Author Topic: 1974 GMC C2500 Runs rough and stalls at red lake gets and in parking lots.  (Read 5263 times)

Offline Henry

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Hi AJ:
Was that gas that was pooled on the intake only at that one spot you photographed? Has it done this before? Is there evidence on where it came from on the side of the carb? Just plugging a vac line should not have caused this. Typically this pooling occurs when the choke plate (top casting of carb) is leaking at the gasket interface with the float bowl (center casting of carb).

If you took if for a test drive and had to feather the throttle to keep it from dying that is an indication that the accelerator pump is not working: the acc pump sends an extra shot of fuel under higher engine demand to keep the air/fuel mixture correct...when the shot doesnt happen when the throttle opens the engine leans out and wants to die until you release the throttle. This symptom sounds different from the symptom you described earlier. I think the inside of your carb is gunked up and causing the float and power valves to stick. It also sounds like the seal on your acc pump is leaking or going out slowly.

When was the last time you rebuilt the carb? Another thing that happens on Q-jets when they get real old is the welch plugs on the bottom of the carb start to leak and this gives all kinds of hard to diagnose drivability problems: occasional stalling, rough running, and refusal to start all after the engine is warm and been running fine for a while. It will run fine when cold and initially when warm. When this is a problem you can look down the throttle bores and see a puddle of gas on the floor of the intake manifold after the engine has stalled.
Regards,
Henry

Offline Smithaj1981

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I just bought the truck 3 months ago so I don't know when the carb was last rebuilt. I've never rebuilt a carb before but it seems like the next step.


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Offline Henry

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Hi AJ:
Rebuilding a Q-jet is a medium size job for an experienced shade tree mechanic and a BIG job and learning experience for a shade tree mechanic who has not done it before. If you have the will, the tools, the shop space, and time you can do it yourself. If not, you will have to find a old school mechanic who can do it. There are also companies on the internet who will sell you a rebuilt one in exchange for yours. If you think you can do it yourself, there will be some downtime on your truck....maybe a week to get it all done and re-installed on your truck. An experienced Q-jet professional mechanic can do it in a day or two. Buying a rebuilt is fastest way but also the most expensive. Either way you go there are plenty of people on this forum to help out and answer questions.
Regards,
Henry

Offline Smithaj1981

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Hi AJ:
Rebuilding a Q-jet is a medium size job for an experienced shade tree mechanic and a BIG job and learning experience for a shade tree mechanic who has not done it before. If you have the will, the tools, the shop space, and time you can do it yourself. If not, you will have to find a old school mechanic who can do it. There are also companies on the internet who will sell you a rebuilt one in exchange for yours. If you think you can do it yourself, there will be some downtime on your truck....maybe a week to get it all done and re-installed on your truck. An experienced Q-jet professional mechanic can do it in a day or two. Buying a rebuilt is fastest way but also the most expensive. Either way you go there are plenty of people on this forum to help out and answer questions.
Regards,
Henry

Thanks. I found a carb from guaranteed carburetors for $178. I think that's my best bet.



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Offline blazer74

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Check the warranty!!!!

Make sure it can be returned/exchanged if u have any issues.
Remanufactured can be hit or miss.

What have others used and experiences on this site.


Offline blazer74

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I would also recommend that if the carb u have is original I would keep it.

Offline Smithaj1981

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Thanks everyone for your help. I rebuilt the carb and it runs like a champ now. Now on the these gas gauges!


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