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To much oil cause a bad/non idle?

typhoon

Regular Contributor
I rebuilt my Mariner 60 twin and it's been running on a really oily mix, around 35 to 1. It needs choke to start and won't come down to a nice slowish idle. It sort of comes down, then starts to slowly falter, then dies over a course of 10 seconds or so.
The idle mix screws definitely affect the idle, I can screw them in or out and cause it to run rough, they're set at best idle.
Engine is synched as per manuals and all checks out there.
So, will a really oil rich mix cause an issue like this?
 
Why was the motor rebuilt ??-----------If it was a sudden failure did you fix the cause of the failure ??-----------Slowly dying may mean internal leaks ( crankcase compression ) and may involve seals.-----If equipped with a thermostat was it checked / tested ??
 
Thanks for the reply. Teh engine was old and had glazed the bores. I rebuilt it with new rings, a light hone and all new gaskets/sealant etc in the powerhead. Reeds looked excellent. It's SO close to idling, it just won't quite get there. It only dies when the idle gets down to where it should, just above where it starts dying (fast idle, say 1200 rpm) it runs flawlessly. Thermostat is new and pressure bypass also works/was checked. Assume the powerhead is completely fresh, everything was checked and was O.K/replaced if needed.
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