Need help tuning quick fuel carb! - Vintage Mustang Forums

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post #1 of 41 (permalink) Old 09-26-2015, 08:55 PM Thread Starter
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Need help tuning quick fuel carb!

65 stang. W/289 a code 4speed manual. Recently I put a brand new quick fuel slayer 600 4bbl. On it. The old holley was trashed. At first I struggled with a vac leak at the base gasket. Pretty sure I got that licked. Only issue. Lowest idle it would do was 700 and that's with the main throttle screw all the way out. I sprayed carb cleaner everywhere.. no leaks found. If I pull off one of the tiny vac caps it sores to 1200 rpm. The brake booster cap makes it idle at 2000. So I don't think I got leaks. I have the vac advance dist vac going to one of the vac ports provided on the carb. If I pinch that vac the idle will lower 100 rpms. Also my issue now... I'm trying to lower the idle by turning the 2 screws on the sides of the front metering block. I have no clue what these screws are but I did effectively lower the idle to 500. But the screws are basically turned all the way in. Maybe out 1 turn each. Then I set hot idle with the main throttle adjust screw to 700rpm. But now it smokes black... so I tried backing the screws back out but my idle is fast now.... its it's still smokey and eye burning... I connected a vac gauge. At hot idle I got between 17 and 18. Needle kinda bouncing. I did achieve 23in vac by messing with thoes 2 screws... but idle speed was up to 900... and that's with main idle screw all the way out.. please help
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post #2 of 41 (permalink) Old 09-26-2015, 09:52 PM
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Does the slayer have their 4 corner idle circuit? My hr series does and I thought there were 4 idle screws. If you just playing with two, and there are 4 that might be your issue. 700 rpm isn't too bad though, that is where you set and auto in gear.

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KC 331 Stroker w/ KC LH17 195cc, RPM Intake and QF680 carb
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post #3 of 41 (permalink) Old 09-26-2015, 11:13 PM
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Grab your installation instructions and adjust your mixture screws...either 2 on either side of front or, if you have "4-corner-idle"...all four using a vacuum gauge. Like it says, 1/4 turn alternating each screw so that no screw will be in/out more than 1/4 turn from any other.... THEN look for a secondary idle stop screw. In the image shown below, at the very top you'll see a spring-loaded adjustment screw sticking straight up... you'll probably have to look down between your secondary vacuum motor and the carb housing to see it...

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post #4 of 41 (permalink) Old 09-26-2015, 11:35 PM
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Slayer - primary metering block only, vacuum secondary, no secondary metering block.


The small screws on the sides of the metering block are idle fuel. In is lean, out is rich. The general rule of thumb on initial set up is to turn them in gently until they just lightly seat(start to snug) and then back them out 1 1/2 turns. Re-adjust the bigger screw on the linkage then. That is idle speed, throttle opening, air, affects rpm. Plugs should run fairly white at idle and you shouldn't have an exhaust smell unless you are running a biggish cam.

If you can pinch the distributor vacuum hose while connected and it affects your idle, it sounds like the hose is leaking or the distributor vacuum advance pot is leaking.

331 solid flat cam, rings and bearings break in run up.
https://www.youtube.com/watch?v=3MNjb-AiWec
331 break in complete and is waiting on me to finish the body work
https://www.youtube.com/watch?v=YhnOk5FCBkE

Last edited by macstang; 09-26-2015 at 11:40 PM.
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post #5 of 41 (permalink) Old 09-26-2015, 11:39 PM
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Quote:
Originally Posted by macstang View Post
If you can pinch the distributor vacuum hose while connected and it affects your idle, it sounds like the hose is leaking or the distributor vacuum advance pot is leaking.
...or the spark advance hose is connected to a manifold vacuum port...which is just fine.
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post #6 of 41 (permalink) Old 09-26-2015, 11:42 PM
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Ah, pinching it off could affect the timing advance which would probably alter idle rpm.

331 solid flat cam, rings and bearings break in run up.
https://www.youtube.com/watch?v=3MNjb-AiWec
331 break in complete and is waiting on me to finish the body work
https://www.youtube.com/watch?v=YhnOk5FCBkE
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post #7 of 41 (permalink) Old 09-27-2015, 12:09 AM Thread Starter
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Sweet! Thanks for the help. Exactly what I needed. Going to adjust it up tomorrow. I just feel that unless the screws are all the way seated... then I will have a high idle. Forgot to add.. tho I don't think it matters.. I have not wired up the electric choke yet. It did start to open when the engine warmed up anyway... but only 1/4inch... I can open it all the way by hand but nothing happens... also there is a port on the front metering block that's capped. It does not pull a vacuum. What's that for?
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post #8 of 41 (permalink) Old 09-27-2015, 07:37 AM
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What is your initial timing?

Timing needs to be sorted first before carb tuning.

1973 Mustang Convertible
460 D0VE-C Heads w/CJ size valves, Lunati voodoo 227/233 cam, Edelbrock performer rpm manifold, FPA headers, Holley 950 HP carb, C6 w/2500 stall converter, 3.25 trac lock
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post #9 of 41 (permalink) Old 09-27-2015, 08:29 AM
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Quote:
Originally Posted by 65vertable View Post
65 stang. I'm trying to lower the idle by turning the 2 screws on the sides of the front metering block. I have no clue what these screws are ....
Those are the idle mixture screws, they can affect idle rpm, but that's not their primary purpose.

