Nice set up. What pitch prop are you using?                                                                                     

A lot of things happen that day , Jim tryed diffrent props ended up with a 3 bld Bolly 12x5.5 will probably cut it down to 11 1/2x 5 and the fuel went from 10% to 22% and also doubled the head shims from stock to get a 4 cycle, this still not in stone , but is a test. the Stalker is 2.2 not sure what that means . Ted or Jim can clear this up.

As ARF Score goes Mike Has a Super Tiger in it and has some great flights , at 5.0 -5.7 0n 70 ft lines, Mike knows the Score trim & Balance vary well. 

I was sort of hoping Uncle Jimby would post something on our work last Sunday.  He must be out refinancing somebody's house or something.

Jim did ask me to come out and help him scratch his head over some less than sparkling performance he was getting from his .61.  He had it set up similar to one used succesfully down under but there was something missing.  He was using an Eather 12X4.25 three blade prop, running 22% nitro mostly synthetic fuel and using the largest of three venturis supplied with the engine (.300 or so with the two others around .290 and .280 respectively).  It was running the stock head shim which turned out to be 0.015" thick.  A uniflow plumbed plastic tank was behind the engine with provisions for running suction by capping the uniflow and leaving the overflow vent open.  The plug was a Thunderbolt four cycle.

The engine would be set rich on the ground in the low to mid 7K range and the problem was as stated above.  After launch it would go to a strong lean (but not meltdown range) two stroke with laps in the low four second range.

We diagnosed the problems as follows.

The venturi was clearly too large which was the main contributor to the runaways.  We did the "one big" step trick and replaced it with the smallest of the three venturis. 

The engine was losing some revs when the battery was disconnected.  We put in a fresh plug of the same time.

The engine gave indications of detonation which was sort of predicatable with the high nitro and stock head clearance.  We addressed this by putting in a bunch more head shim, essentially doubling it to 0.295" and by cutting back to 10% on the nitro.

The engine was running noticably richer inverted.  In need of a tank shim or uniflow tube adjustment.

Flights with those changes followed.  The runway problem more or less disappeared (one strange glich in some round insides sounded like it was going to runaway again but it backed back down inverted and didn't do that again.  The run was not consistent however, and power was not overwhelming although Jimby was doing all the tricks with lap times in the high fives.

We bumped the nitro up to 15% and switched to suction.  We also repropped with another EAther 12.5 but with 5.5 inches of pitch in the heart of the blade and washed out at the tips.

The flights that followed provided very acceptable engine runs in terms of consistency and quality of run.  Power was still nothing to write home about.

I think Jim next steps will be to gradually reduce the head shims and probably trim the prop to get revs up a bit while maintaining the engine is basically a full time four stroke.  The engine never "sounded" happy while it a two stroke.

This is where the engine was when we left the field sunday.  A fairly successful day with some light at the end of the tunnel.

Ted

I do believe that "Champione" Lampione has a Stalker in his Score.  Hopefully he will give us his findings.  He sounded very pleased with the set up.  But I know he has been out with Windy and "da boys" and the Strega ARF...............