Sig 4 Star tank problem
 

I recently finished my 4Star. I took it to the field, got some of the bugs worked out but now have a problem with the tank level. I built the tank compartment stock with the platform for it to rest on. However, I built the engine inverted. It is a Magnum 91 4S.

The problem is that the fuel is siphoning into the carb and flooding it. I think I need to lower the tank. The problem is that there isn't a hatch and I will have to cut open the top of the fuselage. I hate to do that to a plane that I haven't even flown!

The fuel compartment is so small and hard to get to, I don't see any other way than to cut open the top. In order to get in there and cut out the platform, I think I will have to.

Before I do it, does anyone have any thoughts on alternatives?

Thanks much!<br type="_moz" />

RE: Sig 4 Star tank problem
 

Been there done that.
Had to do the obvious, made the tank accessable.

RE: Sig 4 Star tank problem
 

I feel your pain,
A rule of thumb I follow when building, and probably mentioned in most engine instructions is to have the center tank level as close to the level of the carb as possible.
I am not familure with your engine, but on some engines you can change the carb location.
Might be something to look at.

RE: Sig 4 Star tank problem
 

On the OS engines I have it calls for center of tank to be 1/4" lower than needle valve.

RE: Sig 4 Star tank problem
 

I've built a couple of 4-stars and a Venture 60 (Bruce Tharpe's improvement on the 4-star 60). I always make a hatch for the tank. It's rare to never have to get at the tank for anything, and adding a hatch is simple.

RE: Sig 4 Star tank problem
 

Truth be known - yea, a tank hatch is useful but not sure how much help it would be for solving OP's problem.

Looking at the pic (4Star60 - assuming that this is the OP's plane as it has a 91 4-stroke) the rear former allows for the removal of the tank. It does not need to be radiused if a tank like mine is used. You will need to pop the tank tray out, narrow it so that it will fit between the doubled fuse sides, and supported with balsa block the set the tray at the new level.

RE: Sig 4 Star tank problem
 

Joe,
Coming back to your original question. I always use 3 lines from my fuel tank. To carburator, to muffler pressuretap and a filler tube that stays plugged up all the time after fueling.
The pressure lineequalizes the atmospheric pressure and makes the fuel flow by gravity if the level of the fuel in the tank is higher than the carb. Which leads me to the conclusion that u have to lower the tank.

RE: Sig 4 Star tank problem
 

A hatch allows you into the tank area so you can cut out the shelf the tank is sitting on. Being able to get the tank in and out is really helpful. With an inverted engine the tank center line MUST be lower then the carbs spray bar. How you are able to get the tank in and out is up to the builder, one of the joys of building but you must think ahead. Sometimes you can just install a new tank and disconnect the one you have. Just a thought?

RE: Sig 4 Star tank problem
 

A "new" hatch on the bottom would be a bunch easier ...

RE: Sig 4 Star tank problem
 

I always build hatches for tanks and othe access I need. Many times they can disguised quite cleverly. Older designs are famous for not having them. I had the 4 star and had a blast with it.. great flying plane.

RE: Sig 4 Star tank problem
 

Is it possible to relocate the tank to over the CG above the wing?  I did that on my 4*, but its a 120 size, so dont know if the 60 has the room for it.

RE: Sig 4 Star tank problem
 

You can place the tank anywhere there is room for it but will your engine draw from that area?? This is one of the reasons I like pumped engines. I have had problems in the past with some planes due to lack of room for a tank, sort of like the plane I'm building right now. I had to place some items in the way of where the tank should go so it no longer fits. I had to place the tank way back under the wing saddle. Instead of fighting it and doing a lot of vodo crap like the last time this happened I switched engines, I went from an SK .91 two stroke to a 1.10 YS. YS engines are pumpers so it fixed the problem. I could place that tank under the stab if I wanted it.
I fixed the last one with almost the same problem by using a bleeder tank in the very small area just behind the fire wall, it worked out very well but took a lot of fooling around trying other things before I hit on the bleeder tank.

RE: Sig 4 Star tank problem
 

Hatch on the bottom of my Swoose.