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

[Nedim Bek]

Urs,

We used Webra 61 Racing and Longstroke engines for many years at 80's. I
certainly agree Tony's comments about the Dynamix carburetor adjustment. We
had same problems for many times. The problem can be related to the
carburetor; the position of the brass metering tube (or bar) is very
important, also after several hundred flights this brass metering assembly
wears out, and fuel starts to leak between the bar and the sleeve, this
causes the engine to run lean. Dynamix carb can not suck fuel by itself and
needs the Perry pump provided by Webra for this engine or other means of
pressurized fuel supply. Most of the time the pump is the reason of the
problem. Either the pump membrane gets hard after excessive use or the
copper-beryllium valves inside the pump fail. I saw cases that those cross
shaped thin valves cracked or even punched out. You can test the pump by
turning the crankshaft and watch the fuel pumped. Every turn must pump about
one or two drops of fuel.
Check the carburetor fuel metering assembly. If the problem persists chance
the pump. I don't recommend to run the engine on exhaust pressure without
the pump, it never worked good for me.
Hope this will help!

Nedim

----- Original Message ----- 
From: "Del Rykert" <drykert at rochester.rr.com>
To: <discussion at nsrca.org>
Sent: Saturday, November 29, 2003 12:43 PM
Subject: Re: Engine runs lean, old Webra 61. Who can help?


> Hi Urs..
>      Being you can't richen your engine you definitely need to address
that
> part of the feeding problem. Removing pump from equation if tank is long
run
> to carb unless you raise tank above midline is only going to worsen you
lack
> of fuel. Do you have a engine stand to test in stand? I would do what Tony
> suggested and then if that doesn't fix it try running on stand. I assume
you
> are using large enough diam. tubing to fuel carb. Don't mean to sound
> insulting just trying all ideas of what might contribute to your dilemma.
>     Please let us know how it goes.
>
>      Del K. Rykert
>      AMA - 8928
>      NSRCA - 473
>      Kb2joi - General
>
>
> ----- Original Message ----- 
> From: "Urs Baertschiger" <ursbaertschiger at hotmail.com>
> To: <discussion at nsrca.org>
> Sent: Saturday, November 29, 2003 2:22 AM
> Subject: Re: Engine runs lean, old Webra 61. Who can help?
>
>
> | 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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