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Intermittent stumble on O-235-C1

One little troubleshooting tool I have used is trying a bit of carb heat, sometimes satisfies a fussy carburetor. I would expect the carb overhaul should have made if at least different but ?
On my own Pa-12, I had a similar problem and got mad enough to just tear it down and go thru it, valve train was not as good as should have been. As an A&P/IA it wasn't such a big deal but just hard headed enough I wouldn't put up with the kicks in flight.
Decided I needed to fly more or not at all, the other hobbies pretty much won for now,
Ken
 
Hey LanaT

Please let us know what the problem turned out to be. The info on the troubleshooting process and the ultimate fix is extremely helpful to others here that may run across similar problems.

Web
 
wireweinie said:
Hey LanaT

Please let us know what the problem turned out to be. The info on the troubleshooting process and the ultimate fix is extremely helpful to others here that may run across similar problems.

Web
Click to expand...

I'll let you know if I ever figure it out myself. Still a mystery.
 
Primer check valve stuck and leaking through.. Cap the lines and go out and fly it again!
 
Last edited:
Try soaking some Aerokroil or Mouse Milk on the valves. See if it makes any difference. Not a permanent fix however if a reamer is needed.

Gary
 
I'm not sure if you have looked at your valve springs or not, but a long time ago in my cub with an 0235C-1, I had an intermittent miss. I was a kid from AK in a J-3 on the East Coast.
The guys at Sussex, NJ told me that sometimes the inner springs break on those engines and you can't see it. They said that dual springs are to cover for all harmonics and if a spring is broken then sometimes you hit the right harmonics and get a miss. I took their advice, traded labor for expertise and tools, and sure enough, found a couple of broken inner valve springs.
I don't know if that was the cause or not, but it didn't happen again. As an aside... they also told me to expect a small crack from the spark plug hole toward the (I think I remember) exhaust port. Yep they were right about that too. They said almost all have it. Mine did. On their advice, I put it back together and flew back to CA to rebuild it the next winter. It didn't stumble after I put serviceable springs in it. Chances are, this is not your cause, but since the thread brought back the memory of your description, I thought I'd throw it out there..
Jose
 
Ken Robbins said:
One little troubleshooting tool I have used is trying a bit of carb heat, sometimes satisfies a fussy carburetor. I would expect the carb overhaul should have made if at least different but ?
On my own Pa-12, I had a similar problem and got mad enough to just tear it down and go thru it, valve train was not as good as should have been. As an A&P/IA it wasn't such a big deal but just hard headed enough I wouldn't put up with the kicks in flight.
Decided I needed to fly more or not at all, the other hobbies pretty much won for now,
Ken
Click to expand...

Did this tear down and rebuild fix the problem?


Sent from my iPhone using SuperCub.Org mobile app
 
UPDATE: I realized that I never posted what the conclusion was!

So in my post I claimed that my engine was an O-235-C1. This was mostly true-- when it had a propstrike a number of years ago, the shop complied with the Service Instruction to convert the O-235-C to an O-235-C1. In the service bulletin it requires, I believe, a different cam, maybe different piston rings... Not 100% sure (if anyone would like to know the details, I know have the service instruction lying around somewhere). HOWEVER, in this service instruction it says you MUST change the carburetor to comply fully with the conversion. In the notes in my logbook it became clear that neither the previous owner, nor the shop who did the work, actually changed the carburetor. It had the same model number, MA3A, but the 10-XXXX part number was different. And, thus, the float bowl assembly was different, and thus the mixture needle seated differently, and THUS when I put the correct carburetor on my (now entirely compliant) O-235-C1, I haven't had a single miss/stumble since. I spent my ENTIRE summer on this. Shoddy maintenance/past owners can be SO frustrating. Now I'm down for my first annual and I figured I should update this, in case anyone has similar issues in the future
 
lanat said:
UPDATE: I realized that I never posted what the conclusion was!

