In the case of the Holley carb, I found an adjustable jet made by Percy's called
the Adjust-a-jet that allows you to adjust the mixture with a screwdriver. It
is in the JC Whitney catalog. About $85. Looks interesting. Fits the 4160,
dont know if it fits the 4165 I have.
Their website is:
http://www.percyshp.com/whatnew.htm
More interesting stuff for us folks planning to get a change in altitude and who
love gadgets.
Ron and Julie
> Richard,
>
> > ... it's hard for me to understand that timing alone is
> > enough in the
> > GMC to compensate for high altitude driving. Do owners of GMC's
> > that are based
> > up above 5,000' or so just adjust timing to compensate for altitude?
>
> Nope, we have to get the fuel mixture right, too.
>
> If your coach is running the ideal air/fuel mixture at low elevation it will
> run rich at altitude. The easiest way to "get by" for a brief trip at
> altitude is to advance the timing a couple of degrees and (if you're fowling
> spark plugs, etc) lean out the mixture a little with the adjustment screws.
> Just remember to put both timing and mixture back upon returning to lower
> elevation.
>
> Emery's setup is really ideal for changing elevations.
>
> Richard ('77 Birchaven)
> rguthart
>
> > Richard Waters
> > '76 PB, Troy, MI
> >
> >
> > > Larry-
> > >
> > > At altitude, it takes a little longer for the flame to spread
> > throughout the
> > > air/fuel mixture because the air is less dense. Consequently you have to
> > > trigger the spark a few degrees earlier in order to create peak
> > pressure in
> > > the combustion chamber at the optimal time. Spec. plus 2-3
> > degrees is what I
> > > run on my vehicles at 5000-6000 ft above sea level. It makes a
> > difference of
> > > several % in fuel economy (and, presumably, horsepower.)
> > >
> > > Richard ('77 Birchaven)
> > > rguthart
the Adjust-a-jet that allows you to adjust the mixture with a screwdriver. It
is in the JC Whitney catalog. About $85. Looks interesting. Fits the 4160,
dont know if it fits the 4165 I have.
Their website is:
http://www.percyshp.com/whatnew.htm
More interesting stuff for us folks planning to get a change in altitude and who
love gadgets.
Ron and Julie
> Richard,
>
> > ... it's hard for me to understand that timing alone is
> > enough in the
> > GMC to compensate for high altitude driving. Do owners of GMC's
> > that are based
> > up above 5,000' or so just adjust timing to compensate for altitude?
>
> Nope, we have to get the fuel mixture right, too.
>
> If your coach is running the ideal air/fuel mixture at low elevation it will
> run rich at altitude. The easiest way to "get by" for a brief trip at
> altitude is to advance the timing a couple of degrees and (if you're fowling
> spark plugs, etc) lean out the mixture a little with the adjustment screws.
> Just remember to put both timing and mixture back upon returning to lower
> elevation.
>
> Emery's setup is really ideal for changing elevations.
>
> Richard ('77 Birchaven)
> rguthart
>
> > Richard Waters
> > '76 PB, Troy, MI
> >
> >
> > > Larry-
> > >
> > > At altitude, it takes a little longer for the flame to spread
> > throughout the
> > > air/fuel mixture because the air is less dense. Consequently you have to
> > > trigger the spark a few degrees earlier in order to create peak
> > pressure in
> > > the combustion chamber at the optimal time. Spec. plus 2-3
> > degrees is what I
> > > run on my vehicles at 5000-6000 ft above sea level. It makes a
> > difference of
> > > several % in fuel economy (and, presumably, horsepower.)
> > >
> > > Richard ('77 Birchaven)
> > > rguthart
