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Engine basics => Engine set up tips => Topic started by: Paul Taylor on February 22, 2011, 08:19:57 PM

Title: OS Burp?
Post by: Paul Taylor on February 22, 2011, 08:19:57 PM

So I was flying my SkyRay today with a OS .25 on a uniflow tank. Engine ran fine up right and inverted. But when doing outsides the engine seemed to go rich only on the second outside. It also did it the same thing in the outsides on the over head eights.

It was almost like a soft burp.

Thoughts?

Title: Re: OS Burp?
Post by: Brett Buck on February 22, 2011, 08:33:48 PM

Quote from: Paul Taylor on February 22, 2011, 08:19:57 PM

So I was flying my SkyRay today with a OS .25 on a uniflow tank. Engine ran fine up right and inverted. But when doing outsides the engine seemed to go rich only on the second outside. It also did it the same thing in the outsides on the over head eights.

It was almost like a soft burp.

  Switch to suction, and richen the needle to compensate for the change from beginning to end.

    Brett

Title: Re: OS Burp?
Post by: Paul Taylor on February 22, 2011, 08:39:01 PM

Thanks Brett,
Can I use the same tank and just change the plumbing?
Or do I go to a clunk tank?

Title: Re: OS Burp?
Post by: Brett Buck on February 22, 2011, 08:42:25 PM

Quote from: Paul Taylor on February 22, 2011, 08:39:01 PM

Thanks Brett,
Can I use the same tank and just change the plumbing?
Or do I go to a clunk tank?

     Plug the uniflow vent (after fueling) and leave the overflow open.

    I presume that this is a 25FP or LA, and that you are running an APC 9-4?

    Brett

Title: Re: OS Burp?
Post by: Dan McEntee on February 23, 2011, 12:37:28 AM

   Raise the tank 1/8". Pay closer attention to your upright and inverted lap times. You could be a couple of hundred RPM slower (richer) inverted and not be hearing it.  Should be the same for pressure or suction.
  Type at you later,
   Dan McEntee

Title: Re: OS Burp?
Post by: Paul Taylor on February 23, 2011, 06:26:00 AM

Quote from: Brett Buck on February 22, 2011, 08:42:25 PM

     Plug the uniflow vent (after fueling) and leave the overflow open.

    I presume that this is a 25FP or LA, and that you are running an APC 9-4?

    Brett

Got it ! Thanks Brett,
The engine is not the FP or LA, it's the FSR... something like that. And yes 9x4 APC.

Title: Re: OS Burp?
Post by: Scott B. Riese on February 25, 2011, 03:47:07 PM

What glow plug are you using? Has to be a HOT one. What Muffler are you using. Venturi Size? NVA Type? Do you have about Three drops of Armorial in your fuel? Check the back plate. One Head Gasket .005 to .008.

If it's an FSR 10x4 prop is what you need...same as the LA-25

Most likely it's the Dang Profile set up.


Uniflow ....3/16 above the center of the engine. If it keeps it up...the burp... Try pressuring the tank.

Title: Re: OS Burp?
Post by: Chucky on February 25, 2011, 06:18:34 PM

Without knowing more about your setup it's hard to say what the problem might be.  This engine has no inherent burp that I've ever observed and I've got a lot of time with them.  Here's my setup:  stock 25 LA-S venturi with FP-20/25 NVA, metal backplate (FP-20/25 or Curtis Shipp) installed with no gasket and high temp silicon, OS A3 glow plug (hot) or similar.  If the model can tolerate it, box stock tube muffler, if not, then Randy Smith tongue muffler or other lightweight alternative -- muffler hasn't been a big deal for me except for establishing CG.  Home brew 2.25 oz metal wedge uniflow tank (1" high, 2.25 " long) on muffler pressure.  Wildcat Premium Extra 15% nitro fuel (18% total oil).  APC 9x4 plastic scalpel.  Never discount the possibility of a messed up tank.  These have probably cause more engine run problems than anything else.