Originally Posted by tigreflyer
Give me a good running Fox 35, McCoy 35 or 40, any variations or an OS 35 S and I'll have that puppy doing the 4 2 4 before you know it. The little experience I've had attempting engines not designed to do the classic CL break to break well proved an exercise in futility.
I disagree a litle bit here.
Most motors will 424 but some are happy 424 at one rpm range others at a different rpm rang, because of their particular timing and porting, you just have to find that happy place and go there. Rpm is not important, the motor run is important. First focus on the motor run, then you focus on speed. If you want to adjust speed you change the pitch of the prop and or diameter not the needle valve.
On the ground run the motor and put the nose up and see if it 424 reliably. That should be somewhere a little below the max rpm use your ears for this and get used to this sound.
In flight notice what the motor does in a loop. If it goes in 2 and does not cycle back to 4 then you do not have enough prop load or it is getting too hot and it has not sufficient cooling. In that case use a larger diameter or heavier prop add oil in the fuel. If it struggles to go 2 and wants to stay in the 4 then the prop has too much diameter or weight use a lighter one (do not take away oil).
When it goes 2 watch what the motor does. Does it scream like mad or it is braking in 2 with authority but not harsh. This is a top rpm issue and it is fixed by the venutri size. Venutri size is like the gas pedal on your car the more you press it the more the air intake opens and allows more air flowing and the motor revs up. So if your motor is too harsh then get another venutri with a smaller hole or steal your wife’s stalking and an O ring and put a few layers on the air intake to restrict the air (this is a good way to create an air filter).
Another way to fine tune this is with fuel. Take away nitro to soften the run. This will not be a drastic change but is more subtle it should be done towards the end of the motor tuning and it can be very useful during travel. When you go fly at higher altitude or lower altitude. Higher altitude requires more nitro because nitro is oxygen. If you go to the NATS at higher altitude almost everyone will go 5-10% more nitro compared to what they are used too and perhaps from 2 to a 3 blade prop too.
I guess you need to know what to do and what direction to take compare to your flying stile likes and dislikes and tune to suit it. Whatever you do keep that motor in the happy place the needle helps a bit but it is not to be abused and the motor must be kept in the sweet spot. I hope I did not bore you to death.