The International Cessna^® 170 Association

I didn't find anything saying it existed before the rebuild. Did I miss something?

George... have you actually removed the spark plug leads and observed them to discharge a spark with the engine idling? (If so, have you done it again with them hooked up to the removed spark plugs to see if they are fireing?) Have you tried swapping the spark plugs to a different cylinder to see if the problem follows? Have you had the ignition leads tested with a high-tension tester?
I am suspicious of the ignition, personally. Dual ignition systems do not always preclude failures occuring in ignition in the same cylinder.

Intake leaks can also be trouble-shot by pressurizing the intake with a vacuum cleaner exhaust and painting the system with soapy solution to look for bubbles.

SloPoke,
You've spent too much time fooling with those Lycoming engines. You'd need a six point EGT on a Continental on a C-170!

Yep - but it was on the 0200 in my racer that I was thinking. I never could get much past 2 anyway.
cg

Answer in regards to leads and plugs, Yes I did undo the leads and spin the engine over. Spark was there. Also removed plugs and hooked up to wires. Spark was there. Have received some good tips that I will look into. We just got dumped on again here in North Ohio so it will be a bit until I can get back at it. Thanks again all. Will report out when time. George

A tool we use here at the shop for checking vacuum leaks and intake leaks is an EVAP tester/Smoke machine. This puts an inert smoke under low pressure in the system and helps locate those pesty leaks. It's helped us locate those hard to find intake leaks that are buried in the deepest recesses of an automobile engine compartment . If you know someone that has one, this may help you determine if you have an intake leak.

Paul

and now for the rest of the story............

Weather finally broke and allowed me to tackle this issue again. Is finally fixed. If you recall in early posts, I did check for intake leaks. Found none although it had all the symptoms of one. I pulled the cylinder assy off with the cast elbow still in place. I checked the elbow over carefully for any porosity or wear from the front baffle. None. I decided to put my mouth up to it and blow in it. It leaked from the gasket area on the back side where I could not check for leaks very well. Removed the elbow and put a straight edge over it. Not quite flat. Trued it up with sandpaper and oil on a flat plate. Replaced with a new gasket. Also replaced the fuel nozzle on the carb as recommended when using a one piece venturi (venturi done years ago by pervious owner). runs smooth now across the RPM range. Thanks all for input.

George

Long haul, wasn't it.

Thanks for posting the resolution. Glad you got it fixed.

blueldr, you aren't kidding, it sure was a long haul. Should also metion that this final problem was masked early on with an ignition problem. Nicked p-lead causing an occasional grounding. Hope to enjoy the thing now. Next problem is son number one wants wants a key now.......

George,
Do you mean that he didn't want a key until it WAS fixed?

gwillford-
It's amazing how much difference a tiny intake leak can make. I had the same thing happen right after overhaul, the engine was smooth as silk at cruise but loped at idle. It was 75 hours after the o/h with another IA doing the annual before the leak was located at the cylinder intake flange gasket. Now it idles as smooth as it cruises.