Fuel delivery problem
 

Ok the motor is broken in and runs well enough.
One problem when the motor is WOT is that I have large bubbles in the fuel line. Actually I would say that there is a break in the delivery of fuel to the carb. Not foam or bubble but large gaps. When I reduce the throttle to about half the fuel delivery returns to normal. Checked all the lines and tank and I have no holes. Maybe it’s vibration but I thought this would be characterized by a lot of small bubbles(foaming). Of course many small bubbles that combine make a large bubble. But I don’t think this is the case. Could this be a pressure problem at WOT?

RE: Fuel delivery problem
 

Where is the fuel tank vertically in relation to the engine? If the tank is too low it can cause that problem. I had a similar issue with a os .46FX in a Hobbico Spectrum. I put a one way valve in the fuel line and it runs like a champ. I don't know why it works, but it does.
Here is a link from tower... I think I picked mine up from the LHS for a couple bucks...
It also makes a nice spot to re-fuel from.
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXG850&P=ML]http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXG850&P=ML[/link]

RE: Fuel delivery problem
 

You state that you have bubbles in the fuel line, but is it affecting the way the engine is running? You've already touched on one cause, vibration. Make sure that the fuel tank isn't touching the frame of the plane. If so try to isolate it with foam. Also check to make sure that you don't have a leak in the fuel system. An easy way to check it to pinch off the fuel line and blow into the vent line so that there is some pressure in the tank, and then pinch that line too. If you hear air escaping, or there is no pressure when you release the line, then you have a leak somewhere in your system.

Hope this helps

Ken

RE: Fuel delivery problem
 

It will be fuel foaming. BUT Also you dont say what the fuel level is when this happens. If it is below 1/2 tank check the pickup tube in the tank as it could have split or been cut, especially at the end of the brass tube that goes through the stopper.

Cheers.

RE: Fuel delivery problem
 

Hi RCKen I've checked out the tank pressure as posted. First with a small amount of air pressure blown in and pinched off for around 3 min. Then tank and lines held, tried again with more air and again it held. I've also put some thin foam between the firwewall and the fuel tank. I think this also takes care of the possibility of a split hose as mentioned by The Ghost. Too late to try it out again tonight. Don't think the neighbours would appreciate it.
If this doesn't take care of the problem I'll try coolbean's suggestion. Hopefully the local hobby shop will have it in stock.
Thanks for the troubleshooting.