Carb heat cable & mid-range engine stumble
The fuel isnt super old... I was less than half full when I started yesterday, and filled up twice, all with the same result. I havent totally drained the tanks, but Ive ran a few tank-fulls through since this all started.
Im running the Lycoming 0-235C.
It ran like a top till one day in September, when all of a sudden this happened. Like I said, Im at a loss... Frustrating is an understatement !
Bob K.
Anchorage, AK
Im running the Lycoming 0-235C.
It ran like a top till one day in September, when all of a sudden this happened. Like I said, Im at a loss... Frustrating is an understatement !
Bob K.
Anchorage, AK
Bob,
When you have time, please do a run up. Pls listen for any differences in each magneto while running on single mag.
While this does sound like a mixture or carb issue, I have seen situations where a weak ignition system runs fine at lower power levels but once you get to a certain point falls flat and will not go any higher.
Joe A
When you have time, please do a run up. Pls listen for any differences in each magneto while running on single mag.
While this does sound like a mixture or carb issue, I have seen situations where a weak ignition system runs fine at lower power levels but once you get to a certain point falls flat and will not go any higher.
Joe A
Could be...
This sounds like it could be the result of weak or broken valve springs. Check them out.
Mike
Mike
Fuel delivery/
Is it possible that the fuel is getting disrupted before it gets to the carb when you pour the coals to it? Are there any blockages in the fuel lines?
High time engine
Bob,
As recall the guy that bought your plane from Norm Stout was an mechanic and only rebuilt the top. Your engine only had 70 hrs on it when my dad sold it to Norm Stout.
As recall the guy that bought your plane from Norm Stout was an mechanic and only rebuilt the top. Your engine only had 70 hrs on it when my dad sold it to Norm Stout.
Joe- I'll do a very scientific run-up next time to see if I can hear any strangeness due to the mags. I know its really a long shot that the mags could be causing this, but...
Mike-A mechanic pulled the valve covers and checked out the springs/valves, at least visually. He didn't test any of the springs specifically, but they all appeared to be fine.
Boot-Ive been meaning to reply to your PM... That's pretty awesome that your dad rebuilt this plane ! I haven't ran the numbers to see how much time the engine actually has on it, but I do remember talking to the previous owner about how the bottom end hasn't been touched in a long time. The guy who bought it from Norm said he pulled a jug, and everything looked really good in the lower-end. The mechanic who checked out the valve springs also pulled the fuel supply line from the carb to check the flow, and all was well.
I talked to a friend who described similar symptoms on his newly rebuilt engine, which turned out to be the idle air screw had backed all the way out. That shouldn't be the case, because the carb was just gone through, but I'll check it out next time as well.
Thanks again for all the suggestions ! Hopefully it will be something easy...
Bob K.
Anchorage, AK
Mike-A mechanic pulled the valve covers and checked out the springs/valves, at least visually. He didn't test any of the springs specifically, but they all appeared to be fine.
Boot-Ive been meaning to reply to your PM... That's pretty awesome that your dad rebuilt this plane ! I haven't ran the numbers to see how much time the engine actually has on it, but I do remember talking to the previous owner about how the bottom end hasn't been touched in a long time. The guy who bought it from Norm said he pulled a jug, and everything looked really good in the lower-end. The mechanic who checked out the valve springs also pulled the fuel supply line from the carb to check the flow, and all was well.
I talked to a friend who described similar symptoms on his newly rebuilt engine, which turned out to be the idle air screw had backed all the way out. That shouldn't be the case, because the carb was just gone through, but I'll check it out next time as well.
Thanks again for all the suggestions ! Hopefully it will be something easy...
Bob K.
Anchorage, AK
Bob,
It is a stretch but something similar happened to me with my Stinson years ago.
All checked out well at runup but I would lose power just about the time I reached full take off power.
Turned out that the spark plug gap was too great. I regapped the plugs and it ran like a trooper.
The only thing unusual is the Franklin engine uses auto type plugs instead of the double pronged aero type.
It is a stretch but something similar happened to me with my Stinson years ago.
All checked out well at runup but I would lose power just about the time I reached full take off power.
Turned out that the spark plug gap was too great. I regapped the plugs and it ran like a trooper.
The only thing unusual is the Franklin engine uses auto type plugs instead of the double pronged aero type.
Gus Causbie
Ash Flat, AR
N83564, 7AC-2235, A65-8
Ash Flat, AR
N83564, 7AC-2235, A65-8
Still no luck in finding the culprit...
In the heart of a BEAUTIFUL ski-season, I very reluctantly swapped the skis out for wheels yesterday afternoon, so I can take it back to a shop and have them dig into it.
When I started it up, it absolutely would not go over 1500rpm, even with the carb heat pulled. After it warmed up about 10 minutes later, I goosed it, and it ran up to full RPM. Even after it was warm, it still just wouldn't smoothly transition between idle and full throttle. It was slightly better transitioning with carb heat pulled, but still not as smooth as before all this started.
I spoke with the mechanic I'll be taking it to, and he was saying that since my carb is an MA-3a without an accelerator pump, that ANY throttle changes should be accompanied with carb heat. I never had to use constant carb heat for smooth throttle transitions before this started in September, and dont plan on accepting that as a solution. He then asked if it just started doing this in the cold weather, and I told him that it started back in September (+/-40°). However, it never had any of these symptoms the previous winter season.
