The flat feeling at lowish revs is usually down to a weak mixture. Raising the fuel pressure will often sort this but is a crude way to cure it. Not all engines seem to suffer from this so I'd guess it's down to tolerances.Fed_up_Stag-owner wrote:Thanks Ramon, lots to work on from your last post. I must admit that I've been out driving rather than fettling (feeble excuse); the acceleration appears to be smoother but perhaps I'm "working around" the flat spot with throttle control. Historical misfire on tight corners (which is where this problem/opportunitystarted) is cleared, and what a great engine for sitting behind in a convertible out in the sunshine.
The common adjustable regs are rising rate types which will do it at the expense of fuel consumption. But you can get non rising rate adjustable ones made for turbo etc engines.
A simple check if this helps is to clamp the vacuum hose to the reg after starting the engine (you'll likely have to raise the idle speed to keep it running) This will give an over-rich mixture - but if it cures the flat feeling proves the point, as an engine will run well with an over-rich mixture.
Clamping the hose raises the running pressure at low revs/lowish throttle opening by up to 8 psi. About 2 psi increase overall usually sorts things, without too much effect on the MPG.
