Webra Problems...Some solutions

[Troy Newman]

Gordon,

As everybody is aware I fly the YS motors...but I do have a bunch of
experience with the Webra and the MC carb setup as well as the pro-mix carb
that comes with it. My experience is mostly with the 145 but they are
basically in operation the same motor...The 160 is a little more tolerant on
some things and has better timing and power curve than the 145...

SOOOOO
I will chime in. My personal opinion is you will not see a solution with the
bladder tank. My suggestion to you is to Number #1 turn the pump screw in a
little say 1/4 to 1/2 turn to build more pressure. The next thing is motors
very rarely die rich especially on the low end...They will load up and not
come up but it takes a while to load up enough to die rich...So more pump
pressure is going to actually richen your mixture...Therefore your top end
needle will need to be a little leaner....and the bottom end should be set
as rich as possible...Maybe just to where its almost gurgling in the
middle.....And see what happens. I would get it so rich the motor has a slow
throttle up response...Not and hesitation is LEAN not rich.....Rich is a
slow build of RPM....Lean is a burp or hesitation then a jump to RPM

I'm not being an advocate of the motor, and I'm not telling you its a turd
either....I just know for a fact the bladder tank will most likely not solve
your problem...I think your low end is lean. This is a good case for the MC
carb...as the bottom end can be set rich and the middle can be leaned out. I
know the motors can run well as I have a 145 on a MC carb and it runs
fine....Not as good as my 160DZ for sure...but it will do the job if I had
too. I have not followed close enough to know if you are using an MC carb or
not. My personal opinion is its the way the go if you choose the Webra but
on the other hand its more complex and its not for everyone for sure.

You are welcome to try the tank thing and try this and try that...but in
reality I believe its a setup issue...My experience with the Webra tells me
that your pump may be lean and as a result when things get hot in the
air....you could have some issues...also look at your cooling. Most people
don't cool their motors well at all. Not sure of your model but cooling can
be an issue...I also seem to remember you mentioning that it was eating OS
#F plugs or maybe that was Bill Pritchett's that was eating plugs...The
reason this happens is LEAN. Most often too lean on the idle screw to get a
decent transition without going rich in the middle....This is the problem of
the 2 strokes...Most people adjust the carb...and not there setup....More
nitro helps this problem allows richer idle setting and doesn't go slobbery
in the mid range...also a longer pipe helps this too. Even if you are just
using a muffler make it longer it is tuning to some extend. I'm running
20-30% nitro in my 2 stroke setups...it performs better...not really on the
top end as they already have good top end power and I rarely get into it
that much in a sequence...but the middle responds better. Especially if you
are not on a Mixture control...the nitro helps. MC carb allows you to set
the mixture throughout so if you go lean its operator error and not
carburetor.

Another thing you may look at is tank location especially if the motor goes
lean after an extended idle and you are pushing through a corner...EXAMPLE
the Masters Rev Cuban 8 with 2/4pt rolls from the top....If the motor burps
at the bottom outside radius then it is going LEAN....Now the needle
settings will be perfect everywhere but right there its going lean...Lean
could be on a  stall turn that exits inverted too as you throttle up it
burps lean and dies....The reason:

Many people are very fixated with the Tank on the CG thing...So much so that
they will stick the tank up high in the canopy area where the tank is way
above the centerline of the carb. Then when inverted the tank is low and you
are asking the pump to overcome both the negative G's the low tank and the
acceleration of the model as it climbs...All of these forces are telling the
fuel to stay in the tank....And the pump is gasping for every drop it can
get as the motor is asking for fuel. Combine this with long fuel lines to
get the tank back to the CG and the pump is just overwhelmed in that
situation.

A fix is to lower the tank in the fuse and move it forward. This makes the
fuel lines shorter....Back when we ran pressurized tanks on the YS motors it
was OK to pull fuel from the stab tube...but today even the DZ's in some
outside maneuvers after extended idle will give a burp. To eliminate it I
move my tank a little forward...I have done this for the past few years
since about 2000 and it works fine. The rear of a Tettra 20oz tank touching
the front edge of the wing tube is where mine usually ends up......The
result is a CG shift during flight of about 8mm or about 3/8". You can feel
it from full tank to empty tank...but in the sequence you can't tell it
shifts as I'm only using about 60% of my fuel anyway....The shift for a
sequence is less than 1/8th inch....I have measured it on my scales the way
I do CG and I can't feel it in flying the model.

I tend to run much more forward CG than the average pattern pilot....The
reason I like the model to lock on and track on its own. I also like it to
enter and exit the snaps crisp and clean...A more nose heavy model will do
this very well. Then Spins will suffer a little as the model gets nose
heavy....But in the F3A pattern we have the spins (reversed one that is
harder with a nose heavy model) at the end of the sequence and my CG has
shifted slightly aft from takeoff...So it works for me.

Just some ideas for you to chew on....Look at your fuel lines are they long?
Is the tank well above the centerline of the carb? I don't care if the
engine is pumped or not....If its pumped it allows more latitude but you are
having trouble so go back to basics and start from there.

Just something to look at...

Good Luck and if I can help you out offline please send me an email or give
me a call. I'll be happy to chew the fat with you and maybe we can come up
with some ideas on your setup.

We can talk about props and pipes and all the things that are contributing
to your success of failure running the motor.

Troy Newman
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