I had previously noted that the "new" 25LA was much stronger than the originals, and a bit stronger than the 20FP. Now, I have gotten a fair number of flights on it, and it has settled down to *outstanding* performance and consistency. The setup is
*STOCK* 25LA-S (new version)
*STOCK* E2030 muffler
*STOCK* Venturi and rear needle assembly DO NOT change it to front needle, or at least don't expect it to work better.
*STOCK* OS A3 glow plug
APC 9-4 bone stock, with TE sanded down so it won't cut your finger
10% RO-Jett fuel - 3 oz for a full pattern
Launch setting - Find click of needle closest to 13100 RPM, if there isn't one, use the richer/slower notch. Engine should be mostly 2-stroking but occasionally blipping into a 4/misfiring
Tank - Sullivan SS-4 set up for suction, with muffler pressure into suction/overflow vent.
It is a better stunt engine than the 20FP, the run quality is at least as good, and it is more responsive in the maneuvers. Takeoffs are like an electric, the engine seems to hardly unload at all (which explains the reason it blasts off the ground, and its because it has much more "power"). This worked at anywhere from sea level and 70 degrees and moderately humid, and 100+ degrees and not at all humid, on the Skyray/Flite Streak sized models.
I cannot guarantee that this is the best possible setup, and using a 10-4 seems like a realistic possibility, but it works awfully well, better than most people have ever had in their lives in terms of stunt run quality. Jim and I cranked out 5-6 flights yesterday, all with perfect runs, from the early morning with overcast and rain to 100 degree California Sunshine. This is consistent between several different engines we have around here, all were much better than the old ones.
You must have the *new* 25LA. I finally got a hold of a couple of the ~10-year-old blue 25LAs for a comparison test. They were both the same, and much weaker than the "new* version and weaker than the 20FP. A good test is to set it up on the stand, put in 10% and bolt on a 9-4 APC. Start with the pre-set needle, start it, and run through a 16 oz tank of fuel. The engine will rapidly go richer and richer, keep turning it leaner to keep the same RPM, which will be around 12500. Let it cool (DO NOT touch the front end or venturi for a while after this run because you will be sorry...), then start again, and peak it out. The "new" version will easily hit 14200-14300 on 10%. The old version, by comparison, will be good for around 12900. A 20FP will be around 13300-13400 peaked out.
I don't have a 25FP to compare to, but I think the performance is about on a par FP, but the LA runs better.
The only thing wrong with the rear needle is that it come in a bad position to get broken off on a profile, and that's exactly what happened. I haven't tried it but I think you should be able to turn the backplate 90 degrees clockwise (as viewed from behind) but there is a flat on one side of the backplate that seems to be for liner clearance. That puts the needle up behind the cylinder head on the muffler side, which is harder to access and might cause you to burn your finger, but will not get broken off.
The needle it a bit touchier than the front needle but it works just fine.
I don't know how to distinguish between the "new" and poor-running "old" version from the outside or from looking at the box. There seems to have been some inadvertent or seemingly irrelevant change made (maybe in the processes or materials) that made *all the difference in the world* to the performance.
Brett