Fix that Rich Running Quick Fuel

[Wbulk]

History
I am an older guy. Been working on carbs since high school in the 60s. I started tuning for altitude when I moved to Utah 35 or so years ago. I really got into detailed tuning about eight years ago when wide band gauges became reasonably priced and a friend who was Kirkham's foreman, showed me how Kirkham tuned carbs. I have tuned many Holley's, Quick Fuels and Edelbrock's since.

I have to say that I believe Quick Fuel is a great carb for the money if you have any of these few fixable problems take care of them. The adjustability is what you really need to do a good job of tuning, especially for higher altitude.

The Problems
1. Three of the last four Quick Fuel's I have worked on over the last two years did not have the small spring in the anti backfire valve that holds the check ball up. Without a spring the check ball falls down and can close off the vacuum passage. Vacuum keeps the power valve closed except when that engine vacuum falls below the PV setting. When it opens it dumps fuel through the PV restrictors into the main well, richening the main metering circuit. This symptom is the same as a bad power valve. It will make the engine run really rich when you may not want it to.
So, this is how it works. When the engine starts, vacuum pulls the ball down against the spring, opening the passage so the PV can close. The PV stays closed until the vacuum drops below the vacuum rating on the PV or the engine stops. Look at the metering block with the PV installed. The diaphragm side sets in a chamber in the main block. If that chamber cannot get and maintain vacuum the PV will open by the spring force in the valve. You can order a repair kit from Holley that comes with the correct size drill, ball and spring. You need a drill press to be safe.

Sometimes the problem can be an old hard gasket between the metering block and the main block that leaks air and cannot maintain vacuum. I have also found a poorly machined surface on the main block surface where the metering block mounts. I am now working on a Quick Fuel 830 SS that had that problem. This main block has QF and Proform cast into it. Most of the time you can fix it with a straight wide flat file. You can test the fix by installing the metering block and float bowl with a good gasket and tightening the four screws. With the throttle plate off apply vacuum with a Mity Vac to the small hole to the power valve chamber in the main block. This will test everything upstream and should maintain reasonable vacuum.

2. Quick Fuel used or maybe still uses an unusual throttle plate. I do not know if it has been changed as of this posting. On a 4150 style carb that has front and rear metering blocks with four corning idling the problem may be with the rear throttle plate body. In each secondary bore it has two idle passages. One standard screw passage for a normal 4150 four corner adjustment carb and a drilled idle passage below the idle transfer slot that would normally be for a 4160 style carb without a rear metering block, or a 4150 with the two front idle system only. The problem is with 4150 style with four corner idle screws. With this carb you have the two idle ports per bore that are active creating a conflict. You have that drilled idle port below the transfer slot and the idle screw port, both delivering idle fuel to the back barrels. So, when trying to adjust the rear idle screws you can get lost and not be able to adjust the rear idle circuits. You have fuel coming in the drilled hole below the transfer slot and fuel coming in the idle screw port at the same time. Not know this you cannot figure out why they won't adjust.

I tried three times to get Holley tech support who owns QF to explain how they wanted this to work without an answer until last month (7/23), when a tech was able to find the engineering drawings and told me he saw the 4150 four corner carb was supposed to have a plug in the drilled port below the idle transfer slot. This would eliminate the conflict and allow for normal adjustment with the idle screw.
About a year and half earlier I had done this on my own carb by filling the hole with JB Weld which worked really well. I did a QF 750 SS this week with great results. Everything adjusted like it was supposed to. Every QF I have worked on I have not seen that passage plugged.
If plugging that hole with JB Weld spray the hole out really well with carb or brake cleaner first. I then use a small glue syringe called Crystal FX that I get at Hobby Lobby. I file the metal needle tip to the angle I need to seal the hole and fill just the plastic chamber that holds the needle with JB weld. Do not put the JB weld in the upper tube where liquid would normally go. The JB weld is too thick. Press the JB Weld in slowly until you see it come out the idle transfer chamber looking from the top side of the throttle body. Stop when you see it just coming into the transfer chamber. Do not overdo it and make sure you do not leave JB Weld debris in the transfer slot. I use a magnifying headset to see what I am doing.

Good Luck

Pictures Added
The small hole above the transfer slot needs to be plugged for 4150 carbs.


Hole plugged with JB Weld


Anti backfire valve check ball up in correct position. If ball is down valve is missing spring.

[Wbulk]

John,
Private message sent. I'm not sure if that works.

[hauss]

wow, that was a lot of information. Still trying to rap my head around all of it. What about the two power-valves, getting rid of one, re jetting the secondarys, changing the air bleeds, checking the vacuum ordering the correct size power-valve, then further fine tune accelerator pump and if thats not enough, adjusting the electronic choke. I have tuned a lot of two stroke motorcycles in my day but, I must say the quick fuel has a lot of bells and whistles not easy for me.

