Kevin, I use 15% Bryons Heli fuel( no longer available). I add about 3 ounces of Castor. I use the stock Venturi. I run it on the ground adjusting until it quits cycling back and forth 2-4 then just slightly richer to launch. This is on a muffler for SE or header muffler for RE. If you want it will slightly break in some maneuvers. If you don't like that adjust slightly ( very slightly) richer and it will mostly run in a 4 cycle. I use about 5 ounces of fuel for the pattern .
We are at 1,400 feet elevation, it will use more lower altitude. I will try Powermaster 15% Heli fuel soon, it has 23% Oil all low viscosity synthetic.
The 67 runs much better with the 15% and is easier to needle. I believe you have the same prop I have ( Brian Eather 12.5x5.3) three blade slightly under camber etc. You can take some pitch out to slow lap time down or add a little it needed. Due to the long stroke of this engine it does not wind up to much if you keep the pitch down. Mine does not break into a 2 cycle much when I get it right just beeps occasionally on some maneuvers.
When I say set it richer I am taking about very, very small needle adjustments 1/16 inch or so at a time until you get what you want .
The key for me has been letting it run on the ground until it warms up a bit then making sure it does not break into a 2 cycle or any hint of it on the ground then set it just slightly richer past that. ( How much richer depends on you) Hope this helps. A Fellow flying buddy is using a RO Jett 76
RE using same fuel same adjustment etc runs the same as my 67 . Plane is 68 ounces hauls it fine. Not sure how many head gaskets as it has been a long time since I changed anything it runs so consistent I don't mess with it.