have warm fuzzies about ingesting water all the time on start.
Attachments
Last edited:
