Thumper1

I know this is like asking how high is up, but here goes;
How much cranking compression is a 1.2 AC supposed to have? I have a brand new one that doesn't seem to have a lot. So far, after about 12 flights on 20-20 fuel, I can easily start it with a starter/battery that I use for my .40 size planes. That starter will not even begin to turn over my Saito 1.5. The engine turns a 16-8 APC about 9200.
Thanks
Bill

flyn2high

My Feedback: (2)

Hi Bill:

It sounds like you have plenty of power, Going by the suggestions at [link=http://www.probuild-uk.co.uk/factsheets/ys_engines.php]PROBUILD[/link] they say that the 120 AC will get a max rpm of 9000 with a 15-13, 15-12, 15-11. If you take the middle one of 15-12 I calculate the hp at 3.16. With your 16-8 at 9,200 rpm the hp is 2.9 which is practically the same. I have a YS91 AC and I can also start it with my 40 size strarter. The 4 stokes need to allow some of the combustion gasses get by the piston for lubrication of the crankcase. I think you are probably OK and your Saito may be very tight. However, I have no experance with a Sato. Have you checked the valve clearance? I think they reccomend 1.5 to 4 thousands of an inch clearance cold.

Lou

Dave Shadel

If it turns the prop at that rpm, it sounds like it's OK. Try adjusting both the valves to .003" and see what happens.

Mykol

My Feedback: (1)

I have the same 120ac engine and prop. (carbon fiber)
I bought it rebuilt a few weeks ago and I'm still tweaking its performance.
Question: I have mine leaned to about 9400 rpm with that prop. Any richer and I find that the acceleration up to max power is incredibly slow...in the area of 15seconds to accelerate from idle with a 1 second throttle up to full. Is this normal?? What is the max rpm, I thought it was 9000?
Furthermore the idle tends to wind down to a stop after about 30-40 seconds of idling. I've given the reg some turns in to lean which is what I've read would be required but it didn't seem to help the idle. Other than that I'm happy with the engine.
It's in a Funtana90. I thought it would have more vertical power even with the Coolpower 25% I've tried. It is just able to pull out of a torque rool vertically. So I've gone back to 15% coolpower because the powerloss is bareable but the price per gallon is.
Any suggestions or thoughts?

Dave Shadel

You probably need to drill the airbleed in the carb barrel to 1/8" It will help and you'll be able the richen the reg up to where it should be.

When the weather cools off your 15% probably won't cut it anymore.