1985 c10 350 carb issues?

[smdepew1976]

Ok so here is my short story. I have a 1985 chevy C10 it had a 305 when I bought it. The 305 ran great no issues other than lack of power and inability to be really upgraded. I swapped a 350 in the other day. It has vortec heads on it stock 92 tbi short block except Lunati Camshaft with Advertised Duration 256/262, Lift 454/.468 the M code manifold/headers. I want to use the same quadrajet from my 305 since I know it works good. However after I do the cam break in. You must keep your foot on the gas just a little to keep it running. Now I know I could simply turn the idle screw up a turn and make it work but I just dont feel thats the correct fix. Can anybody point me in the direction or how to properly tune a Quadrajet? I do have an Edlebrock 1406 would that be a better way to go? I really wanted to stay with a quadrajet but really just want it to idle and run right

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1985 C10 305 for now 350 waiting for installation

 

[Quadrajet Power]

You will need to modify the idle tubes in the quadrajet for it to idle with the cam and engine difference. Also change your power piston spring.

I am not sure what the idle tube size is in that quadrajet, but you can probably make it about .004 larger and be good for idle.

The quadrajet is a great carb to use. They were built specific for original engine application. When you change up the engine, the carb needs to be re calibrated to match. it does require disassembly and some tiny drill bits, but well worth it when you are done.

 

[smdepew1976]

Hmmmm well thats a little more than I'm totally comfortable doing those mods. Hmmmm well the 1406 ran rich on the 305 I guess I will try to get it on and tuned to run while I get my pennies together and send off my quadrajet. The whole carb question was why I got the Preformer intake since its the only vortec intake that accepts both square and spreadbore carbs. I think the Quadrajet is a much better carb for me and my driving style. This limited disability income makes it a long drawn out wait for funds


1985 C10 305 for now 350 waiting for installation

 

[Joe383]

I installed an AEM wide band on my last motor build. It has made tuning my carburetor way easier. I use to have an SA Design book on how to rebuild and tune Q-Jets that was awesome. I got it from Borders book store a few years back. There not cheep books ($25) but well worth the investment. It has great info on tuning the carb for larger cam. I would just swap to the Edelbrock. You might need a tuning kit for the Edelbrock if it was running rich on the 305 though, there is a good chance it will still run rich on you.

 

[firebane]

You will need to modify the idle tubes in the quadrajet for it to idle with the cam and engine difference. Also change your power piston spring.

I am not sure what the idle tube size is in that quadrajet, but you can probably make it about .004 larger and be good for idle.

The quadrajet is a great carb to use. They were built specific for original engine application. When you change up the engine, the carb needs to be re calibrated to match. it does require disassembly and some tiny drill bits, but well worth it when you are done.

Truth.

I have to do all this stuff to mine since I am running a bigger cam. The truck runs and does fine but it needs a lot of stuff tweaked to the carb now lol.

 

[smdepew1976]

Well I only assume it ran rich. With nothing else changed except quadrajet to 1406. I went from about 17-18 mpg to 12-14 mpg and I got most of the Edlebrocks tune kit but even tho I can turn a wrench pretty well I have only worked on stuff since the early 90s and most has be fuel injected. So carbs are one of my weak areas also Auto trannys


1985 C10 305 for now 350 waiting for installation

 

[DoubleDingo]

I was afraid of carburetors too, but once I got some books on the quadrajet, I was good to go. Just takes a little time to do them. Maybe half a day to assemble, adjust, install, and fine tune including setting timing after all is said and done. I would keep the q-jet if I were you.

 

[firebane]

Well I only assume it ran rich. With nothing else changed except quadrajet to 1406. I went from about 17-18 mpg to 12-14 mpg and I got most of the Edlebrocks tune kit but even tho I can turn a wrench pretty well I have only worked on stuff since the early 90s and most has be fuel injected. So carbs are one of my weak areas also Auto trannys


1985 C10 305 for now 350 waiting for installation

Edelbrocks need to be tuned EVEN more out of the box than a quadrajet.

 

[smdepew1976]

Well I have always liked SA books so I will just have to pick one up and see how well I can follow directions. I have 2 other quadrajets that I will try my luck modifying one of those. My concern with drilling on the 305s carb is the 305 ran pretty well it just leaked oil valve covers, intake front and rear oil pan and rear main seal. I want to keep the 305 incase something goes wrong with the 350 and if I drill on the carb It wouldbt work right back on the 305. I was hoping it would only need some air screw adjustments or something easy. Just my luck. Now I wonder what the other 2 quadrajets came off of...... Hmmmm


1985 C10 305 for now 350 waiting for installation

 

[firebane]

look at the stamped numbers and google lots of information on them.

 

[Joe383]

Nothing better than a properly tuned Q jet but nothing easer to tune than an Edelbrock. Something to look for not related to your problem is to make sure the secondary's are opening all the way cuz some times they don't on the Q jets they put on the 305s cuz they don't need as much air. One thing to consider though is that your Q jet is tuned for something with 100+ less HP than what your making and your Edelbrock is probably pretty close right out of the box. The only mods you should have to do to the Edelbrock is maybe some different metering rods. The Q jet has quiet a bit to the idle circuit and then your probably going to have to tune the primary and secondary fuel circuits after you get the idle figured out as well as modifying the choke pull off. Not a lot of money to tune but a lot of time and trial and error.

 

[smdepew1976]

17080213 0563 cpx looks like it came off a early 80s truck 350/400 so I think thats the one I will use. Now just off to find the book


1985 C10 305 for now 350 waiting for installation

 

[DoubleDingo]

I think I have the same carb. The numbers trigger a spot in my memory from when I was buying a kit to rebuild it.

 

[Joe383]

Make sure the throttle shaft for the primary's are not sloppy cuz every Q jet I have ever had has had some slop there and it can cause a small vacuum leak.

 

[smdepew1976]

Ok thanks guys for the help I believe Ive got it tuned pretty good. Now to try and figure out this adjustable vac advance needs to be set.


1985 C10 305 for now 350 waiting for installation