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Thread: Srobinsonx2 Carb Tuning

  1. #1
    Senior Member srobinsonx2's Avatar
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    Srobinsonx2 Carb Tuning

    Ok, I have read books, forum threads, and articles, watched videos, and asked experts about tuning a carburetor. I have a basic understand but have never done this before. After doing research, I still have some questions. I hope to do two things with this thread. One, document my process with all the details. Two, I will asked questions and hopefully capture the answers here for all to share. I am sure most of the answers can be found in threads through out the FFR forums. But, I have not find them in one place that is simple to follow and in enough detail for this amateur. So, here we go.

    It might help if I share some information about my set up.

    - Engine is a Levy Racing Stage 4 347. I don't have specific part numbers or data. Per the website "steel crank, I beam rods, Forged pistons, Custom hydraulic roller cam, Victor Jr. cylinder heads, Victor 5.0 or Victor Jr. intake. It is 10:1 compression and runs on 91 octane pump fuel. Horsepower is 420 bench dyno with a properly tuned EFI or 450 with a Holley 650 pro series carburetor. 6000 rpm shift point with a 6500 rpm rev limit "

    Transmission is a T5 from Levy Racing as well. I think is it a "super alloy" to handle the higher power of the 347.

    Rear end is a Ford 3.55 rear end.

    Carb is a Quick Fuel 750 SS. It has mechanical secondaries with an electric choke. I have a 1/2" phenolic spacer under the carb to help with heat.

    Ignition system is MSD 6AL with MSD Blater 3 coil. I am using Taylor Thunderbolt spark plug wires.

    Timing is set to 14 degrees BTDC at idle and gets to full advance of 35 degrees between 3000 and 3500. I will verify this during the tuning.

    I will start on the tuning tomorrow. Hopefully this helps others.
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  2. #2
    Senior Member Gordon Levy's Avatar
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    The engine makes a bit more power than that now over when I wrote that. Pleases to start is power valve, float level and proper setting of the 4 corner idle circuits. Next would be possible jet and/or pump cam settings.
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    Senior Member srobinsonx2's Avatar
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    Thanks Gordon. More power......ME LIKEY!!! I am going to try and tackle all of those. I have a LM-2 wideband O2 meter coming. Hopefully I can get this baby all dialed in and have something that will make your proud.

    If you see me headed off the cliff, feel free to point out the error of my ways.

    Just out of curiosity, what do you think my engine will make at the wheels if tuned properly?
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  4. #4
    Senior Member Gordon Levy's Avatar
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    Depends on the dyno but 375+ isn't not out of the question.
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    bobl's Avatar
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    A couple of things to check before you get too involved in the carb. First make sure your timing is staying steady throughout the idle rpm range. If it moves due to slop, weak springs, etc. you'll never get it to hold a steady idle. Vacuum advance can wreak havoc on idle also, but it appears you do not have one. Secondly, open the choke setting all the way so it does not interfere with your idle settings. Once the idle is set you can readjust the choke. Only adjust idle after it's fully warmed up.

    If you cannot get a satisfactory idle, there are ignition boxes that have programmable timing curves and idle control which would certainly solve your problems.

    Bob
    Mk IV Roadster, 347/516 HP, 8 stack injection, Holley HP ECU, Astro Performance T5, 3-Link 4.10 gears, A/C, PS, PB Purchased 08/2015, Graduated 02/2017

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    bobl's Avatar
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    Question for Gordon. You've built and dyno'd many of this engine combination. Is the carb you send with that engine rejetted based on your testing, or is it right out of the box? Would you expect it to need rejetting in an installation like this? Shannon is at low elevation and I believe your shop is located at quite a bit higher elevation.

    Bob
    Mk IV Roadster, 347/516 HP, 8 stack injection, Holley HP ECU, Astro Performance T5, 3-Link 4.10 gears, A/C, PS, PB Purchased 08/2015, Graduated 02/2017

  7. #7
    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by bobl View Post
    A couple of things to check before you get too involved in the carb. First make sure your timing is staying steady throughout the idle rpm range. If it moves due to slop, weak springs, etc. you'll never get it to hold a steady idle. Vacuum advance can wreak havoc on idle also, but it appears you do not have one. Secondly, open the choke setting all the way so it does not interfere with your idle settings. Once the idle is set you can readjust the choke. Only adjust idle after it's fully warmed up.

