I have received my new Irvine .53 from Just Engines (and it is a work of art!). Am breaking it in now by 2-3 minute full throttle runs at 1 3/4 needle setting as recommended. I have run a couple of 12 oz tanks through it with these cycles and I haven't noticed a smooth transition from low to high speed. It hesitates, then catches up, then slowly speeds up to full revs. I have leaned it out a little and it still does the same thing. Is this just a sign that it isn't broken in yet? Everyone else that has one of these engines seems to have been able to fly straight out of the box. Suggestions?

It just sounds like it may be set too rich, to me; if not the HS needle, then maybe the LS. Try leaning it in to a nice flying setting and see if it improves; it's ready to go now, anyway. I never noticed any difference in the way mine ran from right out of the box till after two years flying; it's run great from day one. And the low speed needle on mine has never been reset from the original factory adjustment.

I had an OS 61FX that behaved similarly...try attaching your glow clip and check transition. If it behaves significantly better with the glow attached, you are either way too rich or probably need a hotter plug. Mine turned out to be the latter...I used a Fox Miracle 4-cycle plug and it behaved much better.

Remember a couple of things when you are tuning and engine, the idle mixture screw determines the low to mid-range, the high end needle valve controls the mid to high end mixture. If the engine lugs going from low to high, the idle mixture isn't correct.

Always remember to check both settings before making a final call.
If I adjust the low end, I run it up to full speed, set the high end at this time, and then idle it back down to see if the change worked. Adjusting one side WILL affect the other. You should let it idle for 30-45 seconds, at a very low setting, and then go to full throttle and see what happens. If it blows raw fuel and smoke and still hesitates, the low end is still too rich. If it just dies, it is probaly too lean.

Another way to see if you have a good fuel-plug-mixture setup is to see what happens when you take the glow starter off. If the engine drops RPM, it needs something.

Irvine engines are good engines, but they are not made to perform like a high performance engine either. They tend to be real "course" in any changes and will tend to go to the lean side in flight if you are too close to the "edge". You should be able to get a good idle and a good transition with it though, mine ran like a top for a good long time before I gave it to a friend, but it never would transition like a race engine.

Hope this helps,