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Carburetor Questions

nad

nad

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I just got my carbureted 350 put into my Blazer and I'm having problems with the carb. It's just a Quadrajet. I'm looking at just buying a new one, maybe a Holley or Edelbrock. I need to know whether I should get a 2 barrel or 4 barrel and what CFM I should go for. I'm new to carbs, so excuse my dumb questions. Any help would be appreciated. Thanks.
 
Was that the carb that was on the engine before? Its likely that carb just needs a rebuild (and cleaned out REALLY well). Q-jets are very sensitive to any kind of dirt.

You could go with another carb, but you will have to tune it. The Q-jet is a very good carb and, IMO, I would stick with what you have :thumb:
 
I would also stick with the Q-jet. You can get pretty good mileage out of them and they run better on hills. If you do decide to get a different carb though, get a 4 barrel.
 
Is there only one type of Q-Jet? Because I was going to go to a junkyard and buy another one to rebuild so that I can still drive my truck, instead of taking the carb off of it and having my truck be down for a day or two.
 
All are of the same basic origins, but there was one major casting change ("emissions" vs. "non-emissions" variants some people call them) and thhen you've got all the choke variations between the different GM divisions, and the different fuel inlet...IIRC, Chev is the only one that used the fuel inlet off to the side.
 
So if I put any other carb on my truck other than the one that is on it right now, I'll have to adjust it and tune it? My truck runs like crap right now, it's really laggy and hesitant.
 
nad said:
So if I put any other carb on my truck other than the one that is on it right now, I'll have to adjust it and tune it? My truck runs like crap right now, it's really laggy and hesitant.
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I would just rebuild the one you have now. It shouldn't take you more than a couple hours.
 
Where can I get a rebuild kit? I've heard that once you rebuild a carburetor, that they never work right again. What's the trick? I can't just buy a Holley Truck Avenger and bolt it right on?
 
nad said:
Where can I get a rebuild kit? I've heard that once you rebuild a carburetor, that they never work right again. What's the trick? I can't just buy a Holley Truck Avenger and bolt it right on?
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That's a load of crap. 95% or rebuilding a carburetor is just cleaning it out. Rebuild kits come with some new parts, but most of it is preventative maintanence stuff, IMO.

There is no carb that you can just bolt on and expect to work right. There are lots of people that will tell you that they have done it (and that's what the companies selling them want you to think). The real deal is that no two engines have identical fuel requirements based on heads, cam, emissions equipment, etc. Not to mention altitude, temperature, humidity, etc.
 
So rebuild it and just make sure that all the adjustments stay the same?
 
hell if you lived a little bit closer i'd have one to give you. ran great on my 305 (did away with it). course you'd have to adjust it and stuff
 
Well adjusting it doesn't seem all that complicated, just a few adjustment screws, right? Actually I had a TBI system in it, but I just got a '79 350 carb motor put in. TBI motors are hard to find around here, and very expensive.
 
nad said:
Well adjusting it doesn't seem all that complicated, just a few adjustment screws, right? Actually I had a TBI system in it, but I just got a '79 350 carb motor put in. TBI motors are hard to find around here, and very expensive.
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If the carb is from a '79, the idle ciruit will be adjusted by the two screws on the front and the primary and secondary circuits are adjusted by changing meter rods and jets.

I would try just rebuilding it before I messed with any of the tuning stuff, especially if the setup used to run well.
 
I don't know if it did or not, my buddy sold it to me and warned me that it had carb problems already. I figured I would just buy a brand new one or rebuilt one and be fine. Any idea what the model number of this one is? Or where I can find it? I have a Haynes manual that tells me how to rebuild it, but I dunno which one I have exactly.

Thanks for all your help. I appreciate it.
 
nad said:
I don't know if it did or not, my buddy sold it to me and warned me that it had carb problems already. I figured I would just buy a brand new one or rebuilt one and be fine. Any idea what the model number of this one is? Or where I can find it? I have a Haynes manual that tells me how to rebuild it, but I dunno which one I have exactly.

Thanks for all your help. I appreciate it.
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The number should be cast on the main body of the carb. Most q-jets are very similar in what is necessary to rebuild them, the # is mostly useful to assure you get the right rebuild kit. There will be rebuild instructions with the rebuild kit too. Taking pictures as you disassemble the carb can help a lot with reassembling it :thumb:
 
Seems like a lot of work. I've rebuilt simple carbs from 4-wheelers and stuff, but just looking at this one gives me a headache.
 
Is there any trick to "tuning" a carb? Just start the truck up and adjust the idle screws and stuff until it runs right? I'm somewhat familiar with import tuning and A/F ratios and whatnot, but I would have no clue how to go about doing it on an old truck. I still think it sounds like it would be easier to buy a new carb and just tune it. They have professionally rebuilt and cleaned Q-Jets on ebay for a good price.
 
There are a few ways to tune the idle. Some use a vacuum gauge (adjust the screws to get the most vacuum at idle). Some go by sound, some adjust the screws and if the idle raises they are adjusting in the right direction, etc.

As for tuning the carb, you can do this for the most part by looking at the porcelain part of the spark plugs. Brown/black plugs indicate a rich mixture, white indicates a lean mixture. You are looking for a light tan color. You adjust the mixture by changing primary metering rods and jets.

Flat spots can fixed by changing the spring on the power piston and/or messing with the accelerator pump.
 
I rebuilt my q-jet on my 85 k5. I never touched a carb in my lift before this one. I never saw one apart before either. Mind you, I did this all on my own, before I found ck5 and with no help from anyone. It's nothing to be scared of in my opinion. All you have to do is PAY ATTENTION to how things come apart. When I say pat attention pay CLOSE attention and you will be fine. Take the carb with you to the auto parts store so they can get the numbers off of it to get you the right rebuild kit. Then take it apart and put it back the same way. Easy as pie. If you want a book to help, there is a haynes manual dedicated to these carbs. I read it after I rebuilt mine. Theres a lot of good info there on how a carb works and what to do with it.

Like I said, I rebuilt mine all on my own, paying very close attention to how it came apart and put it back the same way. My carb runs like a top now. I've had zero issues with it. Good luck.
 
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