    If you cannot get a satisfactory idle, there are ignition boxes that have programmable timing curves and idle control which would certainly solve your problems.

    Bob
    Thanks Bob. Here is what I have for timing. 14 degrees BTDC at idle. I have checked this a couple of times over the past months and it is always 14. The timing goes to 35 degrees BTDC when the rpms get above 3000 rpm. These don't seem to change.

    I did open the choke today to make sure I wasn't setting the idle while on the high idle cam. I then set it back where I had it. Tried a cold start after my idle tune today with much better results.

    Thanks for keeping an eye on me. If I can get my engine to run half as well as yours I will be happy. Any advice or oversight is appreciated. We need to get together and go for a drive.
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    Senior Member srobinsonx2's Avatar
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    Idle Circuit Tune

    Started on my idle tune today. First things first. I remove the carb and made sure my T slots were set properly. According to the experts the slot should be 0.04-0.06 inches. Seems pretty tough to measure so I used the rule of thumb that the T slot should be a square. I started with the primaries (front). Here is where I ended up with the fronts.



    If you notice the T slot on the right is open more than the T slot on the left. Is that normal? I kind of split the difference and had the left less than a square and the right just a little more than a square. Let me know if something looks off. I adjusted this T slot exposure by turning the primary idle speed adjustment screw. For those that don't know where this is (like I did), here is where it is (circled in red)



    Next I decided to expose a little bit of the secondaries (rear of the carb) T slots. I had these completely closed before and could not get a decent idle without opening up the primary idle speed adjustment. Here is where I set the secondary T slots. Again the one on the left is not as open as the one of the right. Same as the primary. Again this looks weird so let me know if I might have a problem. As you can see these are not quite a square.



    I adjusted this with the secondary idle speed adjustment screw. It is located on the bottom of my carb. Again it is circled in red.



    The red arrow on the right is pointing to the manifold vacuum port on the front of the carb. This is where I attached my vacuum gauge.

    After getting these all set, I turned the four corner idle mixture adjustment screws out to 1 1/2 turns and remounted the carb. I started the engine (started easily) and let it warm up to 180 F. I then let it run for another 5 minutes to make sure everything was up to temp. I then connected my timing light (which I am using to monitor rpms) and the vacuum gauge. I then started adjusting the idle mixture adjustment screws (IMAS). Here is what I did.
    - Started at the passenger rear IMAS and turned it in 1/4 a turn and looked at the rpm and vacuum. It went up so I turned it back to 1/8 a turn.
    - Turned the remaining 3 IMAS screws in 1/8 a turn.
    - Continued this process until I got the following readings on my rpm and vacuum gauge.



    - At this point I had all IMAS open 7/8 of a turn. When I made one more adjustment on the IMAS, the rpm and vacuum went down. So went back to the previous setting and stopped.

    In the picture the vacuum appears to be around 7 " of Hg vacuum. That isn't exactly correct. The average was actually 8" of Hg and was bouncing between 7 and 9.

    The rpms were average around 950 and bounced between 930-980. It idles very well.

    I took the car for a short drive and it ran very well. Seems to be responsive with no bog or stumble.

    I also got my LM-2 in today.



    I marked the bung location on the passenger side exhaust. I will remove that side pipe and get the bung welded in this week.

    Let me know if you see any mistakes or issues. Those uneven T slots are a little concerning but might just be my lack of knowledge. Thanks in advance for the help.
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  9. #9
    Senior Member Gordon Levy's Avatar
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    Out of the box, I can tune and set up a carb for here but I have found the air in different places way to different for me to take a good stab at it. Example, I built a car for someone in the northeast. I dyno tuned the car and set the carb very rich for my air feeling it would be close for where it was going. It wasn't, it was super lean so I always recommend proper tuning for you area.
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    Well Used Member boat737's Avatar
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    Time to show my ignorance. What is a T Slot? Can you point it out in your pictures? Is it an Idle only setting? Thanks.
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    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by boat737 View Post
    Time to show my ignorance. What is a T Slot? Can you point it out in your pictures? Is it an Idle only setting? Thanks.
    The "T slot" is slang for the Transition slot. It provides gas between the idle circuit and the other "main" circuits. The T slot actually looks like a slot and what I exposed is just the very bottom of the slot. You can see it in this pic. I have a blue arrow pointing to it.



    As you can see the one with the arrow pointing to it has more exposed than the one on the left. I don't know if this is correct so we will see what the experts say.

    Hope that helps. You just exhausted my knowledge on the old "T slot".
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    Senior Member Gordon Levy's Avatar
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    I have always used the 4 corner idle screws a bit different. I have found having all 4 set that same ends up being rich. I usually start the front at 1.5 turns and the rear at 1/2 turn. Using the fronts to get the idles where I want it and use the rears to smooth the idle out. I average 1.25-1.5 turns on the front and 1.4-1/2 on the rears.
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    Senior Member Gordon Levy's Avatar
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    What kind if vacuum are you making? I beleive that car comes with a 4.5 power valve and may require a 2.5.
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  14. #14
    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by Gordon Levy View Post
    What kind if vacuum are you making? I beleive that car comes with a 4.5 power valve and may require a 2.5.
    I am getting 8" of Hg at idle. Does a 4.0 power valve sound about right?

    Thanks Gordon.
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  15. #15
    Well Used Member boat737's Avatar
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    Quote Originally Posted by srobinsonx2 View Post
    The "T slot" is slang for the Transition slot. It provides gas between the idle circuit and the other "main" circuits. The T slot actually looks like a slot and what I exposed is just the very bottom of the slot. You can see it in this pic. I have a blue arrow pointing to it.

    As you can see the one with the arrow pointing to it has more exposed than the one on the left. I don't know if this is correct so we will see what the experts say.

    Hope that helps. You just exhausted my knowledge on the old "T slot".
    Thanks "S". I'm not getting into any engine tuning as of yet, still getting past the go-kart stage. I'm putting the body back on for the 2nd time soon, to put some miles on the car, at which point I'll need to address my 2 mpg issue. (I have 16 miles on the car, and it's gone through 7 gallons of gas.). I'll be following your thread with great interest. (although, my carb is a Holley 750, so... We'll see.)
    If Brute Force doesn't work, you're not using enough of it.
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    Srobinsonx2,

    I am at the same place you are and plan to work on the carb tuning this week. Interesting about Gordon's comment about tuning effected by different locals. My engine was built by Mike on the East coast and I'm in the Midwest. I checked my mixture screws setting the other day on my quick fuel HR 780 cm with vacuum primaries and secondaries. They were all at approximately 1/2 turn out. Should be interesting.

    But, I do have another observation. I see you have a 1/4" ID nose running from the right valve cover to the back of the carb (same as mine). It was mentioned to me that this could be a source of a vacuum leak and that i may want to consider capping the tube at the rear of the carburetor and venting the valve cover pvc to a catch can. Maybe the experts could weigh in on this??
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    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by ThickCobra View Post
    Srobinsonx2,

    I am at the same place you are and plan to work on the carb tuning this week. Interesting about Gordon's comment about tuning effected by different locals. My engine was built by Mike on the East coast and I'm in the Midwest. I checked my mixture screws setting the other day on my quick fuel HR 780 cm with vacuum primaries and secondaries. They were all at approximately 1/2 turn out. Should be interesting.

    But, I do have another observation. I see you have a 1/4" ID nose running from the right valve cover to the back of the carb (same as mine). It was mentioned to me that this could be a source of a vacuum leak and that i may want to consider capping the tube at the rear of the carburetor and venting the valve cover pvc to a catch can. Maybe the experts could weigh in on this??
    Thanks ThickCobra. I did remove and cap the large manifold vacuum line you describe during the idle tuning and it didn't change at all. I will keep your comment in mind. That might be a good trick if I see the idle performance change drastically.
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    Senior Member srobinsonx2's Avatar
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    A couple of questions for the group. Since I know my manifold vacuum at idle, I was going to get a new power valve coming my way. It appears that most carbs only have one power valve (on the primary side) but some can have two. Does anyone know what a stock Quick Fuel SS 750 has? As stated above, it is mechanical secondary and should be set up just like it was out of the box. So two questions:

    1. How many power valves do a need? 1 or 2
    2. Manifold vacuum is 8" of Hg and I was going to get a 4.0 power valve (the Quick Fuel "four door" type). Should I get a 3.5 and 4.0?

