Idle probs

[Slaydog]

Firstly, thx for everybody’s input on this forum, I’m no mechanic but have saved lots of money thanks to the support and advice on here. I recently had an issue with no idle but after trying lots of things it finally came down to a gunged up Idle cut off valve. Problem now is fast idle. It always had a fast idle from cold previously but that stopped after blipping the throttle. What i’d love to know is how should everything behave mechanically after start up? Choke / Carb / Cam Step etc? Does anyone have any resources they could point me to read up and learn? I can’t really debug the issue without knowing how it should work first. One simple thing I’m considering is changing the throttle cable because the coating is sheared in places where it has rubbed against rusty holes that it runs through. Just wondering if it’s getting stuck because I pumped hard and fast on the pedal after starting the other day and it revved really high and stayed there. After that I think I should brave a carb rebuild via brickwerks and the great instruction from @jamesakers videos on his Sir Adventure blog.

[kevtherev]

The choke is operated by a bi-metalic spring.
As this spring heats up from the engine coolant and electric heater, it unwinds and a shaft it is attached to opens the choke. (Takes a 6-8 mins from fully shut)
To facilitate an easy cold start the shaft includes a fast idle mechanism.
This and the choke sets automatically with the depression of the accelerator pedal before starting.

As the ambient temperature increases the mechanism adjusts and will no longer run the engine at a noticeably fast idle, and the choke will be fully off much sooner.

[kevtherev]

The cable should be free to move with no resistance.
If the accelerator cable is sticking or not free, and with further investigation it is found that the pedal mechanism moves freely but the cable is not, then it should be renewed, not oiled or re routed, but renewed.

The carburettor cable linkage has a strong return spring.
Check that it is returning the cable shaft to its home position by removing the cable and turning the shaft by hand

What you are doing here is determining the faulty part.

[kevtherev]

The fast idle mechanism and the choke are adjustable.
If the carburettor has been separated from the autochoke and not returned to the same position then it will need to be reajusted.
The Autochoke housing has three screws.
Once undone the choke duration can be increased or decreased. (Clockwise decreases choke time)
As the mechanisms are interlinked this ajustment will affect the fast idle cam, in so far as reducing the fast idle rpm.

Remember, all this is ambient temperature dependent.
I wpuld suggest its best adjusted in the colder months

If the choke is fully off from fully closed within 8 mins then it's correctly set

[kevtherev]

You must have missed this when searching our site..

viewtopic.php?f=37&t=169025

http://wiki.club8090.co.uk/index.php/Pe ... burg_Choke

[Slaydog]

This is awesome. Thanks @kevtherev for taking time out to explain - it’s helped joins lot of dots. Will sort the cable out first of all as it’s defo sticky.


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