Hello all,
at WC I've seen that dual tanks were installed on some planes, in particulare there were one big tank linked with a very small one.

Someone already knows such a solution? Why is that needed?

Very simply put, the large tank feeds the smaller tank and since you are always drawing fuel from the full small tank you eliminate any possibility of air bubbles in your fuel to the carb.

Thank you fancman. Also pump-equipped engines (as OS 140 RX) need this solution? I'm mounting my OS 140 RX on my new pattern, I would be very glad to know this in advance!!!

An OS 140 RX doesn't need anything special. Just run a fuel line straight from the clunk with one filter.....tee it and install a dot for fueling or run it outside and make a break point for same....and just run the vent line straight out the bottom of the plane. Nothing fancy is needed.

Some put a loop in the vent line, some use a check valve, etc. To me this is dead weight and unneccessary in my experience, but if it makes you feel better do it

-Mike

I agree with MHester. I run an OS 160FX with Perry Pump and have found no need to use a header tank even with my fuel tank mounted at the plane's CG.

If you have pump , it will work very well , but if don have , you will have a problem, for example , i have a 91FX with header + tuned pipe,this is in my LEO f3a 110 , and i put a header tank becuose the "main" tank is on the CG and it does not work properly(an other reason is becosuse i fly at 7000¨).i can fly well with the nengine , mounting the "MAIN"tank ahaed.

Sergio

Hi
Yes it's to avoid bubbles.
With Yamada 140 Dingo or 160 Dingo if we use only one tank we have to equip our tank with a spécial
fuel tank foam clunk sold with the engine otherwise engine stop because bubbles.
If we don't want to put this fuel tank clunk we have to put 2 tanks in line.
picture 1 : special foam clunk and picture 2 : installation of 2 tanks

Thank you guys, you really explained me how the stuff works!

Hello , someone know how to reduce or eliminate the leaks of fuels by the vent line as ventury effect when is using a pumped engine, off cors, the vent line is not plugged to the muffler or pipe.

Thank you

Jorge lozano

Hi
with no pressuriezd tank I use a check valve.
little piece under reso.

Very interesting. I've been having a devil of a time with my YS63S. Broken in on 20/20, runs great when first started cold but after 5 - 6 minutes, begins to run eratically, always followed by dead stick landing when throttled down to idle. Tried to adjust with mid-range regulator and idle bleed air needle screw adjustments. Not having much luck. Never gave bubbles in fuel tank any thought. Tettra tank mounted over CG with brass clunk. One fuel and one pressure line with aluminum fuel dots tee'd in. Not enough room for a smaller header tank, so, does YS sell the "special foamie clunk" separately ? Don't want to ship back to YS without trying to solve on my own.

Steve H

Shomenda,

The foam tank clunk will not solve you problem I promise. The YS pressure system on the standard type of YS engines keeps the foaming in the tank to a minimum. You settings are off...or another option is cooling. Perhaps you are not getting enough cooling to the 63. What RPMS are you running on it...the 63 needs to be turning about 10,500-11,000 on the ground at full power. If you are getting less then perhaps you have too big of load on the motor and its getting hot. There can be lots of things that cause the motors settings to be off but the reality is the foamy clunk really doesn’t change mixture setting and problems. It keeps the air bubbles from getting in. If you were getting air bubbles on the pressurized YS 63 then something is wrong with the tank (pin hole in fuel line, cut line leaking fitting or fueler valve) something else. The DZ motors (Direct Injection) motors are the ones that benefit from the foam clunk as the tank doesn’t have the pressure system to keep fuel flow steady from the tank side of things.


As for the Header tanks...They are absolutely not needed on a pumped engine. That being said I run the YS 140 and 160DZ in my models and I choose to use the header tanks. Here is why:

The idle is improved by a ton. The motor never gets a burp as it’s running out of fuel. And it’s very easy to start this way. Since the smaller tank (I use a 2oz) is always full during my flight to the engine it acts like it has a full tank of fuel all the time.