    Thanks.
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    Can you share where you sourced your LM 2 kit. And, it comes with a bung?
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    bobl's Avatar
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    That vacuum reading seems a lot lower than I would expect. Do you have the cam specs? You might double check for a vacuum leak. My engine makes 12" at 800 rpm idle and that's with the stack injection. My cam is 233/242 duration on 112 lsa. Gordon should know if that is what he's seen on that particular build before. Might be just the gauge.


    Quote Originally Posted by srobinsonx2 View Post
    I am getting 8" of Hg at idle. Does a 4.0 power valve sound about right?

    Thanks Gordon.
    Mk IV Roadster, 347/516 HP, 8 stack injection, Holley HP ECU, Astro Performance T5, 3-Link 4.10 gears, A/C, PS, PB Purchased 08/2015, Graduated 02/2017

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    Senior Member johnnybgoode's Avatar
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    One of the things you can do to make setting the idle easier is the take that secondary throttle stop set screw out from the bottom of the carb and turn it around and put it in from the top. You can then set the secondary stop from the top of the carb without having to take it off. Just hold the throttle wide open (with the motor off of course) and adjust the set screw from the top. I normally set the primary T-slot and then fine tune the idle with the that secondary set screw. Scott
    Last edited by johnnybgoode; 09-24-2017 at 01:55 PM.

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    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by bobl View Post
    That vacuum reading seems a lot lower than I would expect. Do you have the cam specs? You might double check for a vacuum leak. My engine makes 12" at 800 rpm idle and that's with the stack injection. My cam is 233/242 duration on 112 lsa. Gordon should know if that is what he's seen on that particular build before. Might be just the gauge.
    Thanks Bob. Maybe Gordon will chime I with some specifics or let us know if 8 sounds right. Just in case, I will get another gauge to verify.
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  23. #23
    Senior Member Gordon Levy's Avatar
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    8-10 is about right
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    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by ThickCobra View Post
    Can you share where you sourced your LM 2 kit. And, it comes with a bung?
    ThickCobra,

    I bought the LM-2 Kit from Amazon. Here is a link. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    It comes with all the components. This is the "complete" kit. Just a note, the kit I got did not come with the software. It appears it is now a download via their website. Hope this helps. Here is picture of the kit with all the parts.



    You can see it comes with the brain, an SD card, manual, power cord, O2 sensor, O2 sensor cable, bung, plug, OBDII cable, analog cable, and USB cable.
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    Quote Originally Posted by srobinsonx2 View Post
    ThickCobra,

    I bought the LM-2 Kit from Amazon. Here is a link. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    It comes with all the components. This is the "complete" kit. Just a note, the kit I got did not come with the software. It appears it is now a download via their website. Hope this helps. Here is picture of the kit with all the parts.



    You can see it comes with the brain, an SD card, manual, power cord, O2 sensor, O2 sensor cable, bung, plug, OBDII cable, analog cable, and USB cable.
    Srobinsonx2,

    Thanks much. I know you're working thru your issue, so I certainly appreciate you sharing.

    Jay
    Mk4 Roadster 20th Anniversary #8658. 04 of 20. 3.31 IRS.
    Forte 427 Dart, TKO 600, Quick Fuel 780 carb. Delivered 9/2/2015, First start/Go Cart 2/18/2017.
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  26. #26
    Senior Member srobinsonx2's Avatar
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    So I went ahead and ordered some tuning parts. Not sure exactly what I need so let me know if I am way off base.

    According to the specs for my 750 SS I have a 4.5 power valve, 74 primary main jets, and 84 secondary main jets. The idle air bleeds are 70 and the high speed air bleeds are 31. The air bleeds I verified.

