912 ULS Issue on takeoff

Richard, thanks for that, yes i can get 5200 RPM on the take off roll,

Michael Shewan wrote:

Ken, there is a vent pipe that comes out the top of the tank next to the return line, that then routes down and out on the bottom of the fuselage. 

It sounds like the venting system is very straightforward. Still, I would try to confirm that it is properly venting the tanks in all attitudes, since the problem as described could be partially related to attitude.

Great tip, I will go check that out, might be an issue I had to replace the fuel tanks a few months back, I am also thinking of stripping and rebuilding carbs over the winter months, cant do any harm and rules out another possibility. 

So checked both the fuel return line and also the vent pipe, both are clear (blew compressed air through). After that did a few fast taxis to get the temp up (80c) then left it for 10 mins just sitting. Tried to start again after that and was very tough to get it going, which is unusual, strong smell of fuel so presume that its over fuelling? No choke used on the second start up, after i did get it started did 4000 rpm to check both circuits, all good, another few fast taxi's and also full power (5200 rpm) with the brakes on, sweet as a nut.....

Strainer in fuel tank clean, fuel filter clean, no water in the gasculator.....I am confused...

Michael, why did you replace the fuel tanks? Also, are you certain your cold start (“choke”) circuit is closing completely on both carburetors? Check those linkages, levers, and springs.