QJet starving at WOT?

I have the stock QJet on my Stage 1 which has performed faultlessly in all the time I've owned it (2.5 years) but lately about 2 seconds after flooring it all the power vanishes until I back off.
I get the initial kick in the pants and roar of the secondary opening, 1 or 2 seconds of full power and then blah...

I suspected fuel filter or fuel pump, both replaced wiithout change.
Float level is correct.

Not sure where else to look.

Any suggestions appreciated.

 

I would start at the fuel tank:

1. Remove it and clean it
2. Replace the fuel sock
3. Add new rubber between the tank and fuel lines
4. Replace the fuel filter in the carb

After that if you are still having issues I would add a new fuel pump.

 

Thanks,
will try each of those.

Have already replaced the fuel pump.

 

Assuming your fuel bowl is full, you should get at least 10 seconds of full throttle before starvation.uzzled:

With the engine off I would remove the breather,
hold the throttle full open,
then push down the secondary air blades.

Look to see if the bar between the blades rises as you push them open.

There is a small, thin, plastic cam on the shaft that breaks in two and causes the secondary needle valves not to open.

The secondaries open up and dump a huge gulp of air with no extra fuel...

 

The secondary bores have pull-over enrichment tubes which are fed by wells on each side of the float bowl. Next time you have the top off the carb, check to see if these wells are full of fuel. There is a tiny hole on each side of the center bowl which feeds these wells, and they can get clogged with debris over time.

The other suggestions others have mentioned should also be followed: fuel filter, secondary rod cam, etc, should also be checked. I'd also suggest checking the needle/seat to ensure there's no debris blocking the fuel passage.

 

Thanks for all of the advice, will be tackling it again tonight after work.

 

Sorry for not updating this earlier.
I found the problem.
One of the previous owners had fitted another fuel filter, hidden high above the driveshaft and painted over in black, i just didn't see it.
Pulled that out and it ran perfectly.
Cut the metal case filter open and found it full of crap, collapsed filter media and mud.
Flushed the system, been running fine for years now.