    Here is what I have coming my way:
    - 4.0 and 5.0 power valve
    - 75-110 main jet assortment (2 of each)
    - 35-45 air bleed assortment (4 of each)
    - 75-85 air bleed assortment (4 of each)
    - fuel bowl vent baffles (I have a hard braking engine stall)
    - new vacuum gauge to check my current gauge.

    Carb tuning isn't really cheap but I can return some of this if I don't need it.
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  27. #27
    Senior Member Gordon Levy's Avatar
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    Bet you will end up with a 72 in the primary
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    Senior Member CraigS's Avatar
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    They really screw you on the air bleed assortment. The chance of needing 4 bleeds the same # I thought was about 1% so I ordered my bleeds individually. Kind of a pain though coming up w/ a nice box to keep them in. It's been a couple years since I had my carb off but I don't remember the T-slots being different left to right. Anyone have thoughts on that?
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    Seasoned Citizen NAZ's Avatar
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    Remember that when comparing vacuum readings with folks across the country there will be some differences due to altitude. Your vacuum gauge will read ~1" lower for every 1,000' of altitude ASL. So unless you're given a comparison vacuum reading at altitude it's going to be hard to make any valuable comparison. I live at 7,000' ASL and the vacuum reading on my car would seem very low to someone based in Florida.

    srobinsonx2, don't forget to purchase an assortment of accelerator pump cams and squirters (accelerator pump discharge nozzles) in addition to the other tuning parts.

  30. #30
    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by NAZ View Post
    Remember that when comparing vacuum readings with folks across the country there will be some differences due to altitude. Your vacuum gauge will read ~1" lower for every 1,000' of altitude ASL. So unless you're given a comparison vacuum reading at altitude it's going to be hard to make any valuable comparison. I live at 7,000' ASL and the vacuum reading on my car would seem very low to someone based in Florida.

    srobinsonx2, don't forget to purchase an assortment of accelerator pump cams and squirters (accelerator pump discharge nozzles) in addition to the other tuning parts.
    Thanks Naz. I forgot about the accelerator circuit. According to the carb 101 thread and my How to Supertune a Holley book, the accelerator circuit is the last thing to tackle. I will see if they don't have an assortment kit. Thanks again for the reminder.
    FFR MK4 Complete Kit #8952
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  31. #31
    Senior Member srobinsonx2's Avatar
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    Bung installed

    I got my bung installed today. I know.....that just sounds wrong. I had to do some searching but I found a shop that would tig weld on my stainless steel side pipes. Tig welding provides a very clean weld.

    Here is the bung installed.



    I positioned the bung so that the sensor would just clear the body. Here is the exhaust and sensor installed.



    I will work on tuning later this week. It is suppose to rain the next few days so no real chance for driving it appears.
    FFR MK4 Complete Kit #8952
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  32. #32
    Senior Member Avalanche325's Avatar
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    I certainly don't remember my T-slots being different. I think that is an issue that you need to deal with first. You could have a bent butterfly plate or shaft, or it could be as bad as a warped baseplate. If the mechanical settings are not right, nothing will be. One slot opened too much could make the idle screw on that side ineffective. You will be chasing your tail.

    It could be as easy as loosening the butterflies and reseating them. Or giving them a tweak. I swear they look crooked in your first photo. I would give QF a call on that one.

    My general advice:
    The real and true step one. If you don't have your carb settings card, write everything down. Keep a log of your changes.
    Timing first, carb mechanicals 2nd (you have something to look at here), then idle, etc.
    As you can already see, there are several different ways to tune a carb. Pick one methodology and stick with it.
    Don't jump off the tips and tricks cliff until you try all the down the middle tried and true things and have a specific issue. (I have seen forums with guys trying to fix their idle by changing main jets and drilling their butterflies.)
    If you changed all sorts of things and it is not getting better, put it back to factory and start again.

    Carb tuning is all part of the fun.
    Last edited by Avalanche325; 09-25-2017 at 08:56 PM.

