Technical rough idle comment

[bogeyman]

hello

i got my second uno fire last friday... pretty neglected, spent the whole weekend on it, but it's not a bad car after all.

anyway, it idled really bad... many unos have this problem, i see?
i've done following things to rectify it:
-regaped the plugs (need new ones)
-disconnected ign. advance hose and sealed it (diaphragm shot, will do like this for now)
-disconnected and sealed a hose running from back of the carb to back of the air filter housing - not sure what it's supposed to do - helped quite a bit
-adjusted idle mixture
-adjusted idle speed
-oh yes, i cleaned the carb a bit... residue from valve cover vent messed things a bit...

now idle is quite ok, cold and hot... btw little car runs like crazy, it's pretty fun to drive, as you surely know
seems to be more fun than IE i had a few years back...

 

[alexGS]

Good work!
I think that disconnecting and plugging the vacuum advance probably made the most difference? However, I think it will hurt performance having less advance (I could be wrong, though, since the vacuum drops when you floor it anyway.)

I reckon the ignition timing as standard (with the vacuum advance working) gives way too much advance when idling. I think for a smooth idle you need about ten degrees - standard Uno tends to be 16 or more. Coupled with the weak mixture, it's difficult to get it smooth.

You may just like to try drilling out the carburettor idle jet (the small one on the short brass tube with the slot-head having a small hole). I have drilled several out to 0.55mm and I find it makes an instant difference. Even with no other adjustments, the engine runs smoother at idle (not much difference above idle, but still...)

You can buy tiny drill bits from an engineering/tool shop, and hold them in a pin vice (like a jeweller's screwdriver but with a jaw, often used for drilling printed circuit boards so try an electronics store like Maplins?)

BTW I think the pipe you mention is the oil vapour separator pipe (the air filter housing has a connection from the cam cover at the top-left corner, the design of the housing is supposed to form some sort of vapour trap which gets let into the engine at open throttle positions). It probably does no harm to close it off, but I can't see it making much difference unless perhaps it was hooked up to the wrong tube on the carburettor? Has someone swapped it with the vacuum advance connection by mistake?

-Alex