How to rebuild a Rochester Quadrajet 4MV carburetor
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Also please see post #48 on [http://www.hotrodders.com/forum/rochester-quadrajet-4mv-carburetor-removal-disassembly-rebuild-rookie-level-190558-4.html page 4] on the thread [http://www.hotrodders.com/forum/rochester-quadrajet-4mv-carburetor-removal-disassembly-rebuild-rookie-level-190558.html ''"Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level")''] | Also please see post #48 on [http://www.hotrodders.com/forum/rochester-quadrajet-4mv-carburetor-removal-disassembly-rebuild-rookie-level-190558-4.html page 4] on the thread [http://www.hotrodders.com/forum/rochester-quadrajet-4mv-carburetor-removal-disassembly-rebuild-rookie-level-190558.html ''"Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level")''] | ||
| − | [[File:Quadrajet- Detriorated Epoxy on Wells.jpg|thumb|center|450px| | + | [[File:Quadrajet- Detriorated Epoxy on Wells.jpg|thumb|center|450px|Deteriorated epoxy on a Quadrajet 4MV]]Please see Post #76-78 and #90 on [http://www.hotrodders.com/forum/1977-chevy-k20-engine-suffers-hesitation-power-loss-when-drive-213757-6.html page 6] of the thread [http://www.hotrodders.com/forum/1977-chevy-k20-engine-suffers-hesitation-power-loss-when-drive-213757-6.html ''"1977 Chevy K20: Engine Suffers from Hesitation/Power Loss When In Drive"''] |
=====Worn Shaft Bushings===== | =====Worn Shaft Bushings===== | ||
| − | + | 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 this if it's worn too much. | |
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| − | + | How much wear is too much? If you get an erratic idle or if the shaft moves fore and aft a considerable amount it's obviously worn out. This 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). 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. But if it idles good, it's good to go. | |
According to Hotrodders forum member '''''willys36@aol.com''''': | According to Hotrodders forum member '''''willys36@aol.com''''': | ||
<blockquote>''Worn throttle shafts are self-inflicted. To avoid premature wear on any carburetor, set up the throttle return spring as shown in the 'Best Case' in this picture: [http://www.hotrodders.com/gallery/data/500/2439throttle.jpg Click here for image].''</blockquote> | <blockquote>''Worn throttle shafts are self-inflicted. To avoid premature wear on any carburetor, set up the throttle return spring as shown in the 'Best Case' in this picture: [http://www.hotrodders.com/gallery/data/500/2439throttle.jpg Click here for image].''</blockquote> | ||
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| + | =====Throttle blade screw removal===== | ||
| + | If primary throttle shaft bushings are to be installed, the throttle shaft has to first be removed. After removing all the linkages and choke parts from the end of the shaft, the throttle blades will need to be removed. | ||
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| + | First, the ends of the original screws have to be ground away because they're "staked" at the factory. You may notice the ends are split a slight amount to make them impossible to loosen, back out and fall into the intake. | ||
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| + | [[File:STAKED QJET SCREW.jpg|border|250px|left]] | ||
| + | Should a screw get broken off in the shaft, it can be removed by whatever method available; often drilling is done but be careful to get centered on the broken screw. A drill press is the way to do this best, with the throttle plate clamped down. There's no need to worry about matching the screw sizes side-to-side, in other words, if only one screw broke off, use the other original threaded hole along with the larger hole made for the broken screw. Just use the next larger size and use loctite as well as "peening" the ends of the screws. | ||
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| + | To do the peening, you can clamp a piece of square stock into a vice to use as an anvil to support the screw head on, then peen the ends of the screws with a small jeweler's hammer or ball peen. You don't need to simulate the factory way of staking; the main idea is to disrupt the threads on the end of the screw so they cannot fall into the engine. The loctite will do the rest. | ||
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| + | If the ends of the screws look too long, they can be ground down w/a dremel to the approximate length of the stock screws before peening them. | ||
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| + | Be very careful if you end up trying to find a replacement for the secondary shaft. They are not all the same. I'm curious. Why did you remove the shaft if you aren't bushing it? | ||
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| + | The secondary throttle shaft do not need bushings. If the secondary shaft/throttle plate bore is that bad, the rest of the carb is likely worn badly; another core or at a least another throttle plate should be considered. | ||
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=====Throttle Blades===== | =====Throttle Blades===== | ||
| − | + | Check the base plate to be sure the throttle blades are exactly 90° when wide open. There are some who believe having the secondary throttle blades go "over center" helps with A/F distribution in some cases using certain intake manifolds. While this may be true, until you have a good grasp on the engine tune, and unless the plug readings indicate a need for this, keep them at 90°. | |
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| + | The linkage adjustment is fairly easy to do, it only takes a pair of pliers and a bit of patience to get then set perfectly. | ||
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