86gts misfiring badly low revs

[NiceOne]

hi my 86 gts 1.8 running with a weber 32/34 dmtl carb is stuttering/misfiring at low revs, it is doing it hot or cold and is practically undrivable until you get into higher revs and boot it. If i have the choke on it seems to help but is by no means perfect. if driving down the motorway it struggles to get to 60mph and seems like it wants to stall.
The car idles perfectly with the choke out and has been running perfectly until yesterday, it worked fine in the morning and came out to it in the evening started driving down the road and after about 5 minutes i noticed the problem.

There is plenty of fuel getting to the carb, the fuel filter is clean, the plugs, leads, dizzy cap and rotor arm are only 6 months old

Could someone please point me in some sort of direction with this, it seems a strange one, i am gonna get one of the weber carb refurb kits, do you think this would help, cheers

Shane

[Funky Diver]

Check the rubber grommit/seal under the carb, that is likely cracked and needs replacing. Sounds to me like there's air getting in after your carb, so you're not getting an adequate fuel mixture.

[NiceOne]

Ok I have taken the carb off today and checked the rubber mount which is absolutely fine. Should there be a gasket between the mount and the manifold and the mount and the carb, cos there wasn't. Can anyone give any more suggestions please

[Funky Diver]

Have you checked the vacuum lines to the dizzy, particularly advance retard, etc. If they're letting in air, you aint gonna get the vac advance when needed... which will throw your timing right out.

One test you can try... pul the vac line off that goes to the dizzy... and suck on it with the engine idling, so you're effectively sucking the distributor. It should change the engine note. If it doesn't then there's either summat wrong with the vac advance unit itself... or the pipe work. The pipes and fittings are coppers to replace (comparatively speaking).

The reason I'm following this route is that it sounds like your engine is running either too rich or too lean (I can't remember which) at low revs... ergo low power at tick over... but higher revs, the timing advance is effectively correcting itself.

[MikeH]

My first though was an air leak too... if the rubber carb mount isn't split, then check the servo and vacuum lines, as already said. Any hissing noises around the carb/filter/other parts of the intake tract? If you spray the manifold/vac lines with WD40, does the idle speed and engine note change?

[Nate]

If you spray the manifold/vac lines with WD40, does the idle speed and engine note change?

you should use carb cleaner for this, not WD40. carb cleaner evaporates off quickly. wd40 stays there, attracting dirt and rotting the rubbers

[NiceOne]

im in the process of servicing the carb at the moment because it definately needed doing, i shall be changing the rubber mount anyway, but there was some wheezing coming from the carb when the engine was off, i dont know whether it should be doing this. But i shall check for leaks in the vacuum system if none of the above work, cheers i shall let you know how i get on