petrol in crankcase

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Settled in member
Posts: 59
Joined: Thu Jul 01, 2010 12:16 pm
Bike owned: NC 30, TZR 250
Location: Portsmouth
petrol in crankcase

Post by dirty30-2008 » Sun Feb 03, 2019 9:31 pm

Hi all.
Bike hasn't been used for a couple of years since it last disgraced itself ( broken exhaust valve on No.3). In that time I replaced the valves on that cylinder courtesy of RO, did the carb modification and shimmed the needles.Bike was recently treated to new needle valves and seats, Li-tek seals. Bike was a runner and had light use before laying her up. Although I have started her infrequently I had a problem the other day. She started then clonked. Hydraulic locking up.On removing the plugs cylinder No. 2 was full of petrol/oil mix. Something told me to drain the oil which spewed a highly diluted mix of oil/petrol, over 4.5 litres. Haven't drained it all either as I didn't have a container big enough. My fuel tap in unmodified so no fuel should flow until there is a draw from the engine. For this amount of petrol to bypass /work itself into the crankcase I feel it has to be carburetter related but the tap remaining open?
I can only assume that the valves are not sealing enough when the float level rises. I was meticulous about setting float height to 6.8mm but noticed that that the spring in the new needle valves is stronger than the original needle valves.My first port of call maybe to re-use the old needle valves.
Has anyone had a similar occurrence and did you manage to find the root cause.

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