Kafin,
It looks like you are connecting things correctly. When you connect the remaining tube to the needle valve, you might consider using a fuel filter in this line. This reduces the potential of getting small particles into the needle valve where it can partially block the fuel flow in the middle of flight and cause erratic and lean running.
A “standard vent” tank and a “uniflow vented” tank will behave a bit differently. Generally, the uniflow seems to run better on more setups, running more steadily, as you noted, with less tendency to speed up. This depends on a lot of different factors. What you show in your picture should work well and is quite common.
You don’t have to run muffler pressure with a uniflow tank. As Porsche Jim suggested, you might not get a steady run if the uniflow vent tube is not in “clean air.” His suggestion about locations is important. On the other hand, I have not seen any noticeable change whether you plug the pressure nipple on the muffler or leave it open. I have seen it discolor nearby (within ¼”) paint, so you know that hot exhaust is coming out of it. On your plane, and the location it is at, it won’t hurt anything.
What Porsche Jim said about the flexible line in a uniflow tank may be confusing. I don’t think there are any current commercially made metal tanks with flexible lines inside them. On your tank, if you shake it and hear rattling—it is broken! Jim almost certainly was thinking of plastic tanks with a clunk. These may or may not be set up as uniflow. Since you have a metal tank, all of that discussion is irrelevant. But, you can make plastic tanks that work very well.
Bill’s comment about moving the end of the uniflow tube inside the tank up and down to adjust the run might benefit from some additional words. If you fly right-side up only, you won’t notice an issue. But if you then try to fly the plane upside down, it might run either faster or slower. To make them even, which is desirable for flying stunts, you can move the tank down if it is faster when flying upside down. And vice versa. Normally, you would start off with the centerline of the tank aligned with the centerline of the engine. Hard to tell exactly from your picture, but you are probably close. Because the engine is sensitive to tank position, you don't want the tank to move around at all or it can affect the needle valve setting and speed. Loose tanks are bad!
Everyone has a preferred way to attach a tank, and they all work to some degree. If you knew you had your tank at exactly the right height (or if you do not plan to fly inverted) you could drill holes in the fuselage immediately above and below your tank and still use the two cable ties. That would prevent the tank from shifting around. Be sure to seal up the holes from fuel though to avoid oil soaking the wood inside. If you put those holes maybe 1/8” above the tank and 1/8” below the tank that would leave room for some balsa shims. That way you can still adjust the tank up and down a bit, while using cable ties. Lots of ways to do this.
Again, back to the upright vs inverted flight tuning: if you were to leave the outside of the tank in the same location, you would have to open the tank up, which can be done, if you are confident you can resolder it without leaks. Then you could unsolder the end of the uniflow tube and move it up or down. However, with a plastic clunk tank, you can merely rotate the uniflow tube causing the end inside the tank to move up or down. This is the “tuning” that Bill was pointing out. For a metal stunt tank on a profile plane, everyone just shims the whole tank up or down a bit to get the run even. Rarely does it take more than an 1/8 of an inch, and for the OS LA, maybe not even that much.
Be aware that having an air leak anywhere in a uniflow system will cause run problems, whether or not you are running muffler pressure.
Looks like you are about to start testing! Good luck!
Dave
Topic: Need Suggestion on Fuel Tank (Read 2326 times)