Originally Posted by Corse-R

Ok. You could have the LSN leaned as a hell but if is too lean could mask a too rich HSN, hence you poor runtime. Give us more details of your car when running only 4 minutes, starting from engine, fuel, chamber height (measure it with the crushed solder), ratios, wheel measurements and of course, track size and type, you could have there somewhat wrong.

Another way or gaining runtime is going from conical to straight tube manifolds, but you'll lose power. Check if someone can bring you a Nova 9886 pipe and a short straight manifold and see if runtime improves too.