goes rich...

[Bootlegger]

   Hey guy's,  I posted this in the engines section also, I am running an OS 32 SX with some re work ( hemi head, blocked boost port) and as the flight progresses it goes richer !!
  Uniflow tank open to the atmosphere 5% nitro 22% oil half and half Thunderbolt idle bar long reach plug. It starts off real well, then as the run progresses it starts going rich.  It re starts well even when hot, and then it goes rich again..
  I am open to suggestions as waht to look for..

[GEOFFREY]

I believe someone at our site had same problem. he changed length of  uniflow air tube . he added  and it did work ?? Leo  i believe   

[Bootlegger]

      Jeff, Sure do thank you for the suggestion. I'll try that at the next flyin session.
    If any one else has some suggestions PLEASE let me know...

[phil c]

You can also try putting a restrictor in the uniflow vent.  Brass tubing, nested down as far as 1/32 i.d.  Uniflow tanks do tend to go a bit rich at the end.  You can also try extending the vent with fuel line and tuck it in somewhere behind the engine so it isn't exposed directly to the airstream.

[Bootlegger]

   H^^Got  the model back in the air this morning and made about 6-8 full flights and the engine ran without going rich at the 8's . The only difference is that the weather was cooler today by about 20-25 degrees.
Thought I'd post what I'd found out in case someone has this problem. Today and earlier I'd been running Powermaster 5% fuel 22% oil blended....
 

[tom hampshire]

Your problem might be that the fuel is being heated by proximity of the tank to a muffler or pipe header.  This will thin the oil as the flight progresses, increasing the fuel draw and richening the setting.  Wrap an exposed tank in foam rubber, or add a heat baffle made of aluminum foil wrapped around a piece of thin styrofoam.  I run these between pipe headers and the tank to avoid this problem.  Tom Hampshire

[Bootlegger]

Tom, Thanks for the hint. This set up is an OS 32 SX side exhaust, since the weather has changed (cooler) it isn't running rich at the middle of the pattern.
  I am planning on going to Dallas this weekend and sure hope that it performs ok..