Let me see if I understand this correctly. It idles great when it has power, but dies when you remove it? Assuming the glow plug is good, this usually means you've got the idle set too rich. How does it do at full throttle with the power removed?

Here's a quick guide to setting the needle.

You should always set the high speed needle first. Only after you have this correct should you begin to work on the low speed needle.

Setting the high speed needle on a 4 stroke requires a bit more care than on a 2 stroke because the change in tone as it goes from slightly rich to peak and then lean is less obvious. However, the difference can be heard. If necessary, use a tachometer as a visual guide. I always set my high speed needle slightly rich. Once I've got it where I think it's right, I point the nose of the plane straight up. If the engine starts to sag, it's way too lean. Lower it and richen the high speed needle. If it keeps the same speed, I consider it a bit too lean still, so I richen it a bit and try again. If the speed increases a bit when I first raise the nose, but then stays steady for 10-15 seconds, I consider it good to go. And finally, if there's a big increase in speed when I first raise the nose, it's probably richer than it needs to be.

After you've got the high speed needle set, it's time to work on the low speed. You said you've changed the setting from the original. Fortunately, all is not lost. The Saito manual tells you how to get the low speed needle close to the original factory setting. In case you don't have it, here's a link: http://www.horizonhobby.com/ProdInfo...ER_2005_10.pdf . On page 10 is says to set the idle needle to the point where the head is flush with the throttle arm housing.

Once you've reset the needle to the original setting, here's a little trick I learned to get the needle close to right. With the power still attached, run the engine up to full throttle to clear out the carb. Then bring it back down to idle for a few seconds. Once the idle has stabilized, remove the power. If the engine slows considerably, the low speed needle is too rich. If it doesn't slow at all, it may be too lean. I suspect the reason this little test works is because when the engine is too rich, the extra fuel hits the glow plug element. While the power is on, the battery helps keep the element glowing, but once it's removed, the wire is cooled and the engine slows. Once you've got it close, you can fine tune to ensure that you've got good transition.