The lower petrol-to-oil ratio will make the engine run a bit leaner than normal. This is partly because oil is more viscous than petrol and therefore restricts the fuel flow through the main jet, and partly because there is a bit less petrol in the fuel, and the oil doesn't really burn properly.
I take it you are running the correct spark plug, so you can probably check that it isn't overly lean by inspecting the plug after you have run it under load continuously for perhaps half an hour or so. If it comes up very pale brown, or whitish, it is too lean and you'll have to reduce the oil or you'll damage it. Of course there is no issue at idle, since you have already tuned the idle mixture.
I've already given my opinion on petrol to oil ratios: I like to protect the piston and rings by providing them with enough oil. However with a fixed main jet, to me the risk of cooking the piston through lean mixture isn't worth taking.