  33. #33
    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by Avalanche325 View Post
    I certainly don't remember my T-slots being different. I think that is an issue that you need to deal with first. You could have a bent butterfly plate or shaft, or it could be as bad as a warped baseplate. If the mechanical settings are not right, nothing will be. One slot opened too much could make the idle screw on that side ineffective. You will be chasing your tail.

    It could be as easy as loosening the butterflies and reseating them. Or giving them a tweak. I swear they look crooked in your first photo. I would give QF a call on that one.

    My general advice:
    The real and true step one. If you don't have your carb settings card, write everything down. Keep a log of your changes.
    Timing first, carb mechanicals 2nd (you have something to look at here), then idle, etc.
    As you can already see, there are several different ways to tune a carb. Pick one methodology and stick with it.
    Don't jump off the tips and tricks cliff until you try all the down the middle tried and true things and have a specific issue. (I have seen forums with guys trying to fix their idle by changing main jets and drilling their butterflies.)
    If you changed all sorts of things and it is not getting better, put it back to factory and start again.

    Carb tuning is all part of the fun.
    Avalanche325,

    Thanks on confirming my fears about the T slot concern. I will call Quick Fuel tomorrow (well, Holley now). My fear is that the baseplate is warped. If you look at both the secondaries and primaries, they both have the same issue but on opposing sides. The drivers primary and the passenger secondary are both slightly more exposed. And their difference compared to their partner is about the same amount. More to follow.

    And yes.....it is part of the fun.
    FFR MK4 Complete Kit #8952
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  34. #34
    Senior Member srobinsonx2's Avatar
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    T Slot update

    I talked to tech line at Quick Fuel today. They were very helpful and cleared up a few things.

    1. The primary side T Slots should be even. Mine are not and more on this below.
    2. The secondary T slots are suppose to be slightly different. The passenger side T slot on my secondaries appears to be 0.02-0.04 inches lower than the driver side when compared to the butterflies. Quick Fuel confirmed that is about right and is by design.

    Since the primaries T slots should be identical in relationship to the butterflies, I was concerned. I have a dual plane intake and was concerned about different air to fuel ratios across the cylinders. I shared the amount of difference I am seeing and the tech guy said I should be fine and did not recommend any special adjustments or purchasing a new carb. He did say that I could use an open phenolic spacer insted of the ported or 4 hole version I currently have. He said this would help communicate the vacuum, or "signal" as he called it, from both banks to both primary barrels. This made sense.

    So long story short is, the Quick Fuel guy says I am ok and should not worry. I tend to trust him since he would profit by erring on the cautious side and saying I need a new carb.

    I thought other might be interested in my finding. I will plug along and hopefully do some tuning this week, if it will stop raining. Since I am stuck inside this evening, I will try and load the LM-2 software and do some calibration. I will update you guys on how that goes.
    FFR MK4 Complete Kit #8952
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  35. #35
    bobl's Avatar
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    Give me a shout if you run into any questions with that LM2. I've spent a lot of "quality" time with them.

    Bob
    Mk IV Roadster, 347/516 HP, 8 stack injection, Holley HP ECU, Astro Performance T5, 3-Link 4.10 gears, A/C, PS, PB Purchased 08/2015, Graduated 02/2017

  36. #36
    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by bobl View Post
    Give me a shout if you run into any questions with that LM2. I've spent a lot of "quality" time with them.

    Bob
    Thanks Bob. I will give you a call later today. It appears I have some software issues. The handheld works fine but am not having much success with importing logs to logworks or connecting the handheld to check the firmware.
    FFR MK4 Complete Kit #8952
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  37. #37
    Senior Member Avalanche325's Avatar
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    I have to say that I REALLY don't like the answers that you got.

    Throw an open spacer on to fix the primaries......really? There is a problem that needs to be fixed, not put a Band-Aid on it. I would actually be fixing it myself. First I would check the base plate for warpage. If it is good, I would do some tweaking.

    This is my fist QF carb, so maybe I am wrong. For the secondary's, It has been a while, but I don't remember mine being different. All of the tuning books, threads, and videos that I have seen give one measurement. I have never seen one that said, "this much on the driver side and that much on the passenger side." Until one of our resident gurus says different, I am doubting this.

