carb tick over

[johngosnell]

AS most of you know I am stuck in a wheelchair so I am only able to see the top of the carbs, a very basic question regarding tick over. My car at the moment tick over is about 500 RPM but when the gearbox is engaged it slows down to about 400 rpm so I want to get the tick over up to about 600-650 rpm so when the gearbox is engaged she is at 500 rpm. So is there a single throttle stop that can be adjusted or is it individual via the slow run valve.


john
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[cass3958]

You could do it either way John, but the correct way is to adjust the slow running jet on both carbs individually, raising the tickover with one carb and then balancing the second carb with the first. Any other adjustment trying to do both at the same time would involve adjusting the throttle stops which operate the butterflies but this is not the correct way.
For you this would be a difficult job as the slow running jet screws are on top of the carbs but placed down the sides and you need a long shafted flat bladed screwdriver to come in from the top. When I have done it I have basically had to lie across the top of the wing to be able to look down through a small gap between the carb and the air filter housing tube to locate the adjustment screw. Especially the rear one where the bonnet gets in the way and you end up with your nose about two inches from the top of the carb with the back of your head hitting the underside of the bonnet.

I think from memory with the tick over for a manual car should be about 500 RPM but slightly higher for an automatic at 600 RPM when in park or neutral.

Attached is a photo from the service manual showing where the mixture and slow running screws are located.

[johngosnell]

Thanks for the detail on adjustments, personally before being in a chair I had only dealt with single carb cars so it was just adjust the throttle stop to the correct speed


Best wishes john


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[Glyn Ruck]

John ~ as I learn the vagaries of SU carbs ~ for repeatable & stable idle speed (important with an Auto) the only way is the slow running volume screws. Forget about the throttle stop/s.

[Orlando St.R]

It's also worth saying, in case it's not obvious, that if the car is running sweetly and in balance at 500rpm, you just need to unscrew (anti-clockwise) each slow-running screw by the same amount, probably a quarter turn at a time, until you have reached the desired speed. Of course, to do that, you have to do the wing-sprawling thing Rob describes to see the screws. I think you will need an assistant for this.

It's an idea to put a dab of paint on one side of the screw and then photograph the starting points. That way you can return to where you started if need be.

I agree with Rob 600 - 700rpm is probably ideal for the DG auto. Too little and it chunters when you select a gear; too much and it thumps into gear when you select one. When you get neither symptom, you have reached the perfect idle speed for your car.

Also, make sure the car is well up to temperature when you make the adjustments.

[johngosnell]

I'm at a car show on Sunday so hopefully I will get somebody to do it for me after that. Thanks again for all the relevant info, What has been said is what I had thought but never getting it adjusted before I was not sure.


Regards John



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