[Healeys] Carb Adjustment Epiphany

[Bob Spidell]

I've tried all the techniques: lifting pin, Colortunes and, most 
recently, an exhaust gas analyzer.  My observations:

- never had any luck achieving the elusive 'Bunsen blue' with 
Colortunes--could only get to a lighter shade of orange before the 
engine ran lean rough
- EGA was a disappointment--response is too slow and actually started to 
melt the plastic pickup pipe.  Also, I have an H-pipe in my exhaust so 
it's impossible to isolate the carb mixtures, and I've wrapped the down 
pipes so the exhaust gas is now scorching hot ;)
- lifting pins worked OK, but you have to have mixtures pretty well 
dialed-in to begin with

A carburettor isn't a precision device to begin with--it more-or-less 
just dumps fuel into an airstream (IMO, SUs are superior to 
American-style fixed choke carbs, however).  I think you can do well 
enough--without a dyno and custom needles, at least--by balancing the 
airflow (I use a Unisyn) then adjusting each carb in turn from lean 
rough to rich rough and splitting the difference, erring on the rich 
side.  Then use the lifting pins, and check the plugs.


Bob


Oudesluys wrote:
> I have always used the good old Colortunes to set the mixture of SU's 
> of my Spitfire in the past, fast, easy and rather accurate. CO around 
> 3-5%. Even use them now on twin Dellorto's, they never fail me. Start 
> with the jet orifice level with the carbs surface, if you are starting 
> from scratch.
>
> You have to balance the SU's first. The easiest is starting of with a 
> length of tube to listen to the hiss of each carb at idle and adjust 
> untill that is equal for all carbs, then set the mixture and then you 
> may need very slight fidling the balance screws untill the engine is 
> smoothest in pick up.
> A Morgan Carbtune is of limited or no use with a balance pipe.
>
> Kees Oudesluijs
> NL
>
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Bob Spidell           San Jose, CA            bspidell at comcast.net

"Not everything that can be counted counts, and not everything 
that counts can be counted." -- Albert Einstein
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