SlickCE

I noticed that when running at full throttle ( initial run in) that there is a steady line of bubbles in the fuel line. When I drop to 3/4 throttle the bubbles go away.

I have no room to insulate the fuel tank from vibration in this Superstar 60 so I am wondering if this is one of those normal things unless you buy a certain kind of clunk or something.

Also I set up the initial rigging on the throttle to have full operation from the servo, from full open down the throat of the carb to full closed down the throat. I have noticed that no matter where I set the trim I can shut the engine down with the throttle, even if I set the throttle trim to half throttle..

What am I doing wrong please? ;(

C_Watkins

My Feedback: (10)

1st problem... Get rid of the bubbles, whatever it takes.
You'll never be quite happy with the performance if you don't.
Since this is an initial run-in period, you could also run it too lean and fry it.
If this engine has a remote needle valve, start there. Replace any O-rings on the
needle, make sure the tubing fits TIGHT, or cut pieces of tubing to slip over the
existing tubing at the connections, to ensure tightness. Make sure you have no
pinholes in any of the tank plumbing, but if bubbles are only between the needle
and the engine, and not in the line to the needle, then it's the needle assembly at fault.
(Of course if they're in the entire line, all the way from tank, you'll have to
find a way to insulate it better, or switch tanks if you need to. Bubbles=bad.)


2nd problem...

Either use the EPA (end point adjustment) feature on your radio, if equipped,
or mechanically adjust the throw on the carb. With full UP throttle trim, and full
DOWN throttle, you should have a small opening... enough to let it idle.
It should only shut down with the throttle stick when the trim is ALL the way down.
I noticed this is the initial run-in period... it may take awhile to get a totally reliable
idle anyhow... but it should be able to at least sustain a fast idle if adjusted properly.

SlickCE

The bubbles seem to be coming from the tan k itself, I traced them while running and they first appear at the tank.

On the throttle.. I set it to shut the carb throat fully at full off.. I will have to readjust it to have a small opening at full off without trim tomorrow morning..

Thanks for the help so far

causeitflies

Do the bubbles start "at" the tank or "in" the tank? If your fittings are all secure, it sounds like vibration is causing your fuel to foam causing the bubbles. If there is no room to isolate it with some loose fitting foam you may have to go to a slightly smaller or slimmer shaped tank.

Make sure your engine is tight on its mount and is not causing excess vibration. A badly out of balanced prop will also cause excess vibes. If all else fails add a few drops of Armorall protectant to your fuel jug. This will act as an anti foaming agent. ONLY A FEW DROPS.

tinman

My Feedback: (13)

sounds like the tank may be leaking. i would redo all the lines and be sure the tank stopper is tight.

Montague

It sounds like fuel foaming due to vibration.

You can sometimes reduce the effect of the bubbles by putting a fuel filter in the line as close to the carb or needle as possible, to kind of filter out the bubbles. A few drops of Armorall, as mentioned above, will work too, though too much will cause your glow plugs to stop working too soon. (the silicon will bake on the element, preventing the reaction between the element and the fuel). The best solution is to reduce the foaming by using a smaller tank with padding, or balancing out the engine/prop/spinner a bit.

Many engines can be made to run smoother by mounting an out of balance prop with the heavy blade 180degrees from the piston, so that it basically adds to the crankshaft counterbalance. Most engines are a bit light on the crank counterbalance and this helps balance the whole system.

I didn't see what brand of engine you have. Some engines idle well out of the box, but most will need some break-in and will idle a lot better after they have been run for a bit. Set up the carb as the guys above mentioned, a stable idle at full down stick and full up trim, and an engine kill with full down trim.

SlickCE

I noticed when I got to the field and picked up my plane that it sounded like the clunk was free inside the tank. I then pulled the tank and found the hose had somehow stuck to the top of the tank so the clunk was not on the bottom of the tank..

I will run it again Friday.. sure hope this is the problem

I am kind of wondering why the clunks in planes don't use a wool felt style pickup filter like chainsaws do????

gr8johnson3

i had the same problem. i replaced every inch of line and clamped it everyplace possible. no more bubbles.

SlickCE

I found the fuel line for the clunk had somehow gotten stuck to the top of the tank, so the clunk was only hanging down about a third of the way in the tank..

I would have clamped everything, but the outer diameter of the lines inside the tank seem to be smaller than normal.. guess I will replace them sometime soon to get rid of the no clamp problem.. The bubbles went away once I fixed the stuck line... and the adjustment now holds true...