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High idle speed on 13/60 stromberg


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Got the car warmed up properly for the first time since purchase yesterday and my idle revs were about 1100, throttle stop was screwed right back and the choke quadrant was clear. Could not get it to slow down. Unscrewed damper a touch and it reved even higher!

What is worn lads? seriously getting me down now.

Do not suppose there are any old triumph specialists just north east of Hadrian's wall :)

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High idle is often caused by air leaks. It only needs a really tiny leak. However, increased idle speed as you unscrew the damper (I presume you mean the black plastic dashpot cap) seems odd - it might suggest wear in the upper body or piston.

Do the usual carb condition tests first:- check the piston lifts cleanly and drops sharply (makes a clonk); check the throttle shaft rotates smoothly and returns fully, and that it has no significant end- or side-play.

Is there any movement of the carb body, if you try to lift it? Obviously don't try to jack the car up on it, but you can give it a decent tug. Movement suggests loose fixings, either the manifold to engine or the carb to manifold. Either would cause air leaks.

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apart from air leaks in the breather system it may have a diaphragm problem 

it may be fitted with the location lugs out of place , worn throttle spindles can be felt with s wiggle but unlikely to raise the idle that much 

remove the top cover have a look if the diaphragm is all wrinkled /baggy wash it in petrol to reform it

the holes in the base of the air piston must be facing the engine side 

i guess this is a CD150 with what  call thames barrier type choke arrangement 


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Thanks guys. I replaced the diaphragm last week and am happy it is 'in its slots. there is 'tiny' movement in the spindle but nothing much at all, Piston drops well and no movements anywhere. Guess it is a worn body then. Just like mine!

I guess with 126k (engine only has 26K) the CD150 is nearly 50yrs old so will need attention. What is best way to refurb? can I get parts and DIY?...............the list is getting longer, my temper shorter, my pockets emptier and my wife is getting ignored :)

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you must first be clear there are no air leaks from  manifolds or breather systems !!!!!!!!!!!!!

if nothing else a squirt of engine oil on the joints or any expected wear leak will get sucked in when idling if its a leaker 

many suppliers have some parts  Burlen fuel systems probably the most 

as for wear the spindle wears a lot more than the body and easy to replace 

i have used the carb exchange in leighton buzzard  good guy no frills or bullsshine   http://www.carbex.demon.co.uk/

some do lots of shiny but the rest is problematic , got pleant of tee shirts for sorting hi costing cock ups 

youre a bit too far away for a visit 


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Just double checked and maybe the diaphragm body lug was a touch out. Hey! I have a tickling stick on the carb!!! No need to take air filter off and use a thin screwdriver.  Very handy. No mention of that in the manual. No chance to test it when warmed up as it was raining and I'm not waterproof!

What exactly is the breather system?

The vacuum pipe to distributor seems a bit manky, might replace that.

Time for T again. Enough today :)

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breather system the hoses and any valve starting at the rocker cover and ends up into the manifold often with a smiths emission valve in between

dont think 13/60 had a smiths valve just a hose from rocker to filter 

 lifting pins are  fitted to all SU and Strombergs  until emissions started to creep in to designs and twiddling was made difficult

if you remove the air filter you wreck any hope of them showing wahts going on as you have upset the  depression in the carb, and mixtures are all upset 

the trick with lifting pins is touchy feely ,, lift to just contact the air piston inside , then raise the piston a few mm  if you yank it up it will just stop 

so a small light lift 2mm 

you are looking for a hint of change if revs pick up +50 rpm for a short its rich  if it drops 50rpm its weak   if no change   its fine

so get the filters on and tickle it........... its not a wam bang thankyou job 


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Yes Pete, gotcha. The rocker cover has a breather to air filter but it is not air tight. That is just emissions 'control' surely, not related to mixture ??

I have checked mixture via about 1/16 inch lift and all is well. I have sensitive finger tips and can feel the piston no problem :)


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so its a std 13/60 open breather , you cant pre judge whats been fitted over the years , many engines have a sealed breather which is fed to the manifold  so any air in ups the idle 

you dont have that complication 

it could be lacking adjustment with the butterfly not centralised or even worn side edges to the disc 

a new spindle and throttle plate might be on the cards   


have you checked the timing  , over advanced will increase idle speeds 


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