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  1. #1

    Default Trying to dial in my 1806 Carb

    Looking for some feedback and advice on setting up my Edelbrock 1806 thunder. I am certainly not a carb tuning expert and I know there are very knowledgeable people on this forum with these things. I have however wanted to get into this for a while and learn in the process.

    So last year I splurged and got an Innovate dual wideband O2 in order to help dialing in my carb (and possible others) for a happy medium between economy/performance.

    I did some reading up on AFR's and tuning and have played around and experimented with a few things etc. Came to the conclusion that the 1806 stock calibration out of the box was quite rich overall everywhere which was kind of expected from what I read. Anyway I ended up just changing metering rods to a 1452 (2 stages leaner on cruise and power from stock) keeping the 1426 jet and that certainly leaned things up as expected. The fuel I'm running is your normal lower grade E10 mixture which should have a stoich of 14.1 or so from what I read.

    After some playing with the mixture screws this is what I'm seeing now for AFR's:

    Engine seems to like the idle mixture set around 13-13.5. Just off idle drops to 12 or so (accel pump rich ?). Light to steady cruise when driving is around 13.5-14.5 now (perfect ?). However if I lightly step on the gas its leans up to about 16 or 16.5 briefly (too lean ?), a little more gas and it will return to the 14's or so. If I go up a slight hill same thing. If I punch it the AFR will drop to low 12's so I think that's still a bit rich. This changes a bit depending on what gear I'm in etc.

    I find leaning or richening the idle AFR will also affect the cruise proportionately. Probably mainly cruising/driving on idle circuit from what I understand.

    So my main question/concern for the moment is if hitting AFR's of 16 or 16.5 briefly during these cruise conditions is running too lean ? The car doesn't seem to hesitate or anything and it does richen up with some more pedal. I pulled my plugs after a fairly long drive and they were tan to slightly grey now which kind of confirms the leaner AFR readings in my opinion. I'm not too keen on melting pistons LOL

    Any comments/suggestions are welcome.

    Thanks in advance

  2. #2
    FEP Super Member cb84capri's Avatar
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    I haven't messed around with an AVS, but from what I understand they are the same as AFB but can have the secondary air valve timing tweaked more easily. So with that in mind, I would suggest trying the silver step up springs next. This will speed up the transition as it will allow the rods to shoot up at a higher vacuum level. Don't worry about the momentary rich dip when throttle is applied, it is a necessary blanket of fuel needed from the accelerator pump as the carb transitions circuits. 12:1 isn't bad momentarily.

    With the engine unloaded, you shouldn't hurt anything running on the lean side of 14.7 unless it is catted. When it's in power mode and you're really filling and pressurizing the cylinders is when you'll do damage. I prefer mid 12s at wot because the fuel distribution varies from 1,4,5,8 and 2,3,6,7 to be safe on the leaner outer cylinders. Port efi guys like to go 12.9-13.1 because they have better distribution.

    Honestly it sounds like you are pretty close to where you want to be to me. I have a thread with charts and stuff on here I did years ago when I was playing with my 600 and 750 if photobucket still allows it to be viewed.

    Cale

  3. #3

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    Thanks Cale

    Yes I am sure I read up on some of your thread on the 1406 when I was doing some research.

    Yeah I'm thinking its pretty good overall. Did another long drive tonight and tried different things. There were no real noticeable driveability issues other than now I'm fretting about where the AFR's are going on the fancy new guage (which is very cool btw) and trying not to hit the ditch haha.

    This lean spot is there at part throttle acceleration through all the gears but never goes above 16 for long and drops back down once I get past it. I was reading up some more and thinking about the step up springs. This certainly may be what I need to transition to power earlier so I will try the heaviest spring and see what happens. Good thing I thought ahead and ordered the kit. Usually I make a discovery and have to wait a week for parts

    I'm also going to pull the top off and try reducing the secondary jets one size leaner because the AFR seems to be dropping to 12 or mid 11's fairly consistently in a variety of WOT conditions to the point where I think it may be bogging down somewhat. I'm not sure how exactly this air flapper works yet and perhaps should be adjusted to open earlier on WOT ?

    I am also going to rig up a temporary vacuum guage inside the car to reference. That should be interesting to watch as well. I'm hoping that leaning everything out will help the fuel economy a bit too.

  4. #4

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    Forgot to mention I am running the magnaflow high flow cats in my exhaust. Do you think they might crater if I'm cruising a bit lean etc ?

  5. #5
    FEP Super Member erratic50's Avatar
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    One thing to consider when you are seeing lean conditions - what’s the base timing at and what are you seeing for timing advance? How many RPM are you at? You might be advancing too fast for the fuel present.

    Are you seeing symptoms of the lean condition or is it so subtle that it takes a gauge to detect it?

    It does sound like A/F is getting in the ballpark of where it should be. At WOT I wouldn’t worry too much about seeing a 12 A/F - there’s good power to be had there without hurting anything. It may like 12.5 a little more but knowing it varies I wouldn’t look to lean it up at WOT much more.

