The most common problem I see with 4-stroke engines, especially with planes that are stupid overpowered, is getting the engine's idle rpm slow enough to not taxi the plane on pavement. Four strokes have a hard time matching a 2-stroke's low idle rpm because they fire every other revolution and thus the glow plug has more time to cool off between firings. Also, when the throttle is closed, four-strokes have a very low effective compression ratio because the cylinder is only partially filled (a vacuum in other words) with air/fuel mix when the intake valve closes and the piston has to travel quite a ways up before the air in the cylinder is at atmospheric pressure and the compression can start.
Some people use an on-board glow igniter to solve the problem but the real key is to have the idle mixture perfect. Most everybody knows how to adjust the high speed needle but a lot of experienced flyers seem to be absolutely clueless about adjusting the low end and just live with thirsty planes that need "wing walkers" to hold them back before takeoff.
If you power it like a scale airplane, you can get away with an idle rpm that is 1/4 of the full throttle rpm. If you power it for ballistic verticle at full throttle, your idle needs to be 1/5 of the full throttle rpm or slower or you will need someone to hold the plane back for you on takeoff and will only be able to land by killing the engine.
Saitos come with the low speed needle set very rich. It should be left that way for the first couple of engine runs. The engine will be extremely thirsty at part throttle and the fuel tank will be empty in a matter of minutes. As you break in the engine, you need to gradually lean out the low end. If the idling engine revs up when you pinch the fuel line, your low speed needle is too rich.