Erratic Idling on 1800 Clipper with Weber

My 1991 Clipper had a Weber carb conversion a couple of years ago and has been running like a dream until last month.  The idle speed has become erratic, sometimes around 1,100 rpm, sometimes around 600 rpm (very lumpy!) and sometimes around 900 rpm (about where it should be).  When it's around 900 rpm the tickover is a bit all over the place and varies by a couple of hundred rpm.  This is a bit frustrating as I ditched the old Pieburg carb because of poor running.

The fuel filter is clean, I wonder if the mixture is a bit off? It has recently come back from an MOT and wondered if some has messed aorund with it to get it through the emisions?  


Is there anything I can adjust to get the idle to settle again?

Hi it does sound like mixture m8

 I know my weber does this when its running weak. To set it to baseline, first swich off engine. Locate the mixture screw. Now with a flat head screw driver slowly turn the screw in. (Clockwise) till it stops. Note the postion of the screw driver and then turn the screw out two full turns.(anticlockwise). This is the base line setting for the 32/34. Ideal position.


Taken from redline weber

Simple Rules for low speed calibration

If the mixture screw is more than 2 and a half  turns out then the Idle jet is too lean (too Small). When the mixture screw is less than 1 and a half turns  then the Idle jet is too rich (too large). These assumptions are based on the fact that the speed screw setting is not opened more than 1 1/2 turns. If the speed screw has to be opened 2 or more turns then this is also an indication of a lean condition usually requiring greater change. At times it may appear to be showing signs of richness or flooding it is really a lean condition. See pictures and notes in the tech 2 article supplied in the kit instructions, view and please understand the need to keep throttle plate as near to closed as possible so as not to prematurely expose the transition holes. This is what causes the visible rich condition, and confirms the need to increase the jet size. JET KITS are available if needed.

Info taken from CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT


Start your car and see if if it runs any better. If it does then your on a roll.IF it does not then you have somthing wrong. I would check

All jets, by taking them out and give them a good clean

Split Rubber flange. Re-new part. about 15 quid from GSF carparts

Check Vac pipes and also that its bolted down ok.

Hope you get it sorted
Regards
Andy

Check all Vacuum pipes

Thanks for the replies, I will give it a go this weekend in between the house renovations!  Old cars and houses, endless fun!