I have a C85-12F with Stromberg Carb and Bendix mags that keeps backfiring when throttling off to idle (Aircraft is in restauration so only ground runs have been made as of yet).
After shutting down the engine it is obvious that the #3 cylinder is much cooler than the other three.
Idle is otherwise smooth but over 2000 RPM sometimes there is a sudden spike in RPM as if the #3 cylinder start operating normally and then it falls back.

I have checked the following:

- The valve seems to be ok and is not stuck
- Compression is ok
- Mags are ok
- Carb mixture setting is ok
- spark plugs swapped but no improvement

For some reasons it seems that it runs better with Carb heat on.
Any suggestions for next steps in this trouble shooting?

All and any help is appreciated!
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192 is in the mail to you. Hopefully I can have the new website up in the next few days and it will be much more useful and friendlier to use.
-john-
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Clyde, also known as "The Cub Doctor" probably has the Piper drawings for placement of the inspection rings. I know that they are available for other Piper models.
Bill
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John, your post about Cub Clues 192 below was seven months ago and 92 hasn't been sent to me. My last one was No 191 published in April 2018. My set is otherwise complete.

Please send 192 to Donald G Henderson
P O Box 909
Bedford IN 47421-0909

Thanks.
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Hi. I have started covering my J4A following a very long rebuild. I am looking for drawings to show the location of the access holes. Pictures of a covered wing would be ok as well.
Thanks
Roger
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I am covering the wings on my J4. Where would I find details for the inspection holes.
Thanks
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Does anyone know what years or which L-4 models that had the Wind driven Generator (General Armature AG-40) installed as standard?
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Thank you John.
I thought Jim might have finished his by now. I did visit him a couple of time when I was with friends in Denver. I have also been in touch with Roger Pepperell, who has given me some help. I just need to decide the best way to get from NY to Lock Haven.
Happy Xmas.
Thanks again
Roger
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There are usually at least two or three J4s in attendance at Lock Haven. Dan Fogle is one and another one or two are usually there. I can get you in touch with Dan if you would like. Jim Dyer of Univair is restoring a J4. He will be there and is a good source of information.

Merry Christmas,
-john-
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Hi All
I am planning to finally make the trip across the pond to Lock Haven for the Sentimental Journey 2019, via New York for the wife of course. The main reason is to gather information so that I can complete my J4A cub coupe. Originally N26198 now G-AFZA. She was damaged in a ground accident 12th April 2002. Not me!
So if there are any J4's intending to fly in then I would very much like to meet up. I need a close look at the windscreen installation and door frame trims mainly. I did not get hold of the aircraft in a complete state. It had been extensively dismantled by the time it got to me with parts missing.
Also if there are any members in the Lock Haven area, please feel free to get in touch as local knowledge would be very helpful.
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We are working on it. I can send you a 337 for one to model until then. Model is the 6131.
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Absolutely! I was able to find the babcock stc you are speaking of. I've looked for months for information on both of these issues and haven't found a whole lot of info for either. It seems this stc covers the swap plus allows the gw increase after required mods. Can't thank you enough.
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Wow! A real barn find. As I understand it, the gross weight increase for some of the early Cubs involves replacing the landing gear fittings with the later version. May be more complicated than that but certainly something that is better done while the fabric is removed.
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My j3 has not had a gw increase yet. It seems to have been stored in a barn since 1954.
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You may already have this, but "The Cub Doctor" can provide you your airplane's original build sheet for a small fee. He will probably also be a good source for current and specific paint color numbers. He restored an award winning PA12 himself.
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According to things I have read, the Babcock STC covers converting the J3L to use a Continental A65. However, there appears to be a procedure established by Piper for converting a J3L to a J3C, which would then allow use of any of the engines listed in the TCDS for the J3C. A related question would be, has your Cub been approved for the gross weight increase to 1220 lbs? It is a separate issue but worth considering, especially if you have the fuselage fabric removed.
Good Luck with your Cub!
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Where would I look to find information about the purchase of the stc to convert a j3l to use any engine on the a691 continental tc?
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Hi Dell.
I don't know if there is a S.T.C.for the API tailwheel but I have a very detailed field approval for my J-3. I can send a copy to you if you want it. It should be easy to get it approved on your Cub. Call me at 231-499-3974

Don
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I have the paint scheme layout drawing. I am looking for the original colors for the PA-12. Any help would be appreciated.
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