What are y'all running?
my qft 600 has 2 71's 2 70's and 4 31's.

Not too certain which I need to drop but I get 9.6 afr at idle...that's bad.

 

Changing main jets to change idle air/fuel ratio is counterproductive. As I recollect from the Fuel Lab where they used a wet flow bench a change in main jet only will change the A/F ratio about 2%. (They usually referred to the ratio as fuel/air - it makes calculations easier)

You are better off to pursue changes in the idle air bleeds and - in the case of multiple carburetion or heavily modified engines- idle transfer slots, and leave the main jets alone.

Also, do you have the proper PCV system?

 

I'm assuming the 70s are your primaries, 71s your secondaries?
What are the 4 31s? I'm not sure what that's referring to.

Jets won't affect your idle though. That's only your idle mixture screws.


Jetting has to do with how the carb's designed. It's designed to put X amount of fuel in the stream for Y amount of air. One 600 may need different jet sizes than another 600.

That said, of the two 600s I've had, one had size 64 jets stock and one had size 65. 70 seems really big, and more for a 750cfm or so. But, be sure to check QuickFuel's documentation to see if you have the correct size. Adjustments should only be minor, and deviating from the stock size should be for elevation and ambient temperature. I believe it's 1 jet size smaller for every 2000 feet above sea level and 1 for every 35° the temperature deviates from 70°.

 

Okay. I don't know what else it could be, my air bleed screws,( four corner idle circuit ) only help/ hurt drivability. They don't do anything to my idle afr.

I have no clue what the 31's are either. They are between the 70's on the primary and 71's in the secondary.

I'm about to call qft and ask.

My fuel bowl sits within and 1/8 of an inch of the middle. I'm gonna see if moving it will help it at all.

Are the two "needle point" tubes that come out of the top my breather tubes?

I'm sick of loosing all my fuel after letting it sit for a day or two.

 

The 31's are the idle air bleed screws, I was wrong. They work like jets to allow x amount of air in to the intake. So if I change them a decent gap up like I'm gonna shoot for a 33-35 and see what that does at idle then tune from there. I just hope someone has them in stock...

 

Can you post up some pictures?
I'm not sure what you mean by between the primary and secondary. There's two different metering blocks, one for each side. The primary metering block has some restrictions in it for the power valve and the idle feed. The top of the carb, down in the air horn, has air bleeds. There's also the accelerator pump squirter.

What are the 31s? Where'd you get the number from? Is this info they gave you, or are you reading it off of the jet itself?


If you turn your idle mixture screws all the way in (be careful to only gently close them, never tighten them), does your engine die? It should.


The two tubes that come out the top are breather tubes for the fuel bowls. Air has to come in so that fuel can go out, and visa versa, or they'll be a vacuum. Kinda like the breather on your gas tank.


You shouldn't be losing any fuel when it sits. How do you know it's losing fuel? Are the fuel bowls dry?

 

Oh okay, that makes sense. If you have too much fuel coming in on your idle, that can make a difference. Your idle feed restrictions (which are in your metering block) have a LOT of affect on your cruising AFR. I know on the spreadbore I was working on, they affected my cruise AFR all the way up to 60 - 70mph. They're not just for idle...



One thing I've seen mentioned a lot on carb tuning sites, and is what I plan to do for mine when I get it set up for adjustable air bleeds, is to get a full set of micro drill bits.

Then, go to: McMaster-Carr
and get some "brass set screws" that are the same thread pitch as the changeable air bleeds. Drill a bunch of your own.
When the air bleeds are $5 a pop, you'll save a TON of money.

 

These are in the top of my carb. I have 2 jets per bore. All changeable without removing anything but the air cleaner. My issue is that I wanted to drive the truck home this weekend so I can drive it legally( need it inspected to get reregistered....) But no where can get jets in that quick or that that small.

I will deff look into that. And yes my idle circuit goes up to about 1400rpm. Which will be about that fast too.

yes my fuel bowl sight glass I can visibly see it is down, weather it is from the heat or just the fumes slowly leaving I don't know yet. I do have a heat shield and a heated intake spacer on it now so we will see if that changes anything.

 

Hey that's a good idea. I've been buying the expensive blank air bleeds. Do you just let the set screws bottom out in the channel? The bleeds have a head that seats on the casting.

 

The two per bore are your air bleeds. One is for your idle, and one is for your high speed.
These meter the amount of air that goes in.

You can lean it out by making these larger, but changing the air bleeds also changes other characteristics of your carb, such as when the idle circuit comes in, and when it transfers to the main circuit (your jets).

On the other end of the idle air bleeds, are your idle feed restrictions in the metering block. Yours should be changeable due to it being a QF carb. You can also lean out your idle mixture by making this fuel restriction smaller.

On the other end of the high speed speeds are your main jets.


It's all a big balancing act, so take your time with it. Make small changes and watch your wideband.

 

I wouldn't think they'd need to bottom out, just that they go in far enough to seal the threads and don't back out. I planned on experimenting with a couple different lengths to see which ones work the best, but haven't gotten my carb down to the shop to have him drill and thread it yet.

 

I presume you are using 10-32s?

 

Me?
I haven't set mine up yet for adjustable air bleeds and restrictions, but plan to. Lots of carb tuning forums I've read have mentioned this trick so it sounded like a good one to share.