Carosel43

Now

lucky for you I was able to get out today and fire up my 150. I deliberately put the needles very rich to represent an engine that's had some basic settings applied. in this case it was about 6 turns on the slow run and 3 on the main (other engines will have different basic settings).

Anyway I fired it up and set the top end as before (lean off pretty quickly until close and then slowly to the max), then I throttle back and there are clues about the bottom end tuning. For a start its very lumpy, lots of smoke and is not really that happy below 2500rpm. The rpm also dances around and throttle response is poor.

so, I lean out the slow run in quite large 1/3 turn chunks and check the pickup as I go. Eventually the engine bogs and wont accelerate. That means im too lean. Other clues for a lean slow run include a fast but smooth rpm that dies abruptly if throttled back further in an attempt to drop the rpm, difficulty starting (the engine picks up on the prime and then stops or just pops and farts when driven by a starter), excessive throttle opening to allow starting.

from the lean setting I slowly open the needle in much smaller 1/8 turn increments until im really close, then its down to really small 1/32 tweaks to get it perfect (you don't have to be that anal if you don't want to). I then reset the high speed needle as the slow run has an effect on it.

When correctly tuned the throttle response is much better, idle rpm slower and smotherthe whole engine is more reliable and there is less smoke blowing about.

http://www.youtube.com/watch?v=DaeLy...ature=youtu.be

Enjoy

p.s. I also have another video of a twin and I set the slow runs on that as well. Its a part work as the engine stopped twice and needed to be restarted. As its not strictly relevant here I wont post it unless there is significant interest. if anyone wants it for their own personal use let me know and I will send it over (after I knit it together)

And yes I know my test bench is filthy and my prop has chunks out of it, but that's my benchmark prop and the state of the bench matters not as the pipes are nice and clean!