The next advantage is I have the header tank up near the firewall and this gives me some ballast that is removed when putting the model on the scales. Since the header tank really never gets drained it moves my CG more forward and the model flies better with this CG. The result is carry 2-3oz of weight forward to get your CG and be able to remove it when checking weight on the models. The result is using the ballast for something. I now balance my model with the header tank full and the main tank on the CG dry. Result is the CG doesn't change when the main tank is being drained and yet the C G is in the right spot for me. For years I have been moving my tanks forward of the Cg to get the same effects from the main tank. I want to use the Fuel to help me balance the model. My Smaragd had the rear of the tank touching the front edge of the wing tube. The result was the Cg would shift about 6mm from full tank to empty tank. Since I was only using about 1/2-2/3 a tank for a full sequence the result was a Cg shift that I could not really feel during the sequence. The header tank helps this situation of Cg shift and still gives me the forward CG that I want. The tank mounted on a Dave Brown pipe mount weighs just one ounce...and it full of fuel is a little over 3ounces of weight, for tank mount and all.


This I started this on my models this year and saw improvement in the way the motor responds. We have also tried it on a Webra 160 (MC carb) and an OS 140 RX. The results were better consistency and idle. In fact this made the motors run easier as the small tank was up closer to the pump and it was delivering fuel easier to the motor. The result as mixture setting changed a little and the motors really came to life and ran more consistently. This was my problem always with the 2 stroke was consistency. Throttle up to 1/2 from idle and check rpm...the throttle back to the exact same stick position from full power with it up on the pipe. The result was the motor would always be running at higher rpms coming off the full power setting than coming up from the idle position. I also found it really tough to get the motors rich enough on idle to get them to instantly drop into an idle. The 2 strokes always spool down and the leaner the low end is to get the transition right the longer it takes to spool down. The header tank helps this as it enables the pump to make changes faster to fuel delivery. The reason is the fuel is being pulled from a closer reservoir of fuel and the line losses through that small little fuel line is less.

The side benefits of never running out of fuel or getting even a single burp on the motor is that the motor never gets a lean run. This saves parts, and rebuilds. Of course you get no warning when its out of fuel it just runs dry and quits so you have to pay attention to your timer.

By the way I can fly about 14 mins on the 160DZ flying the Prelim sequence stuff and not have the motor burp once. Upon landing the header tank is still full. Just my thoughts on the subject and why I choose to use it. I think it can help lots of setups. But it is not a solution for a bad running motor it just improves an already working system. I use the foam clunks in both tanks.

HI all
i have a problem with mi engine(91FX)in my pattern plane doing the P05 (2 revesed spins), buecouse my engine turn off , when i do this manuever the engine turn off. what is that?how can i fixed it?.
If i put a check valve in the press line?
thanks,
Sergio.

Troy,
thank you very much for your extensive answer! It will certainly be useful to many, myself included!!!

Hi Troy,

I had similar experiences to yours by using a header tank.

My setup is slightly different to yours. I decided to run a fixed pickup line in the header tank. The pickup line (brass tube) is located in the exact middle of the fuel tank. This makes it impossible for the engine to suck air unless the header tank is less than half full. The main tank uses a conventional pickup. (No foam clunks used -only to reduce maintenance further).

Otherwise I am wrapped in the results.

Peter

Thanks for your help, Troy. Good to hear from you. This YS63S (regulator up front) has over two gals. run through it. 12 X 7 APC, tachs @ 12,000 rpm, full power on the ground. After reading your thread, it appears the problem I'm experiencing may be heat related. After all, it's been a long HOT summer in Central Florida. The engine is hard mounted inverted and is surrounded by a narrow fiberglass cowling with large hole in front for the cylinder assembly and regulator to protrude through. There's another hole (half-dollar sized) in the bottom for access to the glow plug, etc. and small hole in the side for the high end needle and idle mixture screw. I've always been told the head of the regulator screw should be flush (or close to it) with the body sidewall. At present, it's turned clockwise (three turns from flush) to lean. The idle mixture screw has been turned clockwise to enrichen to compensate.

One last question, when advancing the throttle from idle to full power after allowing the tank to pressurize, the engine bogs down. Is this an indication of a lean condition or a rich condition. The YS manual that comes with all non-fuel injected engines provides instructions on adjusting the regulator to compensate for lean/rich conditions but it seems to take a trained ear (not mine) to conclude whether the transition is lean or rich.

Steve Homenda