KeysFox
Joined: 05 Jan 2009
Posts: 137
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 Posted: Fri Sep 09, 2016 4:57 pm Post subject: RotaxEngines-List Digest: 5 Msgs - 09/07/16 |
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John, I hesitated to mention this because I had rough running issues at
high idle only after carb overhaul but not above high idle rpm. However
the principle seems to be the same for idle jet or larger jet. In essence
I got the same recommendation to blow out the idle jets from Lockwood,
including the comment that you may not see anything but blowing out the
jets is a typical first step with rough engine operation at the upper end
of idle range because fuel flow thru a very small jet with an undetected
restriction causes rough running at high idle before the next jet cuts in.
If the engine runs smoother when rpm is in the next jet operation range
then stick with blowing out the idle jet only.
Note that float bowls have a tendency to not seat perfectly allowing a
small amount of air to be sucked in during engine running which can result
in rough engine running too. Check for any fuel dampness under the float
bowl which would be an indication of a gasket leaking air in during
operation and maybe letting just a bit of fuel out when the engine is
stopped.
There have been gasket changes between float bowl and Bing carb housing
over the years. Some thicker gaskets than others ,,so it was suggested
that the thicker ones may seal better.
Note that rough operation can cause float needle valve to vibrate and
allow minor "flooding" possibly with evidence of fuel at the carb air
intake opening.
By the way I had my carbs overhauled the first time because they were many
years past the recommended time in service between overhauls and took the
plane immediately in its trailer to another state.The roughness showed up
right away so I ended up at another Rotax shop for another set of carb
overhauls including boil out of carb body. VERY shortly thereafter the
roughness returned. The second shop foreman suggested that I blow out the
idle jets. It seemed to work. My wings have been off for recover since
then so I have to be a bit guarded about that observation.
I also installed an extra fine gascolator screen as suggested by a Rotax
training guru at the second shop.
Oh, in case you my be wondering, the finger strainers in the fuel tank
pickups were clean as a whistle and the inline glass tube style filter
elements were clean as a whistle throughout all of this and I use a funnel
with a fine mesh screen to pass fuel into the gas tanks when fueling the
plane. However between overhauls I did change out the gas lines which were
well beyond the five year in service limit called for by Rotax.
OK enough rambling.
BJ Kitfox IV 1050, Rotax 912 80 hp.
| Quote: |
<jelling(at)newmexico.com>
All, I had exactly the same symptoms years ago. I cleaned the carb
ports and it went away. On both carbs the main port and the idle port
looked PERFECTLY CLEAN when I took the carbs off but nonetheless the
problem went away when I blew them out.
A helpful mechanic at LEAF directed me down this solution path, by the
way. He even predicted that I would not see the obstruction in the ports.
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B Jones
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