(G) Jet-up to fix FIRE idling

Yeah sorry but I think this is a big deal - I sorted the greatest pig-of-a-job I've had in ages. 1.0 FIRE (carb) engine, barely idling, more like bucking and kicking around the engine bay. You know the type - mixture adjustment screw seems to make no improvement, just even worse...

Swapped ignition parts etc. with no improvement.

On the good advice of a specialist, I jetted-up the carb. The idle jet is the one with the larger slot-head (tiny hole in middle). The jet itself pulls off the screwed-in holder. It was a '47', and I had a few other jets out of Uno and X1/9 double-barrel carbs. Basically I had a '50' and a '70'.

Being the sort of person that I am, I stuck in the '70' (even though that was designed for a larger engine and for high-speed progression onto the secondary barrel) and reassembled airbox etc.

Result - suddenly the mixture screw has an effect, suddenly the engine is smooth and starts nicely with the choke instead of firing and dying.

Theory - wear in throttle spindle allows more air into an already-lean setup (for reduced emissions). Larger idle jet = more fuel at low loads = theoretically higher fuel consumption but in practice, smoother running and easier takeoffs probably use less fuel.

Just a hint, though really I owe Maurice Thomson (Te Awamutu, NZ) a big thanks, and probably shouldn't divulge his secret (except that I knew this trick before from similar improvements on an Uno 70...)


-Alex