Hi all you 4 stroke and saito guys. Got a saito 100 with just over a gallon thru it that I flew for the first time today. I'm curious about the idle being so high and wonder if anyone has any advice that might help me get it lower. I know every engine is different and if mine will settle in after a few gallons I'll just consider it so and do nothing but I'm thinking I still may not have it tuned in properly yet. I'm using powermaster 20/20 at the moment. Probably will have to go to wildcat or byrons after the powermaster runs out since I've heard they're out of business. But anyway prop is s zinger 14X8. Max rpm about 8700 and idle is about 2300. It will idle lower at about 1850 or so but not reliably. I'm wondering if this is normal? My HSN is about 1 3/4 out and the LSN is about 3 1/2 turns out. Plane by the way is the Aeroworks Yak 54, 60 size. I've never had an engine before that idled so fast that I have to worry about chasing it around the runway (paved). Again, if this is normal OK, but if anyone thinks there's something I can do at this point to get the idle down and still have a good transition, I sure would appreciate the advice.

Shaggy
Loving the YAK!

It's still probably way rich on the bottom end. They come that way to ensure a sloppy rich break in. Continue leaning the bottom end out as it breaks in. When you get it too lean it will idle great like a sewing maching but then will die when you hit the trottle hard. At that point compromise and richen it up just a bit to retain the transition to full throttle without dying. As it breaks in even more you may be able to lean out the bottom end a bit more.

If you want to know where you are at in a hurry now, pinch the line to the carb while it is idling. If it speeds up considerable then you are still way too rich!

Ernie

2200 - 2300 is about as low as my 100 would idle reliably even after broken in and well adjusted with 14/8 apc.

Okay thanks guys. I did try pinching at idle. No rpm increase. So it may be as lean as im going to get it for now. Someone at my field suggested a heavier prop. What do you think?

A 15/6 apc will help a little, maybe 200 to 400 rpm and your YAK may like it better

Denis

http://www.hobby-lobby.com/13.5x8_pr...QueryId=630799

This Graupner 13.5x8 or its sister the 14x7 will either one give you a better idle than you're getting, the 14x7 would be a better choice if your plane is landing hot. Your idle should easily be 2,000 or less. I like to set mine up for about 1,800 then use 2,000 as the real idle.

Pinching the fuel-line at idle; if the mixture is set richer than normal, will momentarily raise the RPM...

However, if does not constitute a "pinch test"; as it applies to a two-stroke engine...


In a four-stroke, the crankcase does not participate in fuel induction and thus fuel cannot pool in it; like it can in a two-stroke...

Pinching the fuel-line does, however, lean the mixture momentarily, causing the ignition to occur sooner and the burn to reach maximum pressure sooner...
This causes the RPM to increase momentarily.


This idle RPM is pretty close to the bottom line.
My Saito .72 cannot idle any lower either.

Saito engines have a pretty hot cam, which like in full-size engines, keeps the idle elevated...
With just one cylinder, this engine cannot really have 'lope' and will simply shut-down, if you try.


A YS will idle lower, because its forced induction allows getting good power with milder cam timing, so it can easily maintain a 2,000 RPM idle, but only on a more expensive fuel...

EDIT: Closure.

Dar, that's why I don't waste my time using the pinch test on fourstrokes. I also make any changes to the needles slowly and in small steps. I don't care what anyone says, fourstrokes don't respond instantly to needle changes, I'll bet you've discovered the same.

Quote:

ORIGINAL: Hobbsy

Four-strokes don't respond instantly to needle changes, I'll bet you've discovered the same.

Sure I did, David.

Since we're at tach readings I will share my saito 100 rpms...

mas 14x7 3blade with 15% omega @8900rpm
with 14x8 apc 9400rpm with the same fuel.

Yup - same engine, prop - exact same rpm for me too. Nice to see ledgers balance like that!

With the APC 14 x 8, my Saito idled at a uncannily smooth 1800 rpm. My YSs both idle slowly but have a distinctive "8 stroke" beat to them.