So it would seem the ASP .25 is a popular choice for speed limit combat.  I would like to know anyones thoughts, experiences trying to get these to run properly.   I have mine set up with the typical os .10 remote needle, and an 8-5 and 9-4 APC prop.  10% Powermaster fuel, with castor added kicking it up to 20% oil.

 The problem I am having is going lean in the loops.  They do require to be sent off rich. Richer than I am used to with the Foxes or Nelsons that I used to run.  I am not sure if there is an issue with the venturi or not, it is really short, and does not give the air much time to smooth out.  I was also running them with all of the head shims in from stock. I am wondering if they need to be removed to raise compression? 

  I have run a lot of engines on pressure like this, and never had one so finicky.  This is not a good recipe for combat, so I have gone another direction as I have several other engine options for speed limit.  Finding this as a challenge though, I would like to solve this problem though, as I know there will be others trying this setup and may need some answers.

Check which OS NVA you have.  They made several for different RC carbs but only 1(for the OS10 RC) has .35mm threads.  The others have .5mm pitch threads and are too coarse for a heavy bladder.  A couple of them also have a much coarser clicker that makes it worse.

You can try 15-20% nitro.  That gives you a broader adjustment range but the motor will use more fuel.

I had pretty much resolved that the engines will not work for me, and this is why.    I used the same needle (which I have been using for close to 20 years on my foxes and Nelsons), bladder, prop and plane, but I swapped in an OS .25 FP.  It worked perfectly.  My conclusion is there is an issue with the venturi configuration, the liner timing or quite possibly that I fly at 5'200 altitude.   I have read where people have had problems getting the OS .25 FX to run properly for speed limit combat, and this engine is somewhat of a copy.   I was just trying to see if anyone had a recipe for success on this engine. 

    Seems to me someone had set up a bunch of these and posted on the MACA FB Page. They listed the venturi size and were using a Traxxas R/C Car NVA. If you are on FB and a MACA member you should ask your question there. Mike

Fredvon,   

Yes, I read the article a while back, and I have actually converted an FX for combat.  I was never able to get it to run properly come to think of it either.  If you look at the bottom of the article, Buzz talks about going lean problems, and mods he made to remedy it.   I have corresponded with Buzz about this and he said he does not use the engines anymore.  It is just too finicky a set up for some reason.  I have been told to use all synthetic oil, or as Buzz said to kick the nitro content up.  These seem like band aid solutions, as higher nitro would cause other issues, like higher speed which you would have to dial out.  For me,  special fuels are kind of out of the question, as good glow fuel around here is hard to get, and shipping it is expensive.

 I am going to run the OS .25 FP this season, as I am not having any issues with them.  But my question now is what would it be with the design of these engines would cause them to go lean 9in the loops in particular)?  WOuld it be the configuration of the ports in the liner, the timing of the crank?    I think this is the only engine I have had that did not respond well to the application of a bladder fuel system.