Occasional top-end miss: Fuel or ignition?

[Stanley]

This shows the effect of lowering the mix nuts after each run. First run red, then green, dark blue, violet, light blue, and last brown. About 5 1/2 turns down on the last run, still "running on empty". Torque falling off accordingly. Floats approx. stock ht., F. press. steady, about 3.7 to 3.9 psi (don't remember exactly).

Raised the mix nuts up some before I drove back, and another half-turn today - using too much gas.

[madkaw]

Adjusting the mixture nuts does not help your WOT issue. They are for fine tuning. If the fuel is not available there's nothing to adjust. Not sure why you haven't adjusted the floats yet, but at this point maybe you should give it try?

[Stanley]

The week before the dyno I Checked the floats, front one low so I adjusted it up to stock height, rear was OK. Have a pair of sightglasses to check fuel ht. (at no-load). Should have hooked them up at the dyno. Hindsight 20-20. However, post #23 might be correct, so I'll try raising both bowls 2mm above stock ASAP.

Also the needles and nozzles are new (six months old). The old nozzles were shot. MSA didn't have 72's so I got 71 nozzles with the N-27's, as they recommended. Wonder if there could be an issue with that.

Also wonder if fuel pressure could be an issue, even though it's OK per FSM. Maybe it needs a little more to keep up? According to the Ztherapy video (in the British SU section) fuel pressure affects A/F ratio. There was a post about someone needing more than stock fuel pressure, but I think they were racing, maybe bigger engine.

[madkaw]

N-27's will run plenty rich enough. Don't worry about fuel pressure for now. More effective would be a volume test of the fuel pump.