[Wbulk]

Yes it is, but only if you want to do it right. The alternative is take what you get out of the box and accept what you get.

[hauss]

You meant to say easy for you I said not easy for me . I wish you lived closer sounds like you know your stuff. I am still learning I have got it so I can go to 6000 ft and not foul plugs and still run ok at sea level but I know I do not have the top end punch I used to before I leaned it out.

[sjdave]

I have been fighting "rich" idle for years on my Quickfuel SS750 on a 347 cu in build. Over the years with some jet tweaking and lots of advance it idles but very rich. Kind of gave up until I saw this thread, was thinking about converting to Fuel Injection this winter.

WOW....you nailed it, I have both issues on my Carb, extra fuel holes for NON metering block on secondary side and NO spring in the backfire check valve.

I used some some .023 welding wire and super glue to plug the two drilled passages, waiting for a spring to arrive from Holley for the anti backfire ball check valve.

Can't wait to get it back together and see if my Cobra doesn't choke me to death in the garage.

Thank You, Thank You!!

[Buddy Rawls]

When we have a rich idle with otherwise tuned in carb, it’s usually because primary side relationships aren’t right. (Throttle plate angle transfer slots and idle mixture). For a quick fix, we rough it about where it should be, then adjust the secondary idle position, till you can get tunability on the primary side. You can get more or less air into the plenum easily with no fuss or muss. Many of the carbs now have a fully accessible secondary idle too.

[fordracing65]

Buy a pro systems carb next time and be done with the problems.

[Wbulk]

sjdave,
Can you imagine how many of these carbs are out there with this problem? Just make these simple changes and things are great.

[Screaminchicken]

WBulk, thank you for this post, it has helped me greatly.
In 2011 i bought a Quick fuel SS-750 AN mechanical secondary carb
It ran rich had a flat spot couldn’t tune it for Sh$t and no one could tell me what was wrong it smelled like raw gas constantly and would leave a black cloud whenever you would stomp on it fuel milage was horrible. I followed the instructions on this post to the letter front had blow out protection check ball but no spring placed a spring in it from holly..
I noticed that secondary does not have a power valve but the base plate had the huge hole where the blow out prevention check ball and spring should be. Opened wide i am assuming it would suck air or fuel so i installed the check ball spring and brass plug just in case. Well i installed the carb on the engine it started right up made adjustments and it runs like a completely different carb i was able to use a vacuum gauge and adjust all 4 corners having a HG vacuum of 10-12 before the carb would only hold maybe 5hg of vacuum.. i would have to keep idle at 1000-1500 at idle to keep car running now it will hold at 500 rpm and i can drop it into gear and it stays at 500 amazing! I can not wait to get it out and run it see how it does and see what gas milage i get….

[cycleguy55]

Originally Posted by Screaminchicken

WBulk, thank you for this post, it has helped me greatly.
In 2011 i bought a Quick fuel SS-750 AN mechanical secondary carb
It ran rich had a flat spot couldn’t tune it for Sh$t and no one could tell me what was wrong it smelled like raw gas constantly and would leave a black cloud whenever you would stomp on it fuel milage was horrible. I followed the instructions on this post to the letter front had blow out protection check ball but no spring placed a spring in it from holly..
I noticed that secondary does not have a power valve but the base plate had the huge hole where the blow out prevention check ball and spring should be. Opened wide i am assuming it would suck air or fuel so i installed the check ball spring and brass plug just in case. Well i installed the carb on the engine it started right up made adjustments and it runs like a completely different carb i was able to use a vacuum gauge and adjust all 4 corners having a HG vacuum of 10-12 before the carb would only hold maybe 5hg of vacuum.. i would have to keep idle at 1000-1500 at idle to keep car running now it will hold at 500 rpm and i can drop it into gear and it stays at 500 amazing! I can not wait to get it out and run it see how it does and see what gas milage i get….

I certainly appreciate you want to get it running properly, but if you're chasing fuel economy in a Cobra you may have the wrong vehicle.

[Unique427]

Originally Posted by cycleguy55

I certainly appreciate you want to get it running properly, but if you're chasing fuel economy in a Cobra you may have the wrong vehicle.

Very true.
"Cobra Fuel Economy" qualifies as an oxymoron like these:

Jumbo Shrimp
Military Intelligence
Original Copy

[N2Cobras]

Originally Posted by cycleguy55

I certainly appreciate you want to get it running properly, but if you're chasing fuel economy in a Cobra you may have the wrong vehicle.

I measure SPG instead of MPG, my smiles as I shift thru the gears, all those from those who stop to admire and ask questions, thumbs up while on the road (especially from a cop when your at least 20 MPH over the limit ), etc.

[cycleguy55]

Originally Posted by n2cobras

i measure spg instead of mpg, my smiles as i shift thru the gears, all those from those who stop to admire and ask questions, thumbs up while on the road (especially from a cop when your at least 20 mph over the limit ), etc.