Hi all - I am new (only a little over a full year) and have gone from my LT-40 with an OS46 FX in it to my SIG 4 Star 60 with a SAITO 91.

The other day at the field I was told that the blend of 80% Castor to 20% Synthetic could be bad on my 4 stroke and make the exhaust valves stick after awhile. I was then shown the brown crude building up around the exhaust on the muffler. I thought this was normal for a little discoloration to start showing up.

Suggestion was that I go to an all synthetic fuel. What are everyone's thought's on this.

Also suggested I could drop to a 10% from 15% nitro and then only have one fuel for both engines.?

I don't know enough about it yet to tell the difference. I have 2 more gallons to go through before I need to buy more.

Thanks for any advise you can give me.