[Spridgets] Rejetting carbs for high altitude

rrengineer @dslextreme.com rrengineer at dslextreme.com
Mon Mar 23 12:48:22 MST 2009


I live in San Bernardino, California which at above seal level by 1157
feet.  I know this from my flight engineer days at Norton Air Force base.
I have been up to Big Bear lake with my Bugeye and have only set my carbs
leaner by a flat or two each time.  The car ran fine as long I remembered to
richen them back up when I got back down from the Mountain.  Big Bear lake
is about 7000 feet above sea level.  Just to add to the confusion, I had to
monitor two altitudes on the C141 aircraft, height above sea level for
engine performance and height above ground level for aircraft longevity.
Mike MacLean
60 Sprite
56 BN2

On Mon, Mar 23, 2009 at 12:33 PM, JLC <breton48 at live.com> wrote:

> Thanks to Roan Soave and WeslakeMonza1330 for replying...
>
> I could not remember if the ignition had to be retarded or advanced for
> high
> altitude... Could you explain to me why it has to be advanced? I am running
> at 25 degrees advanced at idle, 35 at 4000-45000 rpm. I'll try 28 and 38.
>
> I know it's running too rich because I can see the "black soot" from the
> side exhaust on the rear left fender! Did not used to do that... in fact,
> the original setting by the engine rebuilder was on the lean side, and I
> should have left it there. I had the car dynoed in San Diego, and it was
> running somewhat rich after that, even at sea level. According to the dyno
> graph, the air/fuel ratio varied from a low 11 to 1 at 3000 rpm to a high
> 14.4 at 2000 rpm - it was 13.1 at 6297 (max power with 115 hp at rear
> wheels).
>
> I am running NGK BCP 6ES plugs - will try two grades hooter for the same
> plug.
>
> I will buy an airflow meter... I can use it on another car too. Any
> suggestions for a good one at a reasonable price?
>
> Thanks again,
>
> JLC
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