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I'm rebuilding the carburetor and having a problem with the secondary throttle shaft binding. This has been a problem for a while and since it had been rebuilt in the past I figured I or someone else had screwed up somewhere. Since the shaft binds the vacuum secondary barrels does not work and I basically have a 2bbl carb.
The entire unit was gummed up terribly so I dismantled it completely including the throttle plates and gave everything thing a good soak. After degreasing I dipped all the steel parts in muriatic so all the rust is off. Brass got treated with muriatic to clean off any loose iron rust or aluminum deposits. I soaked the aluminum in dilute boiling vinegar. I then rinsed everything for a long while in hot water, dried, then fine wire brushed polished and cleaned everything.
For those who may be unaware, muriatic will dissolve aluminum in an exothermic reaction, so don't treat aluminum that way. There is a product called Acid Magic that is muriatic acid stabilized in some way so it releases far less noxious gas when treating rusted steel.
I cleaned the shaft bores with a fine wire gun-barrel brush and the shafts with 600 grit sandpaper. A light coat of WD-40 and they turn nicely with no excessive clearance or binding. That is, until I install the plates on the secondary shaft.
Throttle plates are oval, not round, since they seal a round hole at a slight angle. The plate edges are machined at that same angle. Put them in upside-down and they will bind as the sharp corner contacts the soft aluminum barrel; right-side-up and they seal perfectly without binding.
The primary plates have a bevel at the upper surface facing the front of the carb to reduce the plate thickness slightly. This allows more precise interaction with tiny sensing holes in the side of the barrel; three lined up vertically. One of the plates has a tiny factory indent at the front edge that lines up with at least one of the holes and I'm not sure why. Is there a right and left plate? The sensing holes in the right and left barrels appear to be identical. I installed the screws, tightened them down and the shaft turns without binding.
The secondary plates have no thickness bevel but because of the edge bevel they only go in one way. When I put them in and install the screws the shaft turns freely and the plates seal perfectly. However when I tighten the screws the shaft binds. The plates do not appear to be perfectly flat, so when tightened against the weak brass shaft it apparently bends it and hence the binding. I switched the plates right to left and no difference.
What am I doing wrong?
The entire unit was gummed up terribly so I dismantled it completely including the throttle plates and gave everything thing a good soak. After degreasing I dipped all the steel parts in muriatic so all the rust is off. Brass got treated with muriatic to clean off any loose iron rust or aluminum deposits. I soaked the aluminum in dilute boiling vinegar. I then rinsed everything for a long while in hot water, dried, then fine wire brushed polished and cleaned everything.
For those who may be unaware, muriatic will dissolve aluminum in an exothermic reaction, so don't treat aluminum that way. There is a product called Acid Magic that is muriatic acid stabilized in some way so it releases far less noxious gas when treating rusted steel.
I cleaned the shaft bores with a fine wire gun-barrel brush and the shafts with 600 grit sandpaper. A light coat of WD-40 and they turn nicely with no excessive clearance or binding. That is, until I install the plates on the secondary shaft.
Throttle plates are oval, not round, since they seal a round hole at a slight angle. The plate edges are machined at that same angle. Put them in upside-down and they will bind as the sharp corner contacts the soft aluminum barrel; right-side-up and they seal perfectly without binding.
The primary plates have a bevel at the upper surface facing the front of the carb to reduce the plate thickness slightly. This allows more precise interaction with tiny sensing holes in the side of the barrel; three lined up vertically. One of the plates has a tiny factory indent at the front edge that lines up with at least one of the holes and I'm not sure why. Is there a right and left plate? The sensing holes in the right and left barrels appear to be identical. I installed the screws, tightened them down and the shaft turns without binding.
The secondary plates have no thickness bevel but because of the edge bevel they only go in one way. When I put them in and install the screws the shaft turns freely and the plates seal perfectly. However when I tighten the screws the shaft binds. The plates do not appear to be perfectly flat, so when tightened against the weak brass shaft it apparently bends it and hence the binding. I switched the plates right to left and no difference.
What am I doing wrong?
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