Adjusting my QFT...

[lippy]

First, I'm clearly no expert on carbs. But I have a QFT also and I've recently spent a lot of time learning and tuning. Here are some observations/opinions, but there are folks on this forum that know a lot more than I do.

- If you have a hot cam with overlap, the AFR meter will do you more harm than good until you get to higher RPM/load. Cams with overlap allow a lot of air and unburnt fuel through the exhaust at idle and the meter will read lean at low RPM/part load. If you then adjust the idle screws to get a "correct" reading, you actually will make the car rich at idle and this will throw off your tune across the entire range.
- As others have said, set your idle screws to achieve fastest idle and richen a bit if necessary to get rid of stumble.
- If you can't get the idle set correctly with the screws (unlikely), you may want to experiment with small changes in the idle feed restrictors.
- Go to larger squirters to address stumble when accelerating.
- Check your vacuum at idle and ideally when driving. My vacuum at idle, with the idle mixture screws set for fastest idle and vacuum, is about 7.5". When you open the throttle fully you drop the pressure differential between the atmosphere and the intake manifold and open the power valve. Higher numbered PVs open earlier and lower ones open later. I experimented and used a 4.5 and it works fine. You don't want it to be too close to idle or cruise vacuum or it will begin to open too early.
- The number on the PV dictates when it will open. The size of the PV restrictors controls how much fuel is given once it does open. If you are lean at WOT you can try to use larger PV restrictors.
- The idle circuit controls the amount of fuel given during idle. The idle circuit + main jets controls the amount of fuel given during cruise. The idle circuit + main jets + PV restrictors controls the amount of fuel given at WOT. I experimented with main jets after setting the idle to get me close on cruise and WOT, and then changed PV restrictors to richen up my WOT.
- The high-speed air bleeds (HSABs) control when the main circuit comes on, and also affects the mixture. Larger HSABs will make the main circuit come on at a higher RPM but will also allow more air into the carb, making it run leaner at this point. Since you need more air then fuel, my observation is that the engine is less sensitive to small changes in HSAB numbers. I put slightly larger HSABs in to make my mains circuit come on a bit later.
- I've learned the hard way that reading the plugs and feeling the engine is probably better than relying solely on an AFR meter.
- Although modern carbs are very adjustable, they are still pretty coarse instruments. Just try to get things reasonably close. You'll have a hard time dialing it in perfectly.
- Make one change at a time and keep good notes. Also mark down your baseline settings. This way, if things get to far off you can always to back to the baseline.

As I said before, a lot of the people on this forum are far more knowledgeable than I am on carbs, so feel free to correct anything above that's wrong.

[Austria_Cobra]

Thx guys!
The info about hot cam and overlap is new for me, that's why I do such threads, to get this sort of info!
The rest should be clear to me.
Now I have to start at the basline and that means ignition! The MSD is right out of the box. 18° and Advanced is comming at about 2100rpm. Has to be adjusted first. Also the maximum of the vac canister, does a bit too much.
After that I will start again with the carb.
I'll comb back on that.
Regards

[lippy]

I used the black (18 degree) bushing on my MSD distributor and dialed in total advance to about 36. This way my initial advance moved up to 18 so I could close my butterflies to achieve the proper transfer slot setting.

[Austria_Cobra]

Hi
what is it called at Summit, the gauge to check the size of the air bleeds, jets.. ?
thx

[Wbulk]

With your Quick fuel they usually send a small card with the stock jets and air bleeds listed. On a QF out of the box the restrictor jets in the main metering block may not be stamped with any numbers. You may have to call quick fuel or use a wire gauge to determine the size.
I have a quick fuel and love it. It is totally adjustable. I must say if you don't know carbs some of the information hear can be misleading. I am at 5,000 ft. above sea level and adjusted mine with my wide band O2 sensor, which are totally different than a narrow band that can mislead you. HOOK YOURS UP.

I am a old guy that was in high school and auto shop in the sixties and have worked on carbs for years. I used to jet carbs by reading plugs to but no more, I am converted. With fuels today it is very difficult to read plugs accurately. Also, with the wideband you can actually watch the gauge and determine the circuit you are in and tune that circuit one at a time. Of the 18 jets, air bleeds, and restrictors in that carb, I changed all of them. None were applicable at this altitude. I have to say with the wide band and a vacuum gauge, this is the best carb I have ever set up. It runs perfect in all circuits. It also took a few hundred bucks worth of gas to get to this point. I remember a thread Tom Kirkham did some time ago about tuning the power valve volume restrictors. With all the questions guys were asking he said several times you need a wide band to set it accurately.

Just a few examples, how do you know if you are in idle transfer or main metering around 2k rpms. You may think you are in main metering but may still be in the transfer circuit at that rpms. Or, you find at part throttle you have a slight bog that you think is a squirter issue, but it is actually going lean just before the power valve comes in and you actually need a higher number power valve. With a wide band and vacuum gauge hooked up you can actually see what's happening. I had my wide band hooked up, hung around my dash mirror with a mircofiber towel protecting the paint for weeks. I had a clear vacuum tube coming out the scoop and taped to the hood going to a vacuum gauge when I was working on power valve circuit. It is the best fit for new technology helping out the old. Take advantage of it.

[Austria_Cobra]

Hi Wbulk
Without AFR I do nothing, without it is like spark plug reading...
My QFT runs fine now after some changes, only a small enginge shakup under 2000rpm.
Just found out that my engine runs with 30° ignition... interesting.
Can you give me a link to summit for the wire gauge, cannot finde it. Thx
Regards

[Wbulk]

I use miro drills, but you can also use pin gauges.
SHARS 50 PC M0 011 060" Class ZZ Steel Pin Gage Set Minus New | eBay

[Austria_Cobra]

Originally Posted by Wbulk

I use miro drills, but you can also use pin gauges.
SHARS 50 PC M0 011 060" Class ZZ Steel Pin Gage Set Minus New | eBay

ordered thx

[Austria_Cobra]

Summery:

351W 427cui, 6400rpm (last Upgrad was done by AES Automotive Engine Specialties IL)

Comp Cam
PART #: 35-000-8
-> out of*http://www.compcams.com/catalog/COMP...11_417-493.pdf
ENGINE: FORD 351 WINDSOR
GRINDING INSTRUCTIONS
1*"" ""
2*"" ""
3
GRIND #: FW 3317F /3318F HR110.0
SPC INST 1:
SPC INST 2:
J. DIAM: STD INT EXH
VALVE ADJUSTMENT HYD HYD
GROSS VALVE LIFT .576 .600
DURATION @ .006*TAPPET LIFT 293 299
VALVE TIMING OPEN CLOSE
@ .050 INT 11 51
EXH 54 14
SPECS FOR CAM INST. @ 110.0 CENTERLINE
INT EXH
DURATION @ .050 242.00 248.00
LOBE LIFT .360 .375
LOBE SEPARATION 110.0
FIRING ORDER STD
ROCKER ARM RATIO 1.60 1.60

Now Ignition:
out of US it cam with 28° Initial and 11° Advanced. MSD . Curve will be measured soon.

I do not know which Gas it was setted up for? 100 Octane?
Here I run 95 Ocatan (could 97) but this is a difference here and US I heard of??

What is your opinion on Ignition ?