tower.46 nitro engine
 

[:o]yes can anyone help it seems that the engine runs fine untill it becomes low with fuel about 1/3 left in the tank it sputters but doesn,t stall only thing it won,t idle with that amount of fuelwith a full tank its fine any sugjestions?

RE: tower.46 nitro engine
 

The first thing to check is the muffler fitting. Make sure that the fitting is clear of any obstructions. This is were your tank pressure comes from. Also make sure your clunk inside the fuel tank is not too long. The clunk should come close to the rear of the tank but not touch.

After that, if this is a new engine, start checking your idle needle. Don't screw it all the way in and start from scratch, just start adjusting it from where it is at. Do the pinch test with the engine at idle. It should stay at the same speed for a few seconds, then a small rise and then die. It is set from the factory on the rich side to begin the break-in process. After you lean it out some you should notice a more reliable and lower speed idle setting. After you adjust the idle needle go back and adjust the high speed needle setting the same way, but you should notice the speed rise as soon as you pinch the fuel line.

Also another thing to check is the glow plug. After you start the engine and get a reliable idle, when you remove the igniter, there should be no difference in idle speed or sound. If it changes, your glow plug is due for replacement.

RE: tower.46 nitro engine
 

Also check the location of the clunk in the tank. If it is stuck up against the back of the tank, you will not get all the fuel out and the engine will die. Good Luck, Dave

RE: tower.46 nitro engine
 

I know this sounds crazy but I put a golf ball sized peice of steel wool inside the muffler to raise the tank pressure on a couple I had that was giving the same problem. I done it after gettinbg the advice here on RCU. I was skeptical at first but it worked. You have to use COARSE steel wool.I went through the same thing you're describing, sputtering after 1/2 tank of fuel burned and would not idle which resulted in dead stick landings galore. I later built a baffle out of aluminum for them. You lose just a little power but if the engine won't run with out it what good is it? There is about a 40 page thread in the engine forums on the GMS and Tower engines related to this problem.

RE: tower.46 nitro engine
 

I was just thinking that instead of puttingg steel wool inside the muffler, this might be one instance that an exhaust diverter would be usefull.

http://www3.towerhobbies.com/cgi-bin...&I=LXL378&P=SM

I have noticed on my engines that it will decrease the top rpm, but if you are not getting enough backpressure, it will help.

The problem with steel wool is that it will get gummed up with the oils and not breath anymore.

RE: tower.46 nitro engine
 

Since this is only occuring with 1/3 of a tank of fuel or less, it is not that likely to be a pressurization issue, as you would get similiar results at 1/2 throttle.

So could it be that the vent tubing is pointing in the wrong direction?

What happens if you point the nose of the plane UP when this happens?

Could the clunk be stuck foward in the tank?

Does the tank sit slighly nose down when the plane is level?

Does the clunk NOT touch the back of the tank, which is ideal?



BTW: Steel wool will ignite with the exhaust gasses from the engine fouling up the entire exhaust system. It's not a good idea.

RE: tower.46 nitro engine
 

You may need to pull the tank apart and check all of the tubing, including the brass parts, for pinholes or cracks. If you have a leak in the pick-up tubing, once the fuel level is below the leak it will draw air. The engine will lean out and die.

RE: tower.46 nitro engine
 

Yeah Crossman's idea is my most likely candidate.

I've seen this happen because of sharp edges on the tank tubing.

A small split or crack is formed that is normally submerged when you are running more than 1/2 a tank.

A nose up test at 1/3 of a tank is helpful, and should be done when tuning any engine.

RE: tower.46 nitro engine
 

You might also make sure the tubing is flexing enough to reach the bottom of the tank when the level is low. I have an eight ounce dubro tank that I replaced the fuel lines and clunk in and the new silicon tubing I used was not flexible enough to let the clunk fall to the bottom of the tank, it just kind of hung at about 1/3 tank level as you describe.

RE: tower.46 nitro engine
 

:Dthank to all your input i seemed to fix the problem with the sputtering du to a loose fitting on my tower tuned muffler it was the nipple fitting worked its way loose the way i noticed when running the plane some fuel or bubbles were coming out of the vent tube near the muffler. i guess check the obvious first ?

RE: tower.46 nitro engine
 

Glad you found the problem. A loose pressure fiting will give you the same results as one that is partially clogged.

While you are at it, and since you found something loose. check/tighten all of your head bolts, and crankcase bolts. Loosen the crossbolt that holds the carb in and pinch the carb down while retightening the crossbolt. This should eliminate any other leaks before they become a problem.