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Idle Setting


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#1 ln1gaw

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Posted 14 May 2019 - 01:59 PM

Hi Guy's,

 

I'm new to this forum and looking for a bit of advice on setting the idle on my 1989 Mini Mayfair 998cc. It's fitted with a single SU H4 carb and for some reason it has always idled too fast, even though the idle screw is screwed completely out so no adjustment left. The butterfly would appear to be completely closed and there is slack in the throttle and choke cable and yet the engine still manages to idle and too high. I'm not sure if the mixture screw can affect the idle to this extent but some advice in setting that up would help too. I.e. should the mixture screw be turned up so far as the engine stalls and then turn in the idle screw?

 

Cheers in advance on any setting up tips.



#2 ChrisRuffell

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Posted 14 May 2019 - 05:38 PM

Hi Guy's,

I'm new to this forum and looking for a bit of advice on setting the idle on my 1989 Mini Mayfair 998cc. It's fitted with a single SU H4 carb and for some reason it has always idled too fast, even though the idle screw is screwed completely out so no adjustment left. The butterfly would appear to be completely closed and there is slack in the throttle and choke cable and yet the engine still manages to idle and too high. I'm not sure if the mixture screw can affect the idle to this extent but some advice in setting that up would help too. I.e. should the mixture screw be turned up so far as the engine stalls and then turn in the idle screw?

Cheers in advance on any setting up tips.


Have you checked ignition timing? Overly advanced will make it rev slightly more.

#3 unburntfuelinthemorning

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Posted 14 May 2019 - 07:10 PM

It's commonly due to wear on the throttle spindle and/or spindle bushes.  Excess air gets sucked in through the bushes.

 

Could be over advanced timing too as above.

 

Incorrect mixture adjustment will only slow it down.






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