The continuing saga of my 4*60 and bubbles in the fuel line.

I can't think of anything else to do. So far I've done the following to try to remedy this problem:

1.) Yanked out the old fuel tank, replaced with new tank and new lines
2.) New foam around the tank
3.) Installed a fuel filter
4.) Balanced prop.
5.) Rechecked engine mount and tightened up all hardware


I'm still getting bubbles....and I've no clue what to do from here. Any suggestions? This thing is driving me crazy.

BTW I'm running a Saito 100 just in case that matters.

Do you have a fueler valve on your suction line ? I used to have alot of problems with these but since I switched to fuel dots no more problems.

Some filters that come apart cause problems, switch to Sullivan crap trap or remove altogether UNTIL you get it sorted out.

???????????????????

Have you seen the bubbles coming from the tank. You're sure they're not coming from the carb? My OS 120 FS did the same thing. It was caused from the intake valve opening too soon. I could have sworn it was coming from the tank till I put it on a stand and watched it.

Yeah...I'm pretty sure it's coming from the tank. I broke this engine in on a test stand with no problems. Once mounted on the 4* is when I started getting the bubbles.

MountaineerFan36,
Are you completely sure that no part of the tank is touching the wood of the plane. Maybe the front outlets on the tank are touching the frame of the plane? From what you're saying it sure sounds like something is still in direct contact with the fuel tank that could be still causing the foaming.

Ken

if the nose of the tank is touching the firewall that will do it. I have had this happen and just pushed the tank back a little and the bubbles stopped . is the stopper in the tank tight? fuel lines tight on the outlet to the motor and the fill, and pressure from the muffler? you know there are anti bubble klunks also available.

Ken:

That's possible. I'll double check to be sure. It is such a tight fit to get the tank in with the foam that some of it may have "scrunched up" around the front of the tank causing it to come in contact witht he firewall. I'm trying to avoid cutting a hatch to access the tank...but it may be the only way I can be sure the tank is properly installed.

Wow...I never knew these existed..thanks for the tip! A quick search on Tower and I found one.

http://www2.towerhobbies.com/cgi-bin...XF25&P=ML#tech

Seems a little expensive for a klunk...but I've spent more time than I care to say trying to solve this problem. I'll repack the foam and install one of these baby's...hopefully that will solve the problem.

Check to make sure the tank isn't touching the frame before spending the cash on the new clunk. If you have problems with the foam shifting when you slide the tank in you might want to spray a little bit of 3M 77 adhesive on the back of the foam. This will give enough "stick" to secure it to the inside of the plane, but you can still get the foam out later if you need to.

Hope this helps

Ken

Are you sure the tank isn't leaking somewhere and letting in air?

Anything is possible, but this is the second brand new tank that I've put in with the same results.

It is not unknown for brand new items to be faulty. just because it's new, don't mean it's any good. Try blocking of the fuel tubes, but leave one tube unblocked so you can blow into it. Put the tank in some water and blow into the unblocked tube. If there is a leak any kind, anywhere then you will get air bubbles comeing from the tank. I don't no if you have already tryed this or not.

I had a similar problem with an RC Monster Truck I used to race and after ages of mucking around I fitted fuel line clamps over the fuel lines where they connected to the carb and remote needle valve etc.
If your lines take a fair bit of force to remove them from the carb nipple etc when you pull on it then this probably isnt an issue. My lines would pop off easy if pulled gently. I was using cheap nasty fuel line which was most likely the cause.
This clamp was made out of a small piece of fuel line which you open up with a small pair of needle nose pliers and slide the fuel line through. Then just push the line and clamp over the carb nipple and exhaust nipple etc.

Worth a shot if you have tried everything else.