Need help with my freshly rebuilt carb

[iservin619]

I have a 84 gmc with a computer controlled carburetor. The original one was giving me issues so I bought a rebuilt one from national carburetors. Didn’t have the time or patience to rebuild the original one. I since installed it onto the truck and did not touch a single screw except for the one that controls idle on the far right of the carburetor near the throttle cable. Drove it around and it runs pretty good but I can hear it backfire at times after flooring it a bit. How do you go about adjusting the carburetor I just bought the flexible carburetor adjuster and I saw a video saying I would need a dwell meter. What do you guys think ? Is there anything else I should check before doing that. It’s also my first time ever fidgeting and working with carburetors so if you have any tips or trick or even videos I should watch I’d appreciate it all the videos I have seen are not computerized carburetors bought a vacuum gauge but turns out that is a not gonna work out. I appreciate all the help.

 

[75 Chevy SWB 4x4]

I've used a vacuum gauge several times to dial in the curb idle mixture circuits on carbs. Is there not a vacuum port on the carb itself?

 

[iservin619]

I've used a vacuum gauge several times to dial in the curb idle mixture circuits on carbs. Is there not a vacuum port on the carb itself?

There is a vacuum port but I saw a YouTube video saying that vacuum gauge doesn't work for computerized carburetors.

 

[iservin619]

I have a 84 gmc with a computer controlled carburetor. The original one was giving me issues so I bought a rebuilt one from national carburetors. Didn’t have the time or patience to rebuild the original one. I since installed it onto the truck and did not touch a single screw except for the one that controls idle on the far right of the carburetor near the throttle cable. Drove it around and it runs pretty good but I can hear it backfire at times after flooring it a bit. How do you go about adjusting the carburetor I just bought the flexible carburetor adjuster and I saw a video saying I would need a dwell meter. What do you guys think ? Is there anything else I should check before doing that. It’s also my first time ever fidgeting and working with carburetors so if you have any tips or trick or even videos I should watch I’d appreciate it all the videos I have seen are not computerized carburetors bought a vacuum gauge but turns out that is a not gonna work out. I appreciate all the help.

Forgot to add but there is also this random wire I have no clue what it goes to do any of you have an idea what it is ??

 

[Ricko1966]

Check all ignition,timing and vacuum leaks first. The adjustments you can make to that carbureator are not likely to cure or cause a back fire. It is probably ignition.

 

[Matt69olds]

It’s been 30 years since I messed with setting the mixture control solenoid on those carbs. If I remember correctly, there is a green connector somewhere near the carb where you put the dwell meter. Basically, you raise the engine rpm to 2500 (I think) and set the metering rod stops so the dwell meter reads 30* degrees (I think!). It’s the same basic process as setting up an Adjustable Part Throttle on a standard Q-Jet.

Watch this :

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And this:

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Some more videos I found:

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Hope that helps.

Setting the dwell puts the metering rods in the middle of their adjustment range so the computer has lots of room to make adjustments to the mixture, depending on load and altitude. Since it’s 40 years out of date, nobody knows how to calibrate them.

Just another example of why ignorant people think Q-Jets are junk. Set them up correctly, they work very well.