How to adjust q-jet carb the right way

[77jimmy]

It's a 77 jimmy with 350 manual transmission. Edelbrock intake with a q-jet carb. What's a good starting point to start adjusting it. Right now I have to have the ideal screw damn near all the way in. I tryed putting both mixture screws 3 turns out and back the ideal screw out but it won't ideal. Any info would help. I know the edelbrock intake and q- jet is not a good combo. So I just need to get it running better tell I get the money for a better setup.

 

[HotRodPC]

Normally in this case, where the screws are all the way in, or almost all the way and it idles, or have to do so to get it to idle, then you have a bad vacuum leak somewhere. That would be the first thing I looked for. Can of quick start, WD-40 or Carb cleaner and spray around the carb base, intake base and the front and rear of the intake.
If that's all good, then I'd consider an internal leak somewhere. Like, are you sure you have the right intake for that Q jet? It's not a square bore intake is it? Most Qjets won't work on Square bore without an adapter and/or you could be using the wrong carb base gasket.

 

[77jimmy]

There not all the way in there three turns out.

 

[towman]

with a tach turn them out until you get the highest idle, or with a vacuum gauge until you get the highest vacuum reading , if using vacuum gauge get your reading from the manifold

 

[lusktommy]

It's a 77 jimmy with 350 manual transmission. Edelbrock intake with a q-jet carb. What's a good starting point to start adjusting it. Right now I have to have the ideal screw damn near all the way in. I tryed putting both mixture screws 3 turns out and back the ideal screw out but it won't ideal. Any info would help. I know the edelbrock intake and q- jet is not a good combo. So I just need to get it running better tell I get the money for a better setup.

when you say it wont idle and you have the idle screw damn near all the way in you mean it dies or are you having a high idle and it wont come down. you should hear a major vacuum leak, but you wont really hear an intake leak. but the wd40 or carb cleaner hodrodPC mentioned would be what i would try first someone obviously didnt know what they were doing in the first place or they wouldnt of put a rochester on a edelbrock intake. prolly gonna be a loose intake bolt or they torqued the bolts in the wrong order. possible carb bolts or gasket

 

[Jims86]

when you say it wont idle and you have the idle screw damn near all the way in you mean it dies or are you having a high idle and it wont come down. you should hear a major vacuum leak, but you wont really hear an intake leak. but the wd40 or carb cleaner hodrodPC mentioned would be what i would try first someone obviously didnt know what they were doing in the first place or they wouldnt of put a rochester on a edelbrock intake. prolly gonna be a loose intake bolt or they torqued the bolts in the wrong order. possible carb bolts or gasket

What do you mean by the Rochester on Edelbrock intake comment?
Sounds like Conjecture to me.
As far as a base settings to start with, 2-1/4 turns on the idle mixture screws, and maybe 4-1/2 turns on the throttle plates from fully closed.
Nothing wrong with a qjet on an Eddy intake.

 

[crazy4offroad]

Edelbrock makes spread bore intakes, as well as square bore so it is possible they have the right one but it is also possible they have the wrong one lol. If it really is a q-jet on a square bore intake they make adapters to fix that. The extra inch in height you gain from the adapter may add a little performance from it too.

 

[Jims86]

Edelbrock makes spread bore intakes, as well as square bore so it is possible they have the right one but it is also possible they have the wrong one lol. If it really is a q-jet on a square bore intake they make adapters to fix that. The extra inch in height you gain from the adapter may add a little performance from it too.

I hope they put a spreadbore on....I have had some experiences with the square bores and adaptors...had to re jet and re adjust some carbes because the sudden open area under the adaptor plate causes bad JuJu, and falls flat at around 3500rpm.
Despite the adjustments, never really cured the problems...had to get the spread bore intake.

 

[HotRodPC]

Edelbrock makes spread bore intakes, as well as square bore so it is possible they have the right one but it is also possible they have the wrong one lol. If it really is a q-jet on a square bore intake they make adapters to fix that. The extra inch in height you gain from the adapter may add a little performance from it too.

I wouldn't play much into the performance gain, but it's sure possible under the right circumstances, but yes, you can have the wrong Eddy intake for a Q Jet Carb. Spreadbore you're good to go, Squarebore, need adapter. (Or am I backwards?)

 

[Jims86]

I wouldn't play much into the performance gain, but it's sure possible under the right circumstances, but yes, you can have the wrong Eddy intake for a Q Jet Carb. Spreadbore you're good to go, Squarebore, need adapter. (Or am I backwards?)

Nah, you have it right.
Eddy is a good upgrade from stock, and KINDA takes care of the fuel distribution issues.
Stock GM intakes have kind of a "T" that goes frome the carb perch to 1-2, 7-8, where the Eddy kinda "Y's", or is split from the get go, depending on which manifold you get.
As far as Seat of the Pants increases...none really noticeable, but would be in conjunction with other airflow enhancements.

 

[Stroked]

I've never had much luck with the adapter/spacers. Carbs don't seem to like them.

I will agree that there's nothing wrong with a quadrajet on an Edelbrock intake, if you have the correct intake. I ran that for a while on my Camaro, but switched to an Edelbrock carb cause the throttle shafts were worn on my quadrajet.

 

[crazy4offroad]

Back up a minute, someone correct me if I'm wrong here but I don't think a spreadbore carb will even bolt to a squarebore intake. Spreadbore bolt pattern is longer front to back I think. The rear bolts may be a little wider too.

Also, back on the original topic/title of the thread, are there any step-by-step write-ups of how to tune a q-jet? This is something I would like to know how to do since dad's truck has one and it don't seem to run exactly right.

 

[oneluckypops]

Back up a minute, someone correct me if I'm wrong here but I don't think a spreadbore carb will even bolt to a squarebore intake. Spreadbore bolt pattern is longer front to back I think. The rear bolts may be a little wider too.

Also, back on the original topic/title of the thread, are there any step-by-step write-ups of how to tune a q-jet? This is something I would like to know how to do since dad's truck has one and it don't seem to run exactly right.

you are correct the bolt patterns are different. BUT aftermarket intakes actually have both patterns drilled and tapped.

 

[HotRodPC]

Back up a minute, someone correct me if I'm wrong here but I don't think a spreadbore carb will even bolt to a squarebore intake. Spreadbore bolt pattern is longer front to back I think. The rear bolts may be a little wider too.

Also, back on the original topic/title of the thread, are there any step-by-step write-ups of how to tune a q-jet? This is something I would like to know how to do since dad's truck has one and it don't seem to run exactly right.

yes, they have dual bolt patterns but the Q jet on the wrong intake will have massive vacuum leaks since it won't fit the bore opening