How to rebuild a Rochester Quadrajet 4MV carburetor
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m (→Throttle shaft bore wear: Minor text addition) |
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The primary bore of the aluminum throttle plate is where the majority of wear is going to be. The shaft has an anti friction coating (the green colored material seen on the shaft and some linkages) but even so, the shaft wears directly on the aluminum of the throttle plate, so the primary shaft will also show some wear- but being steel on aluminum, the shaft wear is going to be much less than seen in the bore. There are bushing kits to fix the throttle shaft bores that use a brass oilite-type bushing if the bore is worn too much. | The primary bore of the aluminum throttle plate is where the majority of wear is going to be. The shaft has an anti friction coating (the green colored material seen on the shaft and some linkages) but even so, the shaft wears directly on the aluminum of the throttle plate, so the primary shaft will also show some wear- but being steel on aluminum, the shaft wear is going to be much less than seen in the bore. There are bushing kits to fix the throttle shaft bores that use a brass oilite-type bushing if the bore is worn too much. | ||
| − | How much wear is too much? There will be some play in ALL Q-jets (even new ones); that's why determining how much is ''too'' much is a little tricky. | + | How much wear is too much? There will be some play in ALL Q-jets (even new ones); that's why determining how much is ''too'' much is a little tricky. Basically if it idles good and the idle is steady even when the throttle shaft is moved fore and aft, it's good to go. But if you get an erratic or unsteady "hunting" idle, or if the shaft moves fore and aft a considerable amount- especially if there's enough wear that the throttle blade can contact the throttle bore- the throttle shaft bore is obviously worn out and needs bushed or the entire throttle plate can be replaced. Wear on the throttle shaft bore is mainly caused by the tension the throttle return spring exerts on the shaft/bore, especially if the return spring is installed wrong (more on this below). |
Wear on the primary shaft bores of the throttle plate can be avoided by properly orientating the return spring. While theoretically the best way is to use a bellcrank ("Best", below), using a throttle return spring in front of, and in line with, the throttle cable or linkage ("Better", below) is simpler and very nearly as good as a bellcrank assembly: | Wear on the primary shaft bores of the throttle plate can be avoided by properly orientating the return spring. While theoretically the best way is to use a bellcrank ("Best", below), using a throttle return spring in front of, and in line with, the throttle cable or linkage ("Better", below) is simpler and very nearly as good as a bellcrank assembly: | ||
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