Engine runs lean, old Webra 61. Who can help?

[Urs Baertschiger]

Many thanks to all who replied.

Del, I run the engine with fresh fuel. 5% nitro, 17% aerosynth oil. For the 
test runs I didn't fit the cowl in order to be able to notice fuel foaming. 
No fuel foaming noticed.
It goes lean right after I open full throttle. Maybe the first second it is 
OK, but can't say for sure as also my hearing needs a second to adjust. I 
checked the temperature by touching the head after the runs. It dosn't seem 
to get too hot.
No significant varnish build-up on piston and head. Barely visible varnish 
on piston.
No, I can't get the engine slobbering rich even with needle valve backed out 
until it almost falls off.

I will check for restrictions in the fuel line once more.


Tony, even though I know this carb rather well and had many of them 
disassembled, reassembled and adjusted many times over the past 20 or so 
years, I will follow your instructions regarding the basic set up. Also I 
will install a new Enya #5. - I don't know anything about the machined con 
rod and the company called "RPM". Where is it located? Somewhere in Europe? 
- We too had problems with the con rod at that time, but as we started using 
bigger props the problem went away. Seemed to be related to high revs.


Karl, I will get the crankshaft out and check the bearings. - I thought 
about this too, but I cannot notice any rough spots or excessive play when I 
turn the crankshaft, neither do I realise any hickups in the air when flying 
the plane. Years ago I always realised while flying when a bearing was due 
for replacement, but this time I can't notice anything unusual. You sure are 
right with your statement, that bad bearings can cause many kinds of 
problems as we too have come to learn over the years. Latest experiences 
gained with the OS 140 RX support these findings.


Again many thanks for the help.

Urs
NSRCA #3069

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