Hi

My engine (1275) twin HS2s has a fluctuating idle from 1200 - 1500 rpm, if you press/blip the throttle the idle goes down a little or slowly idles down to normal or below normal where the engine wants to stall. Checked the throttle cable and its not binding or sticking.

My guess is running too rich? there's no black smoke when I rev the car or drive it harder than normal or sluggish etc.


Any advice peeps?

mine does the same thing. Im not sure why but was thinking maybe a sticky butterfly
I am going to kit mine when i finally get round to starting my restoration

1200-1500 is pretty high idling for 1&1/4's. How annoying eg does it do this when engine hot or cold (no difference?). The usual culprit I have found with twins is wear in the butterfly throttles (spindles) ie the butterfly discs don't return fully (read close) at idle. You can check this by pressing on the the throttle linkages to see if the idle speed then drops. If not, check the idle mixture by raising jet nuts (anticlockwise looking down from the top, from memory) & see if this reduces idle speed, if so, yes it's mixture problem. Another drama could be rich mixture at idle due to incorrect float chamber levels (fuel levels too high). I think this is the ist thing you should check if the problem is not wear in the linkages. Unfortunately, it could be a combination of things, so you need to go thru the process of elimination, after making sure there's no wear in the spindles and air leaks, etc

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1967 Cooper S - new front bearings to do.
1965 Cooper S shell - Slow progress. No time or money!
1966 Deluxe- next rustoration!
Mk 2 & XJ6 Jags. Less said the better.

I agree with all above - in a nutshell its sucking air or gettting to much petrol.

Check the manifold alignment for leaks as well as all of above. But........ spindle wear is the most likely major contributor

I've noticed at 1st start from cold my idle will be around 1200rpm runs fine
after say 15-20min drive the rpm is sometimes 1500rpm or sometimes around 800rpm
if its sitting on 1500rpm if I press/blip the throttle it kinda goes down slowly
or sometimes the engine wants to stall on neutral or on gear at full stop

Buy ya self a can of Clean R Carb, while the engine is running spray it around the manifold where it meets the head, also spray around the throttle shafts. If there is an air leak, the engine revs will rise briefly!!!

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As others say, it's a symptom of throttle shaft wear.
Barney's twin HS4s do it a bit too, but not bad enough that I'll worry yet.

Pity that Mr SU didn't use proper (ball) spindle bearings and seals, a la Weber and Dellorto...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I reckon the throttle shafts are worn, that's what happened to me. It stopped once i put my new carbies on (they were rebuilt).

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"In two years time your car will be like a lady's clothes, out of date, my car will still be in fashion when I am dead" - Sir Alec speaking to Pininfarina