So in my post I claimed that my engine was an O-235-C1. This was mostly true-- when it had a propstrike a number of years ago, the shop complied with the Service Instruction to convert the O-235-C to an O-235-C1. In the service bulletin it requires, I believe, a different cam, maybe different piston rings... Not 100% sure (if anyone would like to know the details, I know have the service instruction lying around somewhere). HOWEVER, in this service instruction it says you MUST change the carburetor to comply fully with the conversion. In the notes in my logbook it became clear that neither the previous owner, nor the shop who did the work, actually changed the carburetor. It had the same model number, MA3A, but the 10-XXXX part number was different. And, thus, the float bowl assembly was different, and thus the mixture needle seated differently, and THUS when I put the correct carburetor on my (now entirely compliant) O-235-C1, I haven't had a single miss/stumble since. I spent my ENTIRE summer on this. Shoddy maintenance/past owners can be SO frustrating. Now I'm down for my first annual and I figured I should update this, in case anyone has similar issues in the future
Click to expand...

GREAT news this is now sorted out and thank you for sharing the solution with us!!! Could you please post the service bulletin number? I have an O-235-C sitting in my workshop and maybe interested in modifying it :)
 
Lanat, Thanks for starting this thread. I have identical problems with my O-235 C2C on my PA-12. The hickup doesn't start until it's warm and RPM about 2200 ish. it is sooo annoying because that is the perfect RPM to fly formation with all of my buddies.
- Thought it was the primer lines at first because i've had a few break but they are all fixed up and still the same issue.
-Carb heat slows the frequency.
-Haven't tried to go to a single mag.
-50 Hours only on a rebuilt motor.
-Carburetor is a direct match per the Marvel Schebler website.
-Carburetor has been gone through with new float conversion.
-Mags rebuilt and timed perfectly.
-The sound is like it's running lean for a moment...

Might try Marvels Mystery oil to see if that helps.
Any other thoughts? Nic
 
How do the plugs look? Are they indicating it's running lean?

The other couple of tips that I got, that I never had to look into, were cracked cylinder heads on the intake side, causing a slight intake leak when the cylinder head temp is high enough to flex and allow air through the crack. Have you checked for other intake leaks? Is the line that goes from the strainer to the carb getting hot/is the line old and degraded? Sometimes the fuel line expands over time and the carb is starved of fuel. Check for venting issues too, is there vapor lock? Are your caps properly vented?

This was SUCH a frustrating job for me, so I wish you luck and keep us all updated.
 
Do a mag check at 2200 and 2400 might have a bad plug that fires well at sunup but cuts out at higher RPM. If you have slick mags recheck the internal timing. DENNY
 
Wow, 2 responses in minutes. All great suggestions...frustrating indeed
-Plugs looked normal this annual. New with the engine install. Cleaned, tested, rotated, replaced.
-I'll check the intakes.
-Fuel line from strainer is new.
-2 new fuel caps.
-Ill try the mag check at higher RPM
-They are slick mags.


The problem started like clockwork on the first flight of the new motor. It seems to be worse in the summer when it's running hotter. It doesn't stumble until 20 min or so into the flight. It stumbles in climb under a load as well as the decent. Otherwise it runs great with lots of power. All compressions are great. 78/80 I've never felt that the engine would quit but it is annoying. We thought it would get better as we put hours on it and properly broke in the motor but no luck. Rich mixture and winter time seems to help so I think the intake is the next best place to focus on. Thanks!
 
+++ on the inflight mag check. Also try applying carb heat when it stumbles - if the then richer mixture helps it might indicate if it's going lean. If it gets worse with carb heat it may be going too rich. Experiment.

Gary
 
How old are the mags?
Or how old are the capacitors in them?
Capacitors do fail as they age, first indication when mags are fully warm or if you are flying at higher flight levels than usually (normally not a problem on a Cub).

Do not ask my why I know

Orri
 
Orri said:
How old are the mags?
Or how old are the capacitors in them?
Capacitors do fail as they age, first indication when mags are fully warm or if you are flying at higher flight levels than usually (normally not a problem on a Cub).

Do not ask my why I know

Orri
Click to expand...

I sent the mags off for rebuild as we installed the engine. They didn’t have a lot of time on them but the airplane sat in a barn for 15 years when I bought it so it was a necessary expense. I assume all of that was replaced...I’ll double check the paperwork
 
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