Hi Folks

I have an ASP .91 4-stroke engine swinging a 13x6 prop. I want to know what the ideal idle speed should be, as well as the maximum rpm. I'm new to 4-stroke engines!

Your inputs would be appreciated!

Cheers

G'day Mate,
A 13x6 is too small for a 91 four stroke, try a 13x8 up to a 15x6, your idle speed, is the lowest you can get, & still pick up to full speed without hesitation, of course after it is run in, & the low speed mixture is set.
Top speed is usually no more than 10,000RPM, in the air, so allow about 500 or so revs as the engine unloads.
This is only a ballpark figure, it is not cast in stone, but is a good guide.
Remember, a four stroke will & needs to swing a larger prop than the same size two stroke.
They have much more torque, & will be damaged if they are run too fast, with a prop that is too small, two strokes don't have valves & push rods, to get bent & damaged, four strokes do!

The engine will idle slower with a 15-6 APC prop than it will with a 13-8 wood prop

Hi!
A four stroke engine doesn't have more torque than the same size two stroke actually less! But it delivers its torque at lower rpm!
10000rpm is a good rpm figure to aim for .
13x8, 14x6, 15x4 or 15x6 is the prop sizes that works best for most airplanes ( at sea-level).

I experiment with each 4 stroke engine, I usually put the biggest prop that it will swing while keeping good throttle response. I try to shoot for 8500 rpm on the ground, due to the nature of the 4 stroke I find 10,000 rpm is out of the power range, 9000 in the air is about good. The rule of thumb is over prop it, run it rich and it hasn't failed me yet. try a 15-6 or 8 use a techometer if your still over 9000 rpm then maybe try a 16-6 or 8 or bigger if it wil turn it ok.

Thanks for the responses! It's much appreciated!