B ASES DE LA ESTRATEGIA DE DESARROLLO SOSTENIBLE DE LA ZONA

The following tuning points are available for Holley automatic chokes:

a) Adjusting how much the choke plate pulls open when the engine first fires.

As a starting point, the factory tuning settings can be used. The integral chokes which are bolted onto 350 Holley carburettors are normally of two types – either with an adjusting screw, or without one.

If the adjustment screw is present on the side of the choke housing, the following can be used as a starting point:

 Dig the caulking out of the adjustment screw with a sharp pick.

 Remove the choke cap and push the choke pull-off piston inwards (onto the adjustment screw shoulder).

 Apply light closing pressure to the choke plate, then use drill bits to measure the gap between the top edge of the choke plate and the air horn wall (put the drill bit in parallel to and adjacent to the air horn vent, but up against the carburettor wall).  Adjust the screw in or out to give a gap of

approximately ¼”. Turning the adjuster screw counter-clockwise (out) will open the gap, turning the adjuster screw clockwise (in) will close the gap. Note that the adjustment screw should be sealed over again once tuning is finished to prevent vacuum leaks.

If the adjustment screw is not present on the side of the choke housing, the following can be used as a starting point:

 Bend a paper clip so that it has an 1/8” end.

 Remove the choke cap and insert the paper clip into the end of the choke pull-off piston. Feeling gently, hook the paper clip into the piston bore slot.  Move the piston in until the

edge of the piston slot engages the paper clip. The piston is now “pinned” into the bore by the paper clip.

 Apply light closing pressure to

the choke plate, then use drill bits to measure the gap between the top edge of the choke plate and the air horn wall (put the drill bit in parallel to and adjacent to the air horn vent, but up against the carburettor wall).

 Bend the piston lever tang to give a gap of approximately ¼”.

Once this basic setting has been made (and the choke cap reassembled), start the vehicle and observe how the vehicle performs for the first thirty to sixty seconds:

 If the choke plate refuses to move at all when the engine first fires, there may be a number of reasons:

o the cork seal is installed in between the main body and housing may be missing, o the hot air supply may be blocked with carbon, or a lead ball,

o the linkages or the piston could be binding, or

o the vehicle may have a very, very lumpy cam and make insufficient vacuum to move the pull-off piston.

 If the engine is running overly rich (black smoke, strong smell of unburnt fuel, or rich-stalls), adjust the choke pull-off to open the choke plate a tiny bit more.

 If the engine hesitates, backfires or lean-stalls, adjust the choke pull-off to close the choke blade a tiny bit more

Be careful, as a tiny change in the choke pull-off is amplified by the linkage and makes a big difference to the choke plate position.

b) Adjusting how long it takes the choke to start opening once the engine has fired.

The choke plate should be tightly shut when the engine is cold. With either of the hot-air or electric chokes, start the choke coil adjustment by turning the mark on the choke coil to the index position on the housing. To adjust the choke coil, start the vehicle and let it run for thirty to sixty seconds.

 If the engine hesitates, backfires or stalls after the thirty to sixty seconds, the choke is probably opening too soon. Loosen the

three lock screws (see red arrows in the image above) and turn the choke cap one index mark anticlockwise (RICHER). Tighten the three lock screws, let the engine cool all the way down then repeat the tuning.

 If the engine is running very rich (black smoke or the smell of unburnt fuel) after the thirty to sixty seconds, the choke is probably opening too late. Loosen the three lock screws and turn the choke cap one index mark clockwise (LEANER). Tighten the three lock screws, let the engine cool all the way down then repeat the tuning.

 If the choke plate won’t open all the way even long after the engine has warmed up, the problem issue is almost certainly a lack of heat to the choke coil - blocked exhaust crossovers, missing or defective heat riser valves, blown electrical fuses or blown electric coil.

c) Adjusting the unloader tang.

When the engine is cold and the choke is closed, check that the fast idle cam is on the highest step. Push the accelerator slowly to the floor. The choke plate should be observed to be mechanically forced open at least as much as the choke pull-off would open it (about 11/32”). Although not critical, the amount that the choke is

forced open can be adjusted by bending the unloader tang. The tang is pretty heavy, and buried under all the fast-idle linkages – it is easier to remove the choke housing first before bending the unloader tang. The image to the right shows the fast idle screw

(item 1) and the unloading tang (item 2). Bending the unloader tang in the direction of the green arrow will crack open the choke plate more.

11.4 Power Valve Blowout Preventer (Check Ball).