Hi All,
I flew yesterday for the first time since investigating the rough running at mid
throttle settings on my 912, 80 hp Rotax, with Arplast / Mark Burton constant
speed prop.
I said I would report the results, the suggestions I received from the forum and
the action I took as a result.
I am pleased to say I had three flights totalling 2hr 35 mins without a single
hiccup.
The suggestions I received from the forum and the action I took as a result:
1) Re new the spark plugs and check the HT leads for
break-down...............My
plugs were 130hrs since last renewal, so I replaced them. The HT leads are
the original ones (c.1995) so I cleaned them (one was a bit oily) and will
replace
them if the problem returns.
2) Clean all the jets in the carbs.............I stripped the carbs
completely,
washed with acetone and blew all cavities and jets with compressed air. I
found a small slither of silicone in one of the needle jets.
3) Check for air leaks.................I cleaned and inspected the rubber carb
mounts and found to be OK, I checked the plastic tubes from the float chambers
to the air intake plennums which were OK, I inspected the balance tube
connections
which were OK, but I found the MAP (manifold air press) pipe which was
rubber, had perished at the take-off nipple, so I replaced the pipe with a
plastic
one.
4) Check that the jets and needles are properly located................My jets
were all screwed in tightly, but both "O" rings on the starting carb jets were
broken, so I replaced them. Both needles were located on the second notch
---From the top. Is this the correct position - has anyone else checked theirs?
5) Try raising the needles by one notch. This solved a similar problem on a
914...............I
appreciate the philosophy and I will try this if the problem
returns.
6) Check for splits in the fuel lines..................Mine appear to be OK.
7) Check for splits in the diaphragms.................Mine appear to be in
good
condition.
8) Check for low CHTs.......................My coolant temperatures have been
running at between 85 and 100*C
9) Check for carb icing.......................My carb temps were over 20*C
when
I had the problem.
10) Monitor EGTs on all four cylinders, because readings would indicate
whether
the mixture was too lean or too rich..........................I agree and I
would like to monitor EGTs on at least both rear cylinders, but I don't have
any at present.
11) Make sure that the carbs are properly balanced...................I balance
mine regularly with a pair of vacuum gauges.
My problem could have been caused by one or more of: the slither of silicone,
the
MAP air leak, the broken "O" rings, or the 130 hr plugs (although I normally
replace spark plugs @ 150 hrs as recommended). Time will tell, no doubt, if
the problem returns.
I hope my experience might be helpful to anyone with a similar problem, or for
planned maintenance purposes.
Once again, many thanks to all those who offered their suggestions.
Best wishes,
William
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