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.