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John, I had similar experience with a 65hp powered pietenpol and the problem in my case was the large fuel filter that had been installed on the firewall. Initial take off was OK as cooling adequate in the fuel supply behind the engine but that area heated up enough to cause the "large supply" of fuel slowly moving through the filter and line to Carb to form bubbles and interrupt smooth flow of [auto gas ] Once things cooled some the problem vanished. Auto gas RVP [Reid Vapour Pressure] varies greatly during the year from about 7psi RVP during summer to about 11 or 12 during winter as more C4's are added to assist engine starting.
Can u direct more cooling air to the fuel ? Can u climb at a faster rate to get more cooling? How are the engine baffles? Pay attention to all that engine heat during climb out.
Ron Hynes Alberta Canada
-------Original Message-------
Date: 12/27/05 06:53:57
Subject: [COUPERS-TECH] engine knock?
What do you think is causing this:
" Normal climb to any altitude, full throttle, wired rich, sea level
area. Level off, leave at full power until speed increases to cruise,
as the RPM builds to 2500, the engine starts to "knock" . engine
shakes. Throttle back to 2300 wait a minute or so then you can advance
the throttle to 2450-2500 and it's smooth. Won't happen again til the
next t/o and climb. Won't do it on climb from one altitude to another.
Has auto STC but hasn't been run on auto fuel for at least the last 50
hours. Has this problem on 100LL
Had sticky valve at one time in it's life but cured at the shop.
Front right cyl. engine about 1000 SMOH
Suggestions PLEASE!
Thanks
jsilberman
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