A run-up on each mag had no affect on the issue throughout the rpm range. I'm almost 100% convinced that I still have a carburetor issue. This mechanic says he has another MA-3 carb that he can throw on to see if it fixes the problem, and will also check the jetting. I'm hopeful....
A couple things that make me scratch my head are that on my last flight (post carb-rebuild) when I pulled the mixture cable to lean a bit, it didn't want to lean very much before it started running noticeably rougher. Granted, it could be when the mixture cable was re-attached it had less slack in it, etc, but I made sure that the range of motion was complete on the mixture lever. Also, when pulling carb heat, the rpm doesn't seem to drop quite as far as it used to, before all this started. It still drops slightly, but not as noticeably as before. Both of those things could be just my imagination REACHING for symptom ideas, but still...
Thanks for all the ideas and suggestions ! I'll keep updating as I find out more.
Bob K.
Anchorage, AK
In the heart of a BEAUTIFUL ski-season, I very reluctantly swapped the skis out for wheels yesterday afternoon, so I can take it back to a shop and have them dig into it.
When I started it up, it absolutely would not go over 1500rpm, even with the carb heat pulled. After it warmed up about 10 minutes later, I goosed it, and it ran up to full RPM. Even after it was warm, it still just wouldn't smoothly transition between idle and full throttle. It was slightly better transitioning with carb heat pulled, but still not as smooth as before all this started.
I spoke with the mechanic I'll be taking it to, and he was saying that since my carb is an MA-3a without an accelerator pump, that ANY throttle changes should be accompanied with carb heat. I never had to use constant carb heat for smooth throttle transitions before this started in September, and dont plan on accepting that as a solution. He then asked if it just started doing this in the cold weather, and I told him that it started back in September (+/-40°). However, it never had any of these symptoms the previous winter season.
A run-up on each mag had no affect on the issue throughout the rpm range. I'm almost 100% convinced that I still have a carburetor issue. This mechanic says he has another MA-3 carb that he can throw on to see if it fixes the problem, and will also check the jetting. I'm hopeful....
A couple things that make me scratch my head are that on my last flight (post carb-rebuild) when I pulled the mixture cable to lean a bit, it didn't want to lean very much before it started running noticeably rougher. Granted, it could be when the mixture cable was re-attached it had less slack in it, etc, but I made sure that the range of motion was complete on the mixture lever. Also, when pulling carb heat, the rpm doesn't seem to drop quite as far as it used to, before all this started. It still drops slightly, but not as noticeably as before. Both of those things could be just my imagination REACHING for symptom ideas, but still...
Thanks for all the ideas and suggestions ! I'll keep updating as I find out more.
Bob K.
Anchorage, AK
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I'm no expert by any stretch of the imagination. But have read several accounts of similar symptoms which you are having. And if I recall correctly in almost every single case it was a carb problem.
I know Bill Pancake has solved several of these mystery's and the culprit is usually some debris, rust etc in some little know orifice or passage ways inj the carb. And I think a couple of these occurred after a carb "rebuild" just like your situation.
You definately should not accept you have to put on carb heat with ANY power change.
Seems like a lean condition and a cloggged passage way somewhere in the carb would seem reasonable to investigate.
I know Bill Pancake has solved several of these mystery's and the culprit is usually some debris, rust etc in some little know orifice or passage ways inj the carb. And I think a couple of these occurred after a carb "rebuild" just like your situation.
You definately should not accept you have to put on carb heat with ANY power change.
Seems like a lean condition and a cloggged passage way somewhere in the carb would seem reasonable to investigate.
Leaded gas has allways been the root of a lot of engine problems.BobK wrote:I was afraid of that...
Ive always run 100ll, so I cant place the blame on it, and Ive done the MMO deal on rare occasions already.
Ive rebuilt my share of Holleys and Quadrapukes, so it just pains me to think of how much $$$ is involved in rebuilding simple airplane carbs.
Thanks all for your help ! I'll call my mechanic and see what my options are.
Hasta ~
Bob K.
Anchorage, AK
Our "Airknockers" ae supposed to have 80 octane, but as that's not available around here we gotta run 100LL which contains much more lead.
Car gas works nicely, but the Alcohol content makes it dangerous to run, so we're stuck with 100ll. And the lead tends to foul everything, not just spark plugs.
Thanx
Shorty
Shorty
Shorty,
There is a AD or SL (I forget which) to check under the carb heat muff on the Cherokee for exhaust leaks. Apparently, the pipes tend to crack under the muff after a period of time. Obviously, that would cause a rough engine when the carb heat is pulled.
That being said, my Cheokee always seemed richer than necessary with the carb heat pulled too but it was like that for the 25 years I owned it.
Mike Berg
There is a AD or SL (I forget which) to check under the carb heat muff on the Cherokee for exhaust leaks. Apparently, the pipes tend to crack under the muff after a period of time. Obviously, that would cause a rough engine when the carb heat is pulled.
That being said, my Cheokee always seemed richer than necessary with the carb heat pulled too but it was like that for the 25 years I owned it.
Mike Berg