How to rebuild a Rochester Quadrajet 4MV carburetor
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=====Leaking float bowl well plugs===== | =====Leaking float bowl well plugs===== | ||
| − | A common problem on the early (1968-back) Q-jets especially, is leaky | + | A common problem (mostly) on the early (1968-back) Q-jets especially, is leaky wells. The early leak-prone plugs can be identified by being brass cup-type plugs as opposed to aluminum. The late-type plugs are shown below, left- front plugs arrows, rear plugs circled. The 'cure' for this has long been to use JB Weld, etc. to seal them over. This is just a stop-gap measure, the epoxy will degrade and quit sealing. |
The well plug stop-leak pads that come in many rebuild kits are a joke (below, center and right). They will seal the leaking rear plugs for a few heat cycles before shrinking down to a fraction of their former thickness. The result is the carb will initially run as it should, ''quickly'' followed by the same symptoms of a leaky plug returning. Do not waste your time with them. If you have a leaking plug, repair it right. | The well plug stop-leak pads that come in many rebuild kits are a joke (below, center and right). They will seal the leaking rear plugs for a few heat cycles before shrinking down to a fraction of their former thickness. The result is the carb will initially run as it should, ''quickly'' followed by the same symptoms of a leaky plug returning. Do not waste your time with them. If you have a leaking plug, repair it right. | ||
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[[File:Q jet well plugs.jpg|400px]][[File:WELL PLUG 1.jpg|295px]][[File:WELL PLUG 2.jpg]] | [[File:Q jet well plugs.jpg|400px]][[File:WELL PLUG 1.jpg|295px]][[File:WELL PLUG 2.jpg]] | ||
| − | FWIW, there is an epoxy by Devcon (made in the USA, look for "Devcon Home"). It comes in the older 2 tube packages and the newer double plunger syringe type. On the back it clearly states it <u>*RESISTS UNLEADED FUEL*</u>, salt, gasoline, oil etc. Full set time 8-12 hrs/2500 psi. However, be aware there is no empirical evidence that this epoxy will work for the life of the carb without any delamination or degradation | + | The tell-tail signs of leaking well plugs is if the carb float bowl empties overnight. This will usually leave a small hit of fuel in the bottom of the accelerator pump well, but unless the engine starts and runs well when cold (or has an electric fuel pump), the engine will often stall after starting, then will take a lot of cranking for the mechanical pump to refill the bowl and the engine to restart. |
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| + | On the post ~1968 Q-jets, the [B]secondary[/B] plugs are spun in then peened, so to speak. The [I]main[/I] plugs are pressed and sealed w/a soft metal around them- and they can and do leak on some carbs, regardless of the year. | ||
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| + | Epoxy is not the way to fix a leaking main well plug- tapping them for a machine screw works much longer- as in forever. Epoxy will eventually delaminate from the metal and the leak will resume.Ruggles mentions using Marine Tex epoxy to seal the threads of replacement well plugs, but he states that using epoxy alone to repair a leaking well plug is akin to "cutting your arm off and putting a Band-Aid on it". | ||
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| + | FWIW, there is an epoxy by Devcon (made in the USA, look for "Devcon Home"). It comes in the older 2 tube packages and the newer double plunger syringe type. On the back it clearly states it <u>*RESISTS UNLEADED FUEL*</u>, salt, gasoline, oil etc. Full set time 8-12 hrs/2500 psi. However, be aware there is no empirical evidence that this epoxy will work for the life of the carb without any delamination or degradation. | ||
So, if a '''''permanent''''' fix is wanted, the wells can be resealed with new plugs that are peened over to hold them in place, or the wells can be drilled and tapped for plugs that will seal them for good. The primary wells seldom leak, the secondary wells on the early (1968-back) carbs do leak much more often than the later carbs. | So, if a '''''permanent''''' fix is wanted, the wells can be resealed with new plugs that are peened over to hold them in place, or the wells can be drilled and tapped for plugs that will seal them for good. The primary wells seldom leak, the secondary wells on the early (1968-back) carbs do leak much more often than the later carbs. | ||
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