I need help tuning my Quadrajet!!! *UPDATE*

[BigOrange90Jimmy]

It's a brand new "rebuilt" carb that I purchased from a race shop for my stock 350 w/headers. It's running rich, fouling out some of my plugs. I have an intermittent misfire (probably from the plugs) and it burns a massive amount of fuel. I know nothing of how to tune it, and I'd rather not tear into it without knowing what to look for. I've been reading that florida4x4 page all about the quad, but that's almost too much for me.

 

[ZooMad75]

Go to Barns and Noble and get the Book called "Rochester Carburators". Its By Doug Roe I belive and published by HP Books. Its the best book out there for tuning/rebuilding q-jets as well as a couple other Rochester carbs like the 2jet.

If it's running fat at idle you might need to lean out the idle mixture screws. If it's running fat at part throttle and WOT you probably need to make an adjustment to the Main Meetering rods/jets/hanger combo. Thats where the book comes in handy. It has all the code breaking of what size the rod is that is marked "ABC" and helps you match it to the right sized Jet and correct length meetering rod hanger.

I say getting the book is money well spent in the long run.

 

[1-ton]

That is why I stay away from rebuilt quadrajets. Often times the fuel well plugs on the bottom plate get so ragged out that no matter how much epoxy or ceramic coating you put over them, they dump raw fuel into the intake manifold like a bucket that has been blasted with a 12-gauge shotgun loaded with bird-shot.

 

[pauly383]

Go to Barns and Noble and get the Book called "Rochester Carburators". Its By Doug Roe I belive and published by HP Books. Its the best book out there for tuning/rebuilding q-jets as well as a couple other Rochester carbs like the 2jet.

If it's running fat at idle you might need to lean out the idle mixture screws. If it's running fat at part throttle and WOT you probably need to make an adjustment to the Main Meetering rods/jets/hanger combo. Thats where the book comes in handy. It has all the code breaking of what size the rod is that is marked "ABC" and helps you match it to the right sized Jet and correct length meetering rod hanger.

I say getting the book is money well spent in the long run.

The depth the rods can go into the jets can be adjusted with the APT , and most reputable rebuilds are drilled and tapped for a plug to allow external adjustment .

I have several tests from my emissions testing station when I ran my DD , that prove there is a LOT of improvement just leaning it out very little .

Do not touch this without counting how many turns .

 

[BigOrange90Jimmy]

Aight, that doesn't help me much. I'm at least 2 hours away from a Barnes and Noble, much less afford to drive there. (broke college student)

 

[3 on the tree]

Call the shop you bought the carb from. Tell them what's going on, and see if they can help you. A really dumb question-is the choke opening all the way????

 

[BigOrange90Jimmy]

Yep, it's open. I have a mechanical choke on it.

 

[1-ton]

My advice would be to take the carb back, and get your money. I know there are a lot of quadrajet lovers here (I think they are pretty decent carbs too), but too many rebuilt ones are junk IMHO. The fuel wells leak raw fuel (no matter how much ceramic or epoxy you put on them), and the throttle shafts are always worn out, which causes the throttle to hang partialy open, and vacuum leaks.

Many shops will claim they rebushing the throttle shafts, but if you read the teeny tiny print, there is always a disclaimer on this saying "if needed". It is funny how 99.9 percent of them do not need it...supposedly.

If you do not plan on doing any hard core wheeling, then get a brand new Edelbrock performer. They are reasonbly priced, and work pretty decent for a low to mid-performance street machine.

If you plan on doing some high angle wheeling, then stay awy from the Edelcraps because it will shut down at the most inoportune time...when you are on the side of a steep hill. Instead get the Holly Truck Avenger. It is much more expensive, but it works great for hard core wheeling.

 

[dyeager535]

My advice would be to take the carb back, and get your money. I know there are a lot of quadrajet lovers here (I think they are pretty decent carbs too), but too many rebuilt ones are junk IMHO. The fuel wells leak raw fuel (no matter how much ceramic or epoxy you put on them), and the throttle shafts are always worn out, which causes the throttle to hang partialy open, and vacuum leaks.

On top of this, the number of carb stampings out there (10's of thousands probably) proves that the Q-jets were never built one size fits all.

APT is only present in the later Q-jets (mid-late 70's, but not all vehicles even in the 80's) so it may or may not be something you can mess with. Everything that deals with tune on those carbs is/was vehicle specific anyways.

However, if it's running as bad as you say it is, more than likely there is something physically wrong with the carb outside of the tune. Idle mix is the easiest to mess with based on ease of access, anything outside of idle is dealing with carb internals. Not complex internally, but takes some effort to tune from the inside.

 

[BigOrange90Jimmy]

Well, I've searched and asked around Boone, and have been told about a fellow in Blowing Rock who is reportedly a "God" with Quadrajets. I'll take the truck to him and let him figure it out.

 

[BigOrange90Jimmy]

Took the truck to the shop today. Called the guy this afternoon, and he told me his diagnosis on it. It's not the carb at all. He said that the advance springs in the distributor were weak, and at 10* timing, the truck wouldn't even start. He said it was getting full advance before it even started, and the base timing that it was set on when it was brought in was -2*. He said he would put new, heavier springs in it, and then set the timing to 10*.

I would have NEVER figured it out on my own. I'm saying it was money well spent!