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General control line discussion => Open Forum => Topic started by: Bootlegger on March 04, 2009, 11:32:48 AM

Title: ...Awrite, why???
Post by: Bootlegger on March 04, 2009, 11:32:48 AM

OS 32 SX 5% fuel, 6oz round clunk tank, and the thing "surges" in flight.  Up and down, fast then slow, will not hold a steady needle, the tank is uniflow open to the atmosphere, glow plug is Thunderbolt idle bar long reach, so it should be a "hot" plug.
  Any suggestions ???    Got me goin' bonkers...... n~

Title: Re: ...Awrite, why???
Post by: Garf on March 04, 2009, 11:43:35 AM

Could be caused by tank walls flexing. Try muffler pressure or un-uniflowing it.

Title: Re: ...Awrite, why???
Post by: Mike Anderson on March 04, 2009, 11:53:15 AM

Quote from: Bootlegger on March 04, 2009, 11:32:48 AM

OS 32 SX 5% fuel, 6oz round clunk tank, and the thing "surges" in flight.  Up and down, fast then slow, will not hold a steady needle, the tank is uniflow open to the atmosphere, glow plug is Thunderbolt idle bar long reach, so it should be a "hot" plug.
  Any suggestions ???    Got me goin' bonkers...... n~

Could be a compression leak - backplate, head, or glow plug.  We've had a LOT of loose center posts in brand new glow plugs, lately, or that go leaky in the first run.  Not Thunderbolts, but more than one brand of others.

Good luck.

Title: Re: ...Awrite, why???
Post by: James C. Johnson on March 04, 2009, 11:55:33 AM

Be sure there are no pin hole leaks .. I had this problem once and it drove me nuts.. pin hole in the tubing was the cause..

Also old fuel might do this..

Jim

Title: Re: ...Awrite, why???
Post by: Neville Legg on March 04, 2009, 11:57:16 AM

I was typing exactly the same, when my computer said there was a new post,


Cheers   Neville

Title: Re: ...Awrite, why???
Post by: Mark Scarborough on March 04, 2009, 12:36:31 PM

what kind of plane profile? it could easily be fuel foaming as well if the tank isnt mounted well. resonant frequencies causing foaming and such,, just another thought

Title: Re: ...Awrite, why???
Post by: Bootlegger on March 04, 2009, 12:43:18 PM

  Yes, it is on a profile, and could be "resonance" however same set up on another profile, same engine, tank, glowplug, and fuel, just pulled engine, head, back plate tight will change glowplug and try that. Gotta keep looking and when I find the trouble I'll report back what it is...   Thanks for the suggestions... :!

Title: Re: ...Awrite, why???
Post by: John Stiles on March 04, 2009, 05:21:00 PM

Cracked fuel line..I've had the same thing happen to me...always just replace the line! ;)

Title: Re: ...Awrite, why???
Post by: john e. holliday on March 05, 2009, 06:23:24 PM

With me of all things, it was a fuel filter.  One of the small ones.  Had maybe a couple dozen flights on the plane when the engine started acting up.  Replaced plug, fuel line and even tried different fuel.  Finally Bender said lets pressure test and the filter started spewing fuel.  A couple of wrenches to tighten it and every thing went back to normal.  DOC Holliday

Title: Re: ...Awrite, why???
Post by: Garf on March 05, 2009, 09:45:33 PM

It's amazing what pressurising the entire fuel system will show up. Whenever I have an unexplainable problem, that's what I do.

Title: Re: ...Awrite, why???
Post by: Bootlegger on March 06, 2009, 04:18:25 PM

 H^^  Thanks for all the suggestions guy's, weather still preventing any flying will report back when I get it in the air.  Again thanks

Title: Re: ...Awrite, why???
Post by: Bootlegger on March 08, 2009, 05:43:37 PM

  Got airborn today, put 3.5 oz in the tank as I had been "short tanking" it with 2 oz, today got in two flight's and it ran like a clock.
   Hope this helps someone else.......

Title: Re: ...Awrite, why???
Post by: Jim Kraft on March 08, 2009, 06:30:47 PM

Was it the plug?

Title: Re: ...Awrite, why???
Post by: Bootlegger on March 08, 2009, 07:34:02 PM

 Yeah Jim, I did change the plug and I pressure checked the tank (no leaks) then checked the filter, all fuel lines and they didn't leak either, no leaks in the fuel system anywhere.
  The engine OS 32 SX now runs like a top.