Originally Posted by grizz1

Hi Felix,

That sort of run time points to a tuning issue, most likely bottom end needle.
Check your idle gap is only .5mm to .7mm and that you don't have a rich bottom end compensating for an overly large idle gap.
With the long low speed needle on the GO carbs, the bottom end needle controls fuel flow right through the power band, so if your rich here - no run time.

If you can get a hold of a Werks 2058 pipe, run this on your GXII Plus. You will be amazed at the difference from the the stock 2103 and other pipes you have tried. More power all around, and increased run times.
Guys here running that pipe on the GXII Plus are seeing 8.5 min to 9 min tanks no problem.

If your only running 25% fuel, you can play around with shim stack too. This will increase power and run time a little.
Drop out .1mm or .2mm of head shims and see what difference that makes (tuning window will be slightly decreased).
These engines are traditionally reasonably low compression designs, but if you start blowing plugs, revert back to stock shim stack.

Try the tune and pipe first though