Advice building carb

[CultClassik]

Hi all, I'm new here.  Figured this forum would be best for QJ advice.

So I have the book, but I'm not super confident in my newly acquired knowledge

I have a 1979 C10, 350.  Original carb from what I can tell.  I rebuilt it about a year ago with a kit from Napa but it's pretty sad.  The engine was rebuilt stock before I bought the truck.  It was such a dog!  I swapped on new Vortec heads and an Edelbrock vortec performer, with headers and dual exhaust.  It's still not super hot and I know it's a truck and just a 350, but I think it's got a lot more to go. 

I've recently installed list springs, weights and an adjustable vacuum adv can and dialed in my timing, 12 base and 36 all in @3k rpm.  I converted to electric choke which never seemed to really work.  The other day I found my pull off was bad.  Swapped that on and it started up pretty decent (it's been chilly here, once it drops below 70 or so the truck is a lot grumpier that usual).  The engine pulls about 16in of vacuum at idle so it's pretty tame.

Along with dialing in the carb for best performance, I'd like to see what I can do about the fuel situation - as in if you don't start it every day, it takes a bit of cranking to get it going again, assuming I'm losing the fuel in the bowl somehow.

On to specs.

Engine: 79 low comp 350 (8:1?) .030 over.  Now with Vortec heads and Felpro blues, guessing around 9:1 comp.  Edelprock Performer Vortec.

Cam:
Lunati Voodoo 120701
V256H12
Advertised Duration (Int/Exh): 256/262
Duration @ .050 (Int/Exh): 213/219
Gross Valve Lift (Int/Exh): .454/.468
LSA/ICL: 112/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1000-5500

Carb: QJet 17059206

I was looking at recipe 1.  This is a single main air bleed carb?  I'm sure most of you are familiar with the recipes.  I already have the larger needle and seat and a brass float (I didn't replace the plastic one last time).  I'm trying to decide on which jets, rods and hanger to pick up.  When I re-rebuild I'll check the things like primary butterflies at WOT etc.  Any guidance that anyone can give will be greatly appreciated!

-Chris

[Bigal442]

Hi Chris,

Curious if you have specs on the carb as sits since you had it apart previously? So many old carbs have been modified at some point. At a minimum you could quickly get the secondary rod letters and hanger letter as a first step. Based on what you describe it doesn't sound like you could go too wrong with Recipe #1 as you said.

Also, can you give us some idea where the improvement is needed. (I.e. Idling vs. part throttle response vs. wide open throttle or multiple areas). Just trying to get more info on your situation. I'm not an expert by any means but glad to help if I can.

Al

[Ethan1]

Hi all, I'm new here.  Figured this forum would be best for QJ advice.

So I have the book, but I'm not super confident in my newly acquired knowledge

I have a 1979 C10, 350.  Original carb from what I can tell.  I rebuilt it about a year ago with a kit from Napa but it's pretty sad.  The engine was rebuilt stock before I bought the truck.  It was such a dog!  I swapped on new Vortec heads and an Edelbrock vortec performer, with headers and dual exhaust.  It's still not super hot and I know it's a truck and just a 350, but I think it's got a lot more to go. 

I've recently installed list springs, weights and an adjustable vacuum adv can and dialed in my timing, 12 base and 36 all in @3k rpm.  I converted to electric choke which never seemed to really work.  The other day I found my pull off was bad.  Swapped that on and it started up pretty decent (it's been chilly here, once it drops below 70 or so the truck is a lot grumpier that usual).  The engine pulls about 16in of vacuum at idle so it's pretty tame.

Along with dialing in the carb for best performance, I'd like to see what I can do about the fuel situation - as in if you don't start it every day, it takes a bit of cranking to get it going again, assuming I'm losing the fuel in the bowl somehow.

On to specs.

Engine: 79 low comp 350 (8:1?) .030 over.  Now with Vortec heads and Felpro blues, guessing around 9:1 comp.  Edelprock Performer Vortec.

Cam:
Lunati Voodoo 120701
V256H12
Advertised Duration (Int/Exh): 256/262
Duration @ .050 (Int/Exh): 213/219
Gross Valve Lift (Int/Exh): .454/.468
LSA/ICL: 112/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1000-5500

Carb: QJet 17059206

I was looking at recipe 1.  This is a single main air bleed carb?  I'm sure most of you are familiar with the recipes.  I already have the larger needle and seat and a brass float (I didn't replace the plastic one last time).  I'm trying to decide on which jets, rods and hanger to pick up.  When I re-rebuild I'll check the things like primary butterflies at WOT etc.  Any guidance that anyone can give will be greatly appreciated!

