SU carbs / idle - 79 mgb

[ate1980]

Hi,

I finally got round to weakening my over rich mixture today, after resolving another points based problem.
- drove car up to temperature (until fan was cutting in and out)
- balanced the air flow
- reduced the mixture, until the revs rise then fall when piston is raised.
- re checked the airflow

This made a huge improvement as the idle became much much smoother. Idle was perfect at 800. Drove the car and it ran really well. Got home and notice the idle is now much higher, 1100-1200. I would just turn the screws in except the right carb is already full adjusted.

Is there a problem with fast idling, why may it have changed after a 10 minute drive ?

thanks as ever

Andrew

[Grease Monkey]

Hi Andrew, don't touch the mixture screws (jets), slacken the connecting rod between the carbs and slacken off the throttle stop screws, twin carbs should always be set up as seperates with the ability to adjust the idle speed/air flow independent of one another. Another point, did you originally set up the carbs with air cleaners off? Replacing them and road testing may have made for a richer mixture.


John Simpson.

[Wicksy]

Agree with above but first check that the throttles are coming back on their stops - had the same problem as you with my older B, you could reduce the idle by pressing firmly on the throtlle levers. Problem was a weak throtle return spring, replaced it and sorted