    Yes it will run with those suggestions, but it will likely never be right.
    Last edited by Avalanche325; 09-27-2017 at 06:13 PM.

  38. #38
    Senior Member srobinsonx2's Avatar
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    Quote Originally Posted by Avalanche325 View Post
    I have to say that I REALLY don't like the answers that you got.

    Throw an open spacer on to fix the primaries......really? There is a problem that needs to be fixed, not put a Band-Aid on it. I would actually be fixing it myself. First I would check the base plate for warpage. If it is good, I would do some tweaking.

    This is my fist QF carb, so maybe I am wrong. For the secondary's, It has been a while, but I don't remember mine being different. All of the tuning books, threads, and videos that I have seen give one measurement. I have never seen one that said, "this much on the driver side and that much on the passenger side." Until one of our resident gurus says different, I am doubting this.

    Yes it will run with those suggestions, but it will likely never be right.
    Avalanche325,

    Thanks. I appreciate the honest feedback. I wasn't real excited at first but the guy was pretty adamant that it would be ok. I fretted over his response all last night and came to this conclusion. I don't think it will hurt too much to give my current carb a try. If I can't get it lined out, I can always pick up a new carb. Do you see any real danger in this approach? You input is appreciated.

    I will take the carb off and check the baseplate for warping. When you say "tweaking" what do you have in mind?
    FFR MK4 Complete Kit #8952
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    3 Link Rear Suspension, Gordon Levy 347 SBF with T5
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  39. #39
    Senior Member srobinsonx2's Avatar
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    LM-2 Update

    Made some progress on the LM-2. Got the software installed without issue. I have only issue yet to resolve. I can't get the LM-2 handheld to connect to my computer. I keep getting a USB device error. It is either a bad driver or bad hardware (something with the LM-2 as I checked the cable and USB port on my computer). This ins't a show stopper since I won't be using the LM Programming software. Here are some other learnings so far:

    The system is easy to turn on/calibrate and I got the wideband O2 sensor up and running right away (via power in my daily driver). When doing this calibrations I just held the O2 sensor in my hand, let it warm up and then calibrated. When done the O2 sensor reads 20.9. This is not an air fuel ratio but is the oxygen concentration in air. Any AFR above 100, the handheld displays and records the concentration of oxygen and not a true AFR. This can be recorded as such and played back on the handheld. When the log is imported into Logworks 3, the software can only display AFR's between 7.35 and 22.38. Anything above or below this range, the software trends will only display the max or min and not the same value as the display (in my case something near 20.9).

    An SD card reader works great to import the logs and pretty cheap.

    I got the analog cable hooked up to the tach to measure RPM. Since I am using an MSD ignition box, this system requires I connect to that wire. On my MSD-6AL the tach signal is a gray wire. Found it and made a tie if for it and a ground. Also ran the wire for the O2 sensor and got it installed in the exhaust. I tried to power this all up but ran into an issue. On my car, I installed a USB power supply for charging my phone. The LM-2 has a cigarette lighter plug for power. I bought a USB to cigarette lighter adapter off amazon for a few bucks. It would power up the unit but apparently won't provide enough power to warm up and run the O2 sensor. To verify, I checked this USB to cigarette lighter system in my daily driver and had the same issue. The LM-2 and sensor works great in the daily driver when connected directly to the cigarette lighter. So I am going to pick up a cigarette lighter power outlet tomorrow and replace my USB power outlet. Should be easy and that will allow me to get my tuning system up and running.

    I am very hopeful that the LM-2 system will provide good data and allow me to properly tune my carb. But be aware that it appears the LM-2 does have a learning curve and a few idiosyncrasies that one must navigate to use the system proficiently.
    FFR MK4 Complete Kit #8952
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    3 Link Rear Suspension, Gordon Levy 347 SBF with T5
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  40. #40
    Senior Member Gordon Levy's Avatar
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    FYI, I have found 1/2" open spacer on that really helps the upper mid range and top end
    99/2000 NASA PSO Champion-2005 west coast FFR challenge series Champions
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