-Chris

 Welcome to CHP!

 Stock specs of that carb were .072" Primary Jets, 52M Primary Metering Rods, "K" Secondary Metering Rods and DR Secondary Metering Rods.

[CultClassik]

Thanks guys, and thanks for those specs!  I knew I'd seen them somewhere but wanted to be sure!  Original or not, I'm sure the carb is stock but when I was rebuilding it I didn't pay attention.  That was pre-cam and heads days so I wasn't concerned with more than stock function.

I actually seem to have the idle pretty good now.  Pretty much all around power seems down though.  I'm guessing this engine should make 280-300 horse and more in torque but it's feeling lacking from take off all the way up.  I started to play with the APT adjustment but its hard for me to notice any difference there.  The plugs look decent, maybe a little lean (which is what I'd except given the cam change from stock).

Now if I'm going with recipe one, should I just go on the big end?  I.e. it says .074-.076 main jets for single main air bleed carb, so go with .076 and approx .046 rods - and then I can fine tune with APT or am I misunderstanding?  The book has helped me learn quite a bit about the carb function but given all the different models I've gotten a bit confused at the same time

[Bigal442]

I am a newbie as we'll but tend to have the opinion of just changing out your jets to a size or so bigger and keep your stock (52m) rods, if this is what's still in there. For example, going from 72 jets to 74. This would then flow more fuel. Also check your main air bleed size to make sure they correspond with what's in the recipe.

Something else you could try just to confirm your engine wants more fuel. You could just change out the secondary rods to something that will flow more gas and see how she runs at Wide Open Throttle. Assuming the carb is still on the truck, this allows you to try something in 5 minutes. While it's true that the various systems overlap and work together this seems like it would be a good test to try. If your engine is fuel starved I would think it would have to run better at WOT. Cliff can provide guidance for which rods and everything else. You might also consider a faster pull-off as long as you're ordering rods.

[Ethan1]

Welcome to CHP!

 Stock specs of that carb were .072" Primary Jets, 52M Primary Metering Rods, "K" Secondary Metering Rods and DR Secondary Metering Rods.

 Sorry, "K" Secondary Hanger. Not Secondary Metering Rods.

[429bbf]

cliff would say start with a complete overhaul and good parts . throw the brass float away. did you try the tip in . this will tell you if your close without changing a bunch of pieces for practice. fwiw

[CultClassik]

Yes, complete re-overhaul is planned!  What's wrong with the brass float?  I was under the impression that they were more durable than the plastic type with ethanol blend fuel?

Yes, I did the tip-in and it seemed ok.  The plugs look decent but a little lean.  I assumed going from the really lame stock cam and heads with ~8:1 comp to the (still mild, but quite a bit more than stock) Voodoo cam and Vortec heads with ~9:1 compression would like at least a little more fuel than stock so I'm assuming jets, rods and hanger are going to be needed?

[Ethan1]

Yes, complete re-overhaul is planned!  What's wrong with the brass float?  I was under the impression that they were more durable than the plastic type with ethanol blend fuel?

Yes, I did the tip-in and it seemed ok.  The plugs look decent but a little lean.  I assumed going from the really lame stock cam and heads with ~8:1 comp to the (still mild, but quite a bit more than stock) Voodoo cam and Vortec heads with ~9:1 compression would like at least a little more fuel than stock so I'm assuming jets, rods and hanger are going to be needed?

 I actually prefer the brass float over the nitrophyl. The nitrophyl floats are hard to tell if there bad anyways. JMHO

[Cliff Ruggles]

Brass floats are a disaster waiting to happen, and they do not provide the same fuel level as the nitrophyl floats.

We installed one brass float this year, in a 2bbl application because nothing else was available.  About a month after sending the carb out, the new owner called and said it was flooding.  The new float was full of fuel and sitting on the bottom of the bowl.  The failure rate is very high for brass floats, at least from what I've seen here, so we avoid them.

I've had zero float failures with the new closed cell material and any type of fuel, even in straight alcohol and E-85...FWIW....Cliff