How to rebuild automotive carburetors
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==Holley squarebore carb== | ==Holley squarebore carb== | ||
| − | The squarebore 4bbl Holley is a very flexible carb. The design of the model 4150 and 4160 squarebore Holley 4 barrel carburetor has changed very little since its introduction in 1957, | + | [[Image:Holley.jpg|thumb|left|400px|Holley squarebore Model 4160]] |
| + | The squarebore 4bbl Holley is a very flexible carb. The design of the model 4150 and 4160 squarebore Holley 4 barrel carburetor has changed very little since its introduction in 1957. Repair, rebuilding, modifying and tuning techniques remain basically unchanged as well. They are easy to rebuild and tune, and they have great aftermarket support- in fact a "Holley" carb can be assembled without using any Holley parts. | ||
| − | + | It has been many years since a Holley carb (or ANY carb) has been used on a domestic production automobile, but regardless of that, the Holley carb will remain in use for many more years to come- of that there's little doubt. | |
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===Fuel transfer tube=== | ===Fuel transfer tube=== | ||
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===Power valve=== | ===Power valve=== | ||
| − | The Holley carb uses a power valve to supply additional fuel when the engine vacuum drops (and presumably the engine load increases). The amount of fuel it supplies is equal to about 7-8 jet numbers. If the rear power valve (if present) is removed, the threaded hole it was in has to be plugged. The jets have to be enlarged 7-8 jet sizes to compensate for the loss of fuel flow it provided. | + | [[File:Holley pv stamping1 id.jpg|thumb|left|400px| Holley power valve vacuum rating]] |
| − | + | The Holley carb uses a power valve to supply additional fuel when the engine vacuum drops (and presumably the engine load increases). The amount of fuel it supplies is equal to about 7-8 jet numbers. If the rear power valve (if present) is removed, the threaded hole it was in has to be plugged. The jets have to be enlarged 7-8 jet sizes to compensate for the loss of fuel flow it provided. <br style="clear:both"/> | |
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===Transfer slot=== | ===Transfer slot=== | ||
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[[File:Holley transferslot.jpg]] <br style="clear:both"/> | [[File:Holley transferslot.jpg]] <br style="clear:both"/> | ||
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==Rochester Quadrajet carb== | ==Rochester Quadrajet carb== | ||
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[[Image:Rochester.jpg]] <br style="clear:both"/> | [[Image:Rochester.jpg]] <br style="clear:both"/> | ||
| − | + | Because of its ability to be tailored to work with a variety of engines and circumstances, the Rochester Quadrajet- if properly built and tuned- is one of the best carburetors available. With its small primaries, you can get reasonable fuel mileage, or you can kick in those monster secondaries, forget about fuel mileage, and fly. | |
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| + | It does have its limitations, though. For instance, if you are running a cam that causes the vacuum to be low, the Q-jet power piston spring needs to be selected carefully- just as you would do a Holley power valve. Several companies make different power piston springs for such applications, and jets and metering rods are also available. | ||
| − | + | In maximum performance applications, one problem with the Q-jet that's difficult to overcome is the small float bowl. In cases where the engine is large and the RPM high, there's insufficient volume in the Q-jet fuel bowl. This is often countered by using a much higher than normal fuel pressure. This in turn requires the float and inlet valve (needle and seat) assembly to be modified to handle the higher fuel pressure, otherwise the carb will flood due to the fuel pressure overpowering the float/needle valve assembly's ability to shut the flow off when the desired float level is reached. | |
| − | + | Used under the right circumstances, the Quadrajet is a great all around carb for many street machines. Although Holley carbs were seen on a few Chevy engines during the '60s and '70s- most notably on high performance small and big block Chevy engines (including the three 2-barrel 'Vette big block engines)- the Q-jet carb was original equipment on most GM muscle car engines from that era. | |
| − | + | Once tuned, it tends to hold that tune unless dirt gets into the air bleeds or clogs the jets or other orifices. This is usually caused by a bad or missing air filter- so '''always''' use a clean air filter! Don't remove it at the track, either. Often a correctly shaped filter housing base and a free flowing filter will out perform no filter base and filter, so adding performance by removing the filter is a fallacy. | |
| + | It's true that the Q-jet is somewhat more difficult to rebuild than a generic Holley, at least the first time. But after the first one, the process becomes much easier until after a few rebuilds, it becomes second nature. Some types of changes to the tune of the Q-jet requires drilling orifices and/or replacing air bleed and fuel supply tubes; this too will be daunting at first. This is where a book like '''''How to Rebuild and Modify Rochester Quadrajet Carburetors''''' by Cliff Ruggles is a big help. In addition to his book, Cliff Ruggles also maintains a website ([http://www.cliffshighperformance.com/ Cliff's High Performance]), with a forum dedicated to discussing carburetors. Another highly regarded title on the Q-jet carb is '''''Rochester Carburetors"''''' by Doug Roe/Bill Fisher. | ||
| − | + | Most rebuild kits come complete with instructions and application charts for whatever engine your working with, and you can always hold on to the parts you didn't use and use them on your next rebuild or experiment. Several companies make everything you need to tune the Q-jet to fit your needs, or you can buy a new carb from Edelbrock. [http://www.jetchip.com/ Jet Performance] also sells Q-jets in several stages to meet your application. If your running a nice little street engine with a little thump, you can't find a better carb, but if your getting into monster pro street territory, you need to look to carburetors that can handle the needs of these engines and/or have a very good understanding of the tuning requirements needed to allow the Q-jet to work well under these conditions. | |
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| + | ===See also:=== | ||
| + | *[[How to Rebuild a Rochester Quadrajet 4MV Carburetor]] | ||
===Quadrajet Tuning and Repair Parts=== | ===Quadrajet Tuning and Repair Parts=== | ||
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*[http://www.edelbrock.com/ Edelbrock] | *[http://www.edelbrock.com/ Edelbrock] | ||
| − | ==Carter | + | ==Carter carb== |
[[Image:Thermoquad.jpg]] | [[Image:Thermoquad.jpg]] | ||
| − | ==Stromberg | + | ==Stromberg carb== |
[[Image:Stromberg.jpg]] | [[Image:Stromberg.jpg]] | ||
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==Actual rebuild procedure== | ==Actual rebuild procedure== | ||
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