I had an interesting fuel flow issue at the RCU race in Tri Cities. It gets way, way hotter in TC than it does in western Washington and as the day went on i kept richening up the needle, but the boat had all the symptoms of being lean (black holing glow plugs, motor really hot) but according to my Boris meter it was ridiculously rich-should have just been blubbering. The boat was screaming but I finally jumped the fence and it died in the last section. Long story short. I couldn't get enough fuel through the medium size tubing between the sump tank-needle-carb. I think the fuel had expanded so much from the heat (close to 100 degrees) that the motor was starving due to lighter fuel density. Went to large size tubing, reflowed back to my setting from the morning and went out and won the connie. The proof was that I loaned one of my motors to another racer and they also had problems until they went to larger fuel line.
In some ways I guess it's a good thing as I have been working on getting my motors to flow more fuel for higher RPM w/o giving up torque, so it makes sense that larger tubing would be needed. Never would have known in the Seattle area because it doesn't get that hot. The heat definitely has a way of bringing tuning issues to the surface.
The flow issue? Well, the flow meter was pushing air through the needle-not fuel. I'm guessing that was the reason for the rich indication. Once I used the larger tubing the flow meter numbers became relevant again.
