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Author Topic: Dngine running poorly! Fuel tank problem????  (Read 552 times)

Offline frank mccune

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Dngine running poorly! Fuel tank problem????
« on: July 01, 2013, 07:50:21 AM »
     Hi;

      My friend was attempting to fly his Flite Streak with a ST G20/23 and a Brodak 3 oz. uniflow tank.  It was a terrible run all day

      The symptoms are this: The engine is set for a rich 2 cycle at launch.  When airborne, it goes into a very lean and fast 2 cycle.  After about 90 seconds. it breaks into a very rich 4 cycle untils the tank is near empty and then back to a  screaming lean run until it is out of gas.
 He caps off the fill vent before launch.

      What is the problem?  I would like to take the tank apart and check the plumbing as think that it is incorrect! Since I am not permitted to rework his tank, I can only guess what is the problem.  Any thoughts?

       I have made quite  few Uniflow tanks and they all worked perfectly.

                                                                      Stay well,

                                                                       Frank
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Offline Steve Helmick

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Re: Dngine running poorly! Fuel tank problem????
« Reply #1 on: July 01, 2013, 10:33:44 AM »
Quite possible an internal problem such as a split brass tube. One thing you might be permitted to inspect is the overflow cap. Too many put a short screw into a piece of tubing. That may work, or it may not. A BB shoved into a piece of tubing is a sure seal (no ice cream jokes, please!).   :o Steve
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Offline Jim Thomerson

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Re: Dngine running poorly! Fuel tank problem????
« Reply #2 on: July 01, 2013, 11:03:02 AM »
Does sound like a tank problem.  I have the same set up and suggest running a venturi with a 1/8 in hole in it, and a 9 x 4 prop. A 10 x 4 might work.
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Offline Dennis Toth

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Re: Dngine running poorly! Fuel tank problem????
« Reply #3 on: July 01, 2013, 01:42:55 PM »
Frank,
I have gone through this recently, you didn't mention if he is using muffler pressure. The Symptoms sound like it is on muffler pressure with a high suction venturi. Try running it with an open uniflow setup.

Also add a couple drops of Armor all to the fuel to stop foaming. Make sure the NVA is sealled against the sides of the case where it goes through the venturi and that the lock collar is tight. The ST G20 I believe is an iron piston so the oil content should be at least 25% most of it Castor.

Best,           DennisT
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Offline frank mccune

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Re: Dngine running poorly! Fuel tank problem????
« Reply #4 on: July 01, 2013, 06:08:48 PM »
    Hi Dennis:

    I had a bit of time to reflect on my friend's tank problem and I think that your are correct! 

    His ST .23 has a venturi from a ST G20/15D.  It has a very small hole, about 3/32" and with the muffler pressure, it was getting too much fuel or ...? I looked at both of my G20 ST engines,one Diesel and one glow, and the venturs are different! After the muffler fell off, the engine ran great!!!!! Well done Dennis!

    I too have a Flite Streak that I am going to drill for the ST G20 case and interchange my Diesel with the glow engine.  I doubt that the Diesel will go as fast as the glow as it is a bit smaller. The .15  has 44% of the displacement of the .23. I hope that the .15D provides a nice slow flight.

                                                                                             Well done Dennis,

                                                                                              Frank
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Offline Dennis Toth

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Re: Dngine running poorly! Fuel tank problem????
« Reply #5 on: July 01, 2013, 08:19:20 PM »
Frank,
Glad that worked out, don't count the diesel short. You need to run a little more pitch (5 - 6). I ran a PAW 15 on a full Ringmaster on a 9x6 prop and it was as strong as a 35 with less weight. The ST is a little shorter stroke so it will like a little higher rpm. If you do a search on the ST 15 diesel on here and SSW you will get lots of information on what some of the diesel guys have used on this engine. It is a very strong motor, GMA used an Oliver Tiger 15 in a ship called the Peacemaker (it was later kitted by Top Flite). Search that and get the article he gave lots of information on using the diesel.

Best,            DennisT
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Offline Jim Thomerson

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Re: Dngine running poorly! Fuel tank problem????
« Reply #6 on: July 01, 2013, 09:02:52 PM »
i've flown ST G20-15 diesels a lot in OTS ships.  I run an 8 x 4.  I have run a 9 x 4 and it was OK.  The engine is happier on the 8 x 4 however.  According to the Aeromodeller review, peak HP is at 15,000 RPM.  An 8 x 4 will turn 14,000 on the ground.  A 9 x 4 is around 12,000.  A ST G20-15 diesel should fly a big Flite Streak just fine. Probably want around 55 ft 012 lines, however.
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