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Idle increases on its own


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Fitted new coil, dizzy cap, plug leads, electronic ignition module inside dizzy cap etc. started car using choke. All fine. When warm with no choke idle drops to 500 and goes up to 1500 , then sometimes carries on up to 2000 without any throttle input. I assume I need to rebalance the throttle bodies and adjust idle,

has new throttle cable and seems fitted properly. 
 

any advice?

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Hi David

this sounds like an air leak…. Probably!

you mention ‘choke’ - is your car a PI or a Carb model?

steve

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Hi David

No expert but if the idle was ok prior I wouldn't adjust anything yet and first check for air leaks.

Bit of a pain but refit the points does the idle stabilise?

Are all the butterflies shut with no choke and throttle.

Andy

 

Edited by PodOne
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I'd check the butterflies are closing correctly, like you said ignition problems may have masked this issue. The only way I can vary my idle speed is with the air screw at the front of the inlet manifold.

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Yes it sounds like the throttles are not/not all closing correctly

it may be worth using a flow meter to check the airflow of each throttle, and then renovating the throttle linkage with polybushes and new adjuster links if necessary

whereabouts are you Dave?

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Check the choke lever is returning fully on the Metering Unit, then make sure the choke and throttle on the linkage has fully returned and isn't wedged a little open, holding the butterfly's slightly open. 

Did you change the timing after doing the ignition work? It may have helped increase the idle revs. 

Are you saying it varies from 500 to 1500/2000 revs or starts low and steadily rises but is stable not fluctuating? 

Gareth

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Hi Steve 

im in Weymouth.

read the brown book today checked butterfly gaps, they were above spec, so cleaned them and as adjusted the linkage to spec. Corrected the timing to 4 degrees it was at 0 degrees. Seems ok I think. Will go round the block I it later, for first drive of it.

 

it’s definitely running best it has done since buying it.

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I generally start my timing process at 11 degrees BTDC, then fine tune it to prevent pinking at low engine speeds. I don't have,and never have had, a vacuum line connected to the distributor.

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Even 4 degrees btdc is a little conservative Dave, with today’s fuels most cars like 8-11btdc

you also need to be aware that the timing marks can slip….

steve

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