Right lads / lasses I have a tricky issue on my MK2. I was having a few minor running issues then noticed the carb mount was split and whole carb / air filter assembly moving around lots. I've replaced this now but the car is hunting and possible misfiring. It won't idle properly without a little choke - if I push the choke in all the way it stalls.

 

At speed it runs OK especially with a bit of choke. Before I replaced the carb mount it didn't need choke to idle but wasn't quite idling right. 

 

I've checked and all plugs are getting spark and removing each lead in turn the engine struggles so I don't think it's ignition unless. 

 

So either I've cocked up the carb mount install or maybe there is another vacuum leak or carb problem. The line between the dizzy and the air filter is a bit cracked so will try replacing that.

 

Any ideas let me know thanks! 

Sorry not the line from the dizzy that's cracked, can't remember where it comes from but is the one that goes to the air filter. 

Note my car has a Weber carb with manual choke (not correct for this 1990 car but seemed to work well when I bought it)

If engine will idle, you can find a vacuum leak by spraying carb cleaner or cold start (diethyl ether) at the outside of carb and vac lines and listening to engine sound.

 

The former spray will slow engine, the latter speed it up.

 

Over-tightening the base mount nuts can pull the captive threads out of new mounts, especially as these don't appear to be as well made as 20 years ago. Febi and Birth SPA appear to be good still.

 

How clean is the fuel filter?

 

You may have coincidental blockage in the idle circuit.

(perhaps from disturbing the fuel line or air filter).

 

Maybe just partially blocked in the Weber idle jet (smallest hole at 0.4mm ish) , or at the mixture screw and passage. Unscrew idle jet and blow through it. Count the clockwise turns and make a not of how many, to fully screw in the mixture screw (gently) at the base, then unscrew it and pull it out (careful not damage the o-ring) then blow air down a tube into mixture screw hole so it bubbles in the carb well.

I use keyboard cleaner can, but have used a bike pump and silicone tubing.

Refit mixture screw to bottom and unscrew again by the noted turns. Refit idle jet.  It might need 1/8 turn more anti-clockwise for cold weather.

(I'm assuming it's a Weber twin choke DMTL or DMTR on a 1.3, not a single choke like IBF or ICH on 1.0 which have idle air bleed screw to adjust).

 

Find Redline's Weber Lean Best Idle method to set it best. 

 

Edited 31 December, 20214 yr by dvderlm

Not sure which engine/ carb set up you have, but If the thin pipe to the air cleaner is cracked that will introduce air, though I wouldn’t have thought enough to stop it idling altogether.You can plug it at the carb end to discount it.

 

If carb has an idle cut off valve make sure the earth strap is fitted between the carb and the cylinder head, if this is detached the engine won’t idle and will run rough. My 1L HZ with the Pierburg had this problem when the crimp became loose and detached itself. I initially thought the flange had split.

Edited 31 December, 20214 yr by mk2tastic

Great info thanks all. It's a '1.05' HZ engine with Weber 32 TLA (with manual choke conversion)

 

 dvderlm you were right in that it seems to have been a blocked jet or fuel filter. I cleaned out the filter (it's a reusable type) and blew through the idle jet then ran some carb cleaner through the carb inlet and its idling much better now and doesn't need choke once warmed up.