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Trouble getting a low idle


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Hi everyone.


Vitesse Mk1 2Litre


After removing the jet orifice holders on both carbs to drain the float bowls I now cannot get it to idle below 1,000 revs.


I centralized the needles as usual and the air valve pistons are dropping  with a small clunk onto the bridge after lifting them about 5mm.


The throttle is returning to lower than its usual adjustment, as I have backed off the screws so they aren't making contact.


I haven't altered the mixture screws or anything else.


Also since this, the car is lacking on acceleration and this seems to improves when the choke is pulled out.


The dash pots have their usual amount of oil (The air valve pistons start to resist after lifting about 5mm).


So I guess there is air getting in. Could this be related to what I have done as I don't see how.


Any advice much appreciated, cheers, Dave 






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You may not have one but most mk1 had this


where does your breather run anything connected between manifold and carbs needs control.

If its an open breather and not fed to the manifold its not affecting carb settings

if its a sealed system it needs a smiths valve or certainly no air allowed to get in from the oil filler cap

or any other crank case area. Or failed rocker cover gasket etc.


Any air in will raise the idle with no control from the carb settings



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Hi and thanks a lot for getting back with info.


I know what you mean now.


Mine just has a rubber/plastic tube from rocker cover to air filer box. I added a couple of jubilee clips to each end of this a while back to eliminate air getting in.


One other thing that happened since this idle issue. Once when starting from warm, as soon as it fired up, the revs when very high immediately. I switched it off and it didn't happen again when I started it a few seconds later. Don't know if related.


Cheers, Dave 

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ok so thats an open breather it wont affect the idle 



have you checked the choke fast idle cam has a small gap between the cam and the adjustable tappet screw it operates when you pull the choke

the spindles on the choke can stiff up and not fully return ,  ( guess this has what i term thames barrier type choke )


time to slacken the co joining rods on chokes and trhottle plates


make sure throttles are set so screw just touches its stop casting and wind in 1.5 turns for each carb then nip the link rods

same make sure chokes are fully off and the levers and the small bias springs are free and return then nip the choke link


make sure the choke cable is not jumping out of its location and making the choke open when the knobs pushed home .

and the throttle cable is also seated , if they jump out and hang on the abutement you rev the nuts off it without knowing why.

often caused by too much slack and if operating the carb spindles the outer hangs up on the baukhead fitting 


just some thoughts



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Thanks Pete. I think the very high revving was due to the cable having jumped out.


I also loosened throttle clamp and front carb butterfly flap was not quite shut off, though I hadn't altered these and haven't listened to air suction balance in different carbs, with my trusty hose pipe and funnel. 


So have a low idle now. though engine won't completely die. Throttle spindles have wear and also I guess the butterfly flaps could wear at edges, allowing air in.


Again thanks for the tips,


Cheers Dave 

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Spindle wearand edge wear are often found, but if youre after reasonable running and not looking for utopia

you should be able to get a basic and reliable result,

worn spindles can improve if you up the base idle speed to around 1000


may get you into a running state , once happy slow her down a bit


its normally the spindle that wears more than the body, the body can be re bushed but needs a

proper jig to rebore the oversize concentric with the throat bore.


so a new spindle might get you out of trouble, its the best fix for the money wouldnt worry too much about plate side wear just now.



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Cheers for that advice Pete,


Something else regarding carb tuning if you don't mind, as plugs are generally pretty sooty around the city and my partner gets fed up If I want to do plug chops on a run .


The washers that are between the the float valve vary in thickness between the cars (one looked about 0.8mm, the other about twice that). The actual valves differ in style and one has a mesh filter on the top that was a bit dirty and wouldn't clean easily, Both have have 1.5mm stamped on them.


Also the float measurement on both carbs is about 21 mm (manual says 18mm). I don't know how critical this is, but I'm thinking it would make fuel levels higher, therefore more prone to running rich.


Also the alloy washers at the top of the main jet assembly vary in thickness, though I guess the mixture screws for the actual jets would just have to be adjusted accordingly to compensate for different base height.


Just wondering if over the years, any washers have been slung in, or if these differences in washers/factory float height settings have been done on purpose to compensate for carb/engine wear.


Sorry to bang on, I don't need perfection, but wonder how much anything too much out can damage engine and also find it all interesting.


Cheers, Dave

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first sooty plugs around town and always accelerating is a normal, as acceleration makes a demand for rich ( due to the dampers)


never use a plug with a R (resistive)  in the suffix our coils wont fire them properly.


the setting for the float held upside down making its close the valve is 18mm from the chamber face to the highest zone on the float 

21 will make the level lower and weaken 


 so then you  need more throttle to drive and hence more soot if that makes sense .


I would prefer the holder washers and needle washers to be the same , the drop of the jet holder has some effect on how the fuel is drawn from the needle position  suggest a kit from your prefered supplier.


I use the carb exchange  local to Me   http://www.carbex.demon.co.uk/    funny little place but if they answer the phone they do a good job with the right parts


many use Burlen, A Turner, etc 


yes some  later or aftersales strom valves have a small inserted filter mesh  .


set the float height by setting the arm , rather than packing the valve ,    if the float has two arms its easy to get it upsidedown ( think weve covered that )


if you fit new spindles sometime make sure the disc is centered and fully closed, before nipping the two screws up


some discs have a chamfered edge to seal the throat, so must be right way round,

dont think yours will be .  just flat /square edge ,  you need to have a close look.



the jet bush washes should be a nice flat finish not scored ,  and the jet  O rings a neat fit or you can pull fuel from around rather than  'up' the jet



dont stop asking , 

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