skrez

My Feedback: (15)

Hi Guys,
I have a new Saitio 100 in a h9 Spit that has run great the 1st few tanks. Last couple times I took her out it seems the idle has been very fussy. When I try to idle under 2000 rpms, it will run for a while and then cut out. I think I`m close on the idle, when I richen a little and take the glow driver off I can hear a slight change in the idle. I have been using the same fuel, 15% nitro and 18% oil Omenga. I do not beleive the motor is fully broken in yet, it was ran on the bench for about 45 minutes, then about 6 tanks in the air. Also, I have to mention the last couple times I went flying it has been 90f + degrees. Any suggestions ?
Regards,
Frank

w8ye

My Feedback: (16)

The 100 is more reliable with an idle in the 2300 to 2400 rpm range

Harry Lagman

Frank, I run a Saito 100 in a H9 P51 (inverted, with a similarly positioned tank). With this setup, my idle was a very reliable 1800 rpm, running either 15/18 Omega or 20/20 Coolpower fuel and an OS Type F plug.

Once your engine is broken in to your satisfaction, I would recommend checking the tappet clearance, trying a fresh glowplug and fresh fuel (your 15/18 mix should be fine) to establish a baseline. Then, try leaning off the low speed needle as much as you can while still retaining the ability to transition at a normal rate to full throttle from idle. I run mine absolutely as lean on the idle as I can get it before transition suffers.

An additional hour or two's running generally will improve the engine's behaviour somewhat.

Good luck.

skrez

My Feedback: (15)

Thanks Harry,
When the idle is too low will the engine die when you transition from low to high?
Frank

Harry Lagman

Frank, it's possible that with a very low idle speed if you really crank the throttle on quickly (rather than easing it up) that even with a good idle mixture, you could end up with a "fire out" situation. Raising the idle speed would help in this situation.

Certainly, if the idle is too lean it will die when throttled on quickly. A richer idle setting would be the fix for this.

I would aim for a reliable idle of between 2000 and 2200 rpm initially and lower this once she's got a couple more hours up if you so desire. Your Spit should land easily even with a 2200 rpm idle (I assume you've got a 14 x 8 or 15 x 6 or similar prop on it). My P51 always seems to need a bit of throttle on approach when landing.

skrez

My Feedback: (15)

Thanks Harry, I`m using a APC 14x8
Frank

scratchonly

You can lean the idle too much, negating the the hi speed needle's ability to richen the engine, so be carefull.

Runway

Lots of good advice for you in these answers,skrez.

Can I just add that it is usually better [in my own experience] to set the idle screw on a four-stroke to allow a good transition from low revs to high as a target, rather than have any given rpm level in mind for the idle.

Once your transition is set, the resulting rpm is 'what you get with this particular engine at this particular stage in its life'. The idle rpm usually improves with time [i.e. becomes lower] as Saitos take quite a while to 'run in'. Periodic resetting of both upper and lower carb. needles is recommended during this time. Impatience can result in running too lean - sometimes with expensive results.

Once run in properly, you may find, also, that a fairly high level of nitro is needed to give the lowest idle prm for a given good transition.

I've also found that my four strokes [once they are run-in] seem to run better with fuel containing oil around the 15% level rather than the 18% to 20% some people use.

Good luck - the Saito 100 is a lovely engine!