[Healeys] slow idle setting

[Bob Spidell]

I'll take a stab.

I've seen two 'definitive' methods for setting idle on HD carbs: one says close the slow run valves and set with 
throttle opening screws, the other (more prevalent) method is the 'close the throttles and open the slow run valves 2.5 
turns then fiddle' method.  I don't like the idea of the throttle plates closing on the throttle bore, so I set the 
throttle screws to just open the plates then set the idle with the slow run valves, checking the balance after every 
adjustment.  I think I usually set the throttle screws so that I have to open the valves about 2 turns--I'm at sea 
level--so I can open them up a little if need be when at altitude (my normal idle down here is 750-800RPM).  If your 
engine doesn't quit when you close the slow run valves either the valves are leaking or the throttle plates are open (or 
you have a terrible vacuum leak somewhere).  My BJ8 idles consistent and smooth (well, consistent anyways).

You don't say why you set the timing advanced, but that could have something to do with it.  Also, you shouldn't get 
black smoke anywhere along the normal power curve; at least, neither my BJ8 or BN2 blow any black smoke (except with 
full-on 'choke').  Check to make sure your  'choke'--SUs don't actually have a choke--activation levers are fully down 
(they're notorious for sticking).

Bob


On 4/9/2014 2:56 PM, Richard Kahn wrote:
> I was trying to adjust and balance my HD8s and I cannot figure out the slow
> idle.   I am at 6500 ft elevation and the idle is at 800 RPM. When I drive at
> lower altitudes the slow idle goes to 1000 to 1200 RPM.  Not a problem as the
> BJ8 runs very well. Yesterday, I tried the "cook book" tuning method. When I
> close the slow idle screws then open them 2 1/2 turns the idle is high and I
> get black smoke. I turned the screws evenly a half turn at a time until the
> RPM went down as low as it would go but the best I could get is 800 RPM. The
> screws are now only 1/2 turn open. Again it runs fine. What is going on? I am
> running the timing a little advanced on purpose. Carbs are balanced and I use
> two Colortunes to set the fuel mixture. I will be doing a lot of lower
> altitude driving this year and was hoping to get this worked out if I can.
> _______________________________________________
>
>
>


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Bob Spidell           San Jose, CA            bspidell at comcast.net

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