How to rebuild a Rochester Quadrajet 4MV carburetor
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=====Loose Power Piston Retainer Cap===== | =====Loose Power Piston Retainer Cap===== | ||
| − | : | + | According to [http://www.hotrodders.com Hotrodders] forum member '''''TommyK''''': |
| − | : | + | <blockquote>''"It is not uncommon for the retainer to fail to positively secure the PP in its hole in and of itself. The solution is to take a chisel and gently stake the edge of the hole in one or two spots against the retainer." ^''</blockquote> |
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=====Worn Shaft Bushings===== | =====Worn Shaft Bushings===== | ||
| − | : | + | According to [http://www.hotrodders.com Hotrodders] forum member '''''cobalt327''''': |
| − | : | + | <blockquote>''Usually the play will be on the primary shaft. The shaft is teflon coated (that green colored material) but despite this, the shaft wears directly on the aluminum of the throttle plate. There are bushing kits to fix this if it's worn too much.</blockquote> |
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| − | + | <blockquote>How much is too much? If you get an erratic idle or if it's obviously worn out. There will be play in ALL of them, though and that's where determining how much is too much is tricky. But if it idles good, it's good to go, IMO." ^''</blockquote> | |
=====Cleaning Float Bowl Orifices===== | =====Cleaning Float Bowl Orifices===== | ||
Please see posts numbers 23 through 28 on page 2 in the thread ''[http://www.hotrodders.com/forum/rochester-quadrajet-4mv-carburetor-removal-disassembly-rebuild-rookie-level-190558-2.html Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level)]''. | Please see posts numbers 23 through 28 on page 2 in the thread ''[http://www.hotrodders.com/forum/rochester-quadrajet-4mv-carburetor-removal-disassembly-rebuild-rookie-level-190558-2.html Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level)]''. | ||
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| + | =====Throttle Blades===== | ||
| + | According to [http://www.hotrodders.com Hotrodders] forum member '''''cobalt327''''': | ||
| + | <blockquote>''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 w/A/F distribution w/some intakes. While this may be true, until you have a good grasp on the engine's tune and plug readings indicate a need for this, keep them @ 90°." ^''</blockquote> | ||
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''Coming soon.'' | ''Coming soon.'' | ||
| − | Before | + | Before beginning the rebuild, be sure all potential issues listed in the '''''Trouble Spots''''' section have been inspected and addressed. |
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'''Cautionary Note:''' According to [http://www.hotrodders.com Hotrodders] forum member '''''cyclopsblown34''''': | '''Cautionary Note:''' According to [http://www.hotrodders.com Hotrodders] forum member '''''cyclopsblown34''''': | ||
<blockquote>''"That nut on the backside of the carburetor base plate, do not overtighten it. Use a thread sealant tape or paste on it and don't wrench down hard on it, the casting is thin and will crack if over torqued. you can pretty much get it tight by feel, the sealant allows you to tighten it with less torque and still have a good seal." ^''</blockquote> | <blockquote>''"That nut on the backside of the carburetor base plate, do not overtighten it. Use a thread sealant tape or paste on it and don't wrench down hard on it, the casting is thin and will crack if over torqued. you can pretty much get it tight by feel, the sealant allows you to tighten it with less torque and still have a good seal." ^''</blockquote> | ||
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| + | '''Cautionary Note:''' According to [http://www.hotrodders.com Hotrodders] forum member '''''cobalt327''''': | ||
| + | <blockquote>''"...tighten the carb to the thick insulator-type gasket evenly but not too tightly. Because the gasket of that type has a lot of give to it, it can cause the base plate to warp- sometimes enough to cause the throttle shafts/blades to bind." ^''</blockquote> | ||
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''Coming soon.'' | ''Coming soon.'' | ||
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| + | '''Tuning Tip:''' According to [http://www.hotrodders.com Hotrodders] forum member '''''cobalt327''''': | ||
| + | <blockquote>''"The idle discharge ports that are controlled by the idle mixture screws can be anywhere from around 0.050" to 0.080". If you find a lean idle condition that doesn't seem to respond to turning out the screws CCW, you can gauge the port size then enlarge it one size at a time until you regain control w/the screws.''</blockquote> | ||
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| + | <blockquote>''This is providing that the throttle plates are not open too far due to a large cam- which will over-expose the transfer slot, just like on a Holley. The cure for that is the same as you'd do w/a Holley- start by using more ignition advance. This allows the primary throttle blades to be closed down some to lower the idle speed, which increases due to the advanced timing. Often, this is all that's needed, so be sure to do this FIRST, then enlarge the ports only if still needed." ^''</blockquote> | ||
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