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Author Topic: K&B 61 tank question  (Read 547 times)

Online Dane Martin

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K&B 61 tank question
« on: November 13, 2017, 08:40:04 AM »
I've tried the search function and get nothing, so I apologize in advance for repeat questions. My RM1000 is my favorite plane to practice the pattern with. It has a K&B 61, .280 venturi and a 13x6 prop. Every flight, right after the triangles, it leans out beyond what's flyable. It does it on the ground also, after that amount of run time. I'm like 99% sure it's the tank. Sooooo, what tank should I buy as a replacement? I was thinking the chicken hopper 5.75 from RSM.


Offline dennis lipsett

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Re: K&B 61 tank question
« Reply #1 on: November 13, 2017, 10:04:14 AM »
Dane,

Sound like your tank has an improperly located pick up line. I abandoned hard tanks for profiles a long time ago. I use an RC clunk tank set up as a uniflow with fuel tubing and pick up weights. Mine has given me consistent runs on my Pat King Ringmaster 853. Modern versions of the Ringmaster with decent airfoils are light years ahead of the original and it is no small wonder that they have gained so much popularity recently. Oh, and my run is consistent and only speeds up for 3 laps then burps and shuts off. The tank is completely dry

Online Dane Martin

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Re: K&B 61 tank question
« Reply #2 on: November 13, 2017, 10:32:55 AM »
Thanks Dennis. This is my 800 tank. Obviously a 4 stroke in this pic, but would the tank mounting be similar? The 4 stroke has suction no matter what, it seems. Would this tank mounting position be too tall on a profile with a 2 stroke?

Offline Motorman

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Re: K&B 61 tank question
« Reply #3 on: November 13, 2017, 07:40:50 PM »
Try moving your vent tube farther forward in side the tank.


MM
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Online Dane Martin

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Re: K&B 61 tank question
« Reply #4 on: November 13, 2017, 08:04:29 PM »
Let me put up pics of my actual tank. Now that I've taken it apart, I'm probably more lost. It is clean, the pick up line is intact and there's no leaks anywhere. Before I pulled it apart, I pressure and vacuum tested it. I don't get what's going on unless it's in the engine..... the plane has run fine on this set up for years, now all of a sudden is goofy?

Online Dane Martin

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Re: K&B 61 tank question
« Reply #5 on: November 13, 2017, 08:06:24 PM »
Inside tank pics
Could the pick up line be too high? It's above the center when mounted.

Online Dan McEntee

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Re: K&B 61 tank question
« Reply #6 on: November 13, 2017, 08:20:25 PM »
  If it has run the same with this hardware for some time as you say, then yes, something has changed. You can mount the tank the same as for your four stroke, and a quick test would be to try your four stroke tank, even though it may not be big enough. If it make the run better, just copy the plumbing on a tank of larger capacity that the K&B would need. Your current tank is not a unilow. For the K&B I would suggest a uniflow set up. The four stroke is a different animal, and I don't use a uniflow on my Saito powered Score because it works better. If you don't currently run pressure, try that also. Have you checked the engine back cover screws? Venturi and spray bar sealed well?
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Online Dane Martin

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Re: K&B 61 tank question
« Reply #7 on: November 13, 2017, 08:55:42 PM »
Hey Dan. I had it on pressure first. Well that's how it was given to me anyway. The problem started on pressure. I replaced all these lines thinking a hose was leaking. It ran identically. I removed the lines and ran it straight suction. Identical run. I'll try the 4oz tank. Basically because I have nothing else to test with. I have two spare rebuilt K&B 61's if I need to move forward with troubleshooting after that.
Thanks Dan. I'll pull the engine real quick and check the back plate. The venturi seal was cool.

Online Dane Martin

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Re: K&B 61 tank question
« Reply #8 on: November 13, 2017, 08:58:54 PM »
In fact, it was the day of the ringmaster fly-a-thon.  We were flying it, Joey, Dan Mosley and myself. Towards the end of the day, second to the last flight it leaned out. After I landed it, Joey checked the tune, launched it, it felt good for half a flight and leaned out. He told me is my plane and my problem now. Lol

Online Dane Martin

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Re: K&B 61 tank question
« Reply #9 on: November 14, 2017, 09:06:34 PM »
I pulled the engine from the plane and checked the back plate, and the venturi seal. The only questionable thing I found was a wierd fibrous material in the NVA. I'm hoping that's my issue, because I can not find anything else to be a problem. So I soldered my tank back together, pressure tested it, fixed a leak and pressure tested again. I guess I'll test again this way real quick to verify any "fix" I may have made inadvertently.

Online Dane Martin

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Re: K&B 61 tank question
« Reply #10 on: November 27, 2017, 06:15:50 PM »
I tested again with my inspected tank. It did the same. I changed to a fresh engine. Same series K&B 61, nva and venturi. It did the same thing. It's gotta be the tank somehow. So I changed to the clunk tank. I took everyone's advice to heart,  it just took a while to find a 6 oz tank and order it and wait for delivery. I will hopefully test tomorrow. Today was too windy. It felt like it was gonna blow our shop doors down!

Online Dane Martin

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Re: K&B 61 tank question
« Reply #11 on: November 27, 2017, 06:21:42 PM »
  Your current tank is not a uniflow For the K&B I would suggest a uniflow set up.
  Type at you later,
    Dan McEntee

Dan, on this clunk tank I made it uniflow. Also, I made it so the vent and pick up line height is adjustable by turning the stopper. Joe Gilbert and Don Cranfill showed me that in 2013. It took me this long to understand why they did it. Lol

Online Dane Martin

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Re: K&B 61 tank question
« Reply #12 on: November 28, 2017, 10:29:42 PM »
I think I was able to stuff 5.5 oz in this 6oz tank. I flew the full pattern first flight, and it made it ok. No room for any messing around after the clovers though. I did two or three laps, started another clover and it shut off! Completely dry. At least the fuel delivery seems to be working properly now. I gotta put a bunch of flights on it to see if I need more tank. Or maybe a 13x5 prop and lean it out just a touch? Anyway, let me put up more flights before I make any more changes.
Thanks guys.

Offline Steve Helmick

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Re: K&B 61 tank question
« Reply #13 on: December 31, 2017, 11:57:10 AM »
Some have reported similar malfunctions being due to cracked/punctured/corroded brass uniflow tube inside the tank. What is happening is that the uniflow works as advertised, until the leak in the uniflow tube is uncovered as fuel burns off, then it reverts to being a standard tank. Hasn't happened to me, tho.  H^^ Steve
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