HO360 & PS5 won't cut off at idle

[harleygaz]

Hi. I have an HO360 in my Starduster with PS5 carb. The engine has had 1.5 hrs ground runs since major overhaul and the carb has been inspected and flow tested by Mike's at Tulsa. When I pull to idle at about 500-600rpm and pull mixture to idle cut off the revs drop to about 200 and then surge to about 600 / 700 then drop to 200 and surge again with no sign of stopping (I've let it do that maybe four or five times before switching off at the switch). I tried at 1000 rpm and it cut off dead straight away. I tried again with the throttle cracked just enough to get 800 rpm and it cut off dead straight away. It seems to only do it when the throttle is closed all the way to full idle at 500/600 rpm. Tried with electric pump on and off, no difference. Tried from idle and just a quick pump open and back to idle on the throttle, no difference. Go to rich, ease up to 800, go to cut off and it dies straight away. A&P I know who has worked on helicopters with HO and PS5 is stumped. Any ideas? Cheers, Gary N503CM

 

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