Well team, after 12 or more hours misfire-free I feel confident enough to
announce that I have (finally) found my misfire. It was not the throttle
linkages or the throttle box.
When my co-builder (now deceased) Nigel put the fuel pipes in for the carbs
he used the #2 fuel pipe from Europa, rubber with a stainless steel
braiding. He connected pipe to the carb banjos and ran the pipe under the
carb to the standard t-pieces mounted on the engine mounting cross member.
He insulated the pipe with "air conditioning" type insulation (a better
quality than "central heating" insulation.
The pipe (with insulation) ran approximately 1 1/2 inches from the exhaust
manifold.
During our very hot summer last year (100 degrees !) the insulation "melted"
on this most critical piece of the fuel pipe - nearest to the exhaust
manifold [on the starboard side where the air has more restrictions to its
flow because of the oil dry sump tank]
This heated the stainless steel which promptly conducted the heat up
UNDERNEATH the insulation, so negating the insulation !
In the climb the fuel was flowing quickly enough to avoid any vapourization
problems, but when I buttoned off in the cruise at the top of the climb -
lower fuel flow - vapourization - misfire; which would normally go away (as
things cooled down).
So each change last autumn/winter which seemed to improve/fix it was just
the cooler weather. It was fine in Feb and Mar and came back in April when
the temps went up.
The pipe has now been changed to the #3 pipe (which is rubber with an
insert, no braiding) (#1 pipe had blue cotton braiding) and the pipe goes
OVER the carb. I have no insulation on it and I have had no trouble
whatsoever in temps up to 27 Celsius since.
I feel pretty stupid about all my previous "fixes" but I am positive now
that I have really done it. There was an obvious bit of melted insulation
near the exhaust manifold which was hidden and only some lateral thinking
and a grope under there brought it to light.
I am planning replacement of all the s/s braided pipe and some blue braided
pipe with the #3 pipe. Unfortunately I don't have enough and my recent (last
6 weeks) orders to EMIL have not produced any pipe, for the obvious reasons
:-( I only asked for them to contact me for my cc number and didn't send
them a cheque. So my priority will be to replace the blue braided stuff in
the tunnel as it is very petrol-smelly whenever I open up after a night in
the hanger. There is no smell in use, ground or in the air.
Of course this might all be another optimistic failure, but as I say I have
done 12 hours at least with it in the current state.
One day I will get to a fly-in, I have much more confidence in it now !
Richard
Richard F.W. Holder 01279 842804 (POTS)
Bell House, Bell Lane, 01279 842942 (fax)
Widford, Ware, Herts, 07860 367423 (mobile)
SG12 8SH email : rholder@avnet.co.uk
Europa Classic Tri-gear : G-OWWW, High Cross
PA-28-181 : Piper Archer : G-JANA, EGSG (Stapleford)
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