Step 1: Read the instructions!

http://www.quickfueltechnology.com/I...ons_Rev._1.pdf

Step 2: Hook up the electric choke, or set it so it's fully opened and won't affect the idle setting.

Step 3: Set your timing to factory spec or around 10* BTDC.

Once you've accomplished that, follow the very specific tuning sequence in the manual. It's pretty much the same all around for any car.

If you do not have a vacuum gauge, I suggest you buy one.

Regarding vacuum advance: some like to run full manifold vacuum, others like myself prefer timed or ported vacuum. Each requires it's own specific timing setup. Your car was originally setup with ported vacuum, in that the vac advance only worked once the throttle plates were opened. I suggest, for simplicity, that you run it this way. At idle, you should not have any vacuum present at the distributor.

Nothing worthwhile is ever quick, cheap or easy, those that can't do, complain

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post #10 of 41 (permalink) Old 09-27-2015, 09:57 AM
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Please keep us up to date on your progress, I'm thinking about getting a quickfuel carb myself.

Matt
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post #11 of 41 (permalink) Old 09-27-2015, 10:18 AM
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Quote:
Originally Posted by Hemikiller View Post
Those are the idle mixture screws, they can affect idle rpm, but that's not their primary purpose.

Step 1: Read the instructions!

http://www.quickfueltechnology.com/I...ons_Rev._1.pdf

Step 2: Hook up the electric choke, or set it so it's fully opened and won't affect the idle setting.

Step 3: Set your timing to factory spec or around 10* BTDC.

Once you've accomplished that, follow the very specific tuning sequence in the manual. It's pretty much the same all around for any car.

If you do not have a vacuum gauge, I suggest you buy one.

Regarding vacuum advance: some like to run full manifold vacuum, others like myself prefer timed or ported vacuum. Each requires it's own specific timing setup. Your car was originally setup with ported vacuum, in that the vac advance only worked once the throttle plates were opened. I suggest, for simplicity, that you run it this way. At idle, you should not have any vacuum present at the distributor.
+1. I've tried both ports and the timed vacuum port is the one you should use.

John

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post #12 of 41 (permalink) Old 09-27-2015, 02:01 PM Thread Starter
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I'm not supposed to have vac to dist at idle? How do you do that?? Their is constant vacuum while it's running... their is one nipple on the carb that's capped that at idle does not draw vac. But I didn't see if it draws vac off idle... I think I have a timing light somewhere.. I timed it by ear 4 years ago and haven't touched it since. I'd bet it's advanced quite a bit.

So far for the quick fuel carb.. I love it. Fut and finish are top notch. Floats are set out of the box.. no tuning needed for a 1 crank start out of the box... I think I have other things going on causing my issues.. none of it being carb related... user error. I come from an age of direct injection. Everything cpu controlled. Hard to use stones as tools when your used to fixing cars with a laptop....

I will keep posted as I tinker. Thanks everyone for the help.

First thing I'm going to set timing at 10*btdc at hot idle. Then screw both screws in all the way. Slowly back them out till idle raises then starts to lower again.. adjust throttle stop screw...

Just have to figure out this no vac to dist at idle thing... I need a tuned vac port? Maybe the one I was talking about on the carb that doesn't have vac at idle... dono
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post #13 of 41 (permalink) Old 09-27-2015, 08:53 PM Thread Starter
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Few things.. turns out that the vac port on the carb that has no vac at idle. Has vac if you crack the throttle. So I ran my dist vac to that. Got it warned up. Ran both mix screws all the way in. The out 2 turns. Right when idle starts to pick up.. then I adjusted base idle with main screw to 750. Warmed up. I checked timing. The mark on the damper is about half a pinky width on the right side of the pointer on the engine if your standing in front of the rad leaning down looking.. I didn't make any timing adjustments. That looks pretty close to me.. so it's idling smoothish. Revs up very quickly and briskly. No stumbling... but boy is it running rich. Smoking... leaving stains in driveway from exhaust gasses. And I noticed that smoke is comming out of the valve cover breather tube at a good rate. If I cup my hand over it. It will Acually build up a bit of pressure... dono...with this setup. Vac is holding at 17ish. Runs great.. just burns your eyes... also I was unable to find a 12 volt with key on wire for the choke. So the choke plate was 80% closed this entire time... I found a bunch of constant on wires. I found a 7 volt. And a 5 volt wire that come on with key... the wires on the back of the alt are either on constant or never on.. same with regulator/coil.
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post #14 of 41 (permalink) Old 09-27-2015, 09:56 PM
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There's no practical reason to use a timed spark port if your vehicle isn't subject to emissions testing. You'll idle cooler and smoother, albeit with a bit more HC (hydrocarbon) emissions, than "ported" vacuum.

Your idle speed issue is most likely caused by the non-functioning choke. If you're not going to hook up the electric choke right away either loosen the choke cap screws and turn the choke thermostat all the way to the "lean" end to keep the plate wide open or wire it wide open. With the choke plate even partially closed your fast idle cam will be in a position to control idle, instead of the curb idle screw, and your secondaries will be locked out.
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post #15 of 41 (permalink) Old 09-27-2015, 10:18 PM Thread Starter
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I plan to wire up the choke asap. I just can't find a switched 12v line. Anywhere.
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