  6. #6

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    I'm running a stock duraspark distributor with some of the Mr gasket lighter springs installed and using a GM 5 pin HEI ignition module. Its set at 12 or so initial with a 20 deg curve so around 32 total all in by 2500-3000 if I remember right. According to everything I read this should be a pretty good curve for a light car. The vacuum advance can is hooked up direct to ported vacuum but i'm not really sure what its adding etc. I suspect it works because I see the timing jump around when giving it a quick rev from idle etc.

    Its a stock HO roller cam so has lots of vacuum (19 or 20") at idle which I think may be a contributor to needing a higher step up spring.

    Its possible I guess that the timing is too fast ? Would it be beneficial to use a vacuum delay valve possibly ?

    There are no symptoms of pinging, stumbling, or hesitating at that lean point other than the guage reading. Car does respond nicely in this llean spot if I give it some more pedal etc. If I didn't have the guage I wouldn't have a clue where anything was at...at all...LOL. I do trust the readings from the guage are correct though. I pulled the plugs and they are definitely not showing rich in my opinion but then again I'm no expert on that either. They are all relatively clean slightly tan and grey and identical from every cylinder. My concern is I was leaning out but maybe its not all that bad at these conditions etc.

    I do notice the AFR at idle is way more sensitive to the idle mixture screw settings than I expected. Doesn't take much to tweak it a point either way.

    Anyway I got my vacuum guage rigged up, installed the highest step up springs, and also went one size smaller secondary jets to try out. Hopefully going for a drive tonight to see what readings I get.

  7. #7
    FEP Super Member erratic50's Avatar
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    Glad you’re making progress

    Advance needs to be hooked up to a port that shows no real vacuum at idle and full vacuum at WOT.

    All in by 2500 often isn’t great with an HO cam frequently AFAIK. There are others who have played with this stuff a lot more though. for sure give it what it wants.

    if anything I’m guilty of being too aggressive with advance usually, but I haven’t played with a carb much in a long time. The last time I’ve messed with one was nearly two decades ago and it was a Quadrajunk my dad had worked over years before on a Buick 350 that just needed a basic rebuild and was dead nuts just being left how he had it once the crap was cleaned out of it. Never a dull moment with some of the hotrods he helped put together. Good fasteners and mostly stock parts, it was turning past 8500 and valve floating when it finally let go.

    I’m thinking moving the vacuum line will probably eliminate the A/F lean out you are seeing.

  8. #8

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    Thanks Erratic.

    Maybe I misunderstood but I always thought that the "ported" vacuum connection off the carb was none at idle (no advance), increasing advance at part throttle, and then at some point back to no advance again at WOT (where you get centrifugal advance timing only again)

    However I am no expert on this either. Would be nice to confirm. Maybe I'm on the wrong port ?

    I'm curious to see what the manifold vacuum guage tells me under driving conditions.

  9. #9
    FEP Super Member cb84capri's Avatar
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    You want to be hooked up to the small port on the front of the carburetor that is higher up. This is the spark port, and it is only exposed to see vacuum when the throttle blades open up and expose it. Vacuum is only supposed to be applied to the vacuum advance canister during part throttle cruising. What heads and intake are on this engine? Have you verified the slot width in your distributor?

    Briefly going lean shouldn't hurt anything, it's prolonged driving lean at those afrs that will nuke the cats. I think with just the metering springs you should be pretty good. The secondary jets make very small changes in wot afr only. To tune mine I would rap the engine out to 6k in third and keep an eye on the wideband. At the top of the rpm is where it leans out the most.

    Also the next time you have the top off of your carb, check the float levels. My 1406 which I bought new was not set very well from the factory.

    What main jets are in your carb right now, what secondary jets? 1452 rods still right?

    Cale
    Last edited by cb84capri; 05-02-2020 at 11:10 PM.

  10. #10

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    Yeah the engine is a bit of a long story going back some years. A weird combo of parts for now that we threw together and will put in my sons car eventually.

    Its a 30 over stock non-roller block with retro tie bar lifters. Edelbrock F4B intake, Keith black hyper pistons around 9.5 compression. Aluminum heads 2.02 valve setup with roller springs/1.6 roller rockers....and all with a stock 95 HO roller cam. Now I know what your thinking...WTF right...but its what we had and this engine is going to be a more regular driver so wanted manners and thought we'd try it. I can say overall though its really not too shabby going through the gears.

    Yes right now it has 1426 primary jets, 1452 rods, silver springs, 1426 secondary jet

    I took it out and beat on it a bit more tonight. The vacuum guage tells me exactly. The lean spot is happening just before the step up springs kick in to power mode. Right on cue it richens up to AFR 13 around 10"hg and less with the silver springs. This tells me the power mode rod size is pretty good too. Its a bit better now than before but still there in all the gears if you are slowly increasing the throttle.

    So what I need it would seem is about a 12" step up spring but they don't make one it would appear...or maybe I need a more radical cam to get the vacuum down or maybe this is why they invented EFI LOL. Overall though I don't think that is that much of a problem either. Normal driving its fluctuating up and down, always at very small throttle, and never stays there consistently etc and I don't notice it driving wise.

    As for WOT its hard to tell but the seat of the pants tells me the smaller jet (from 1427 stock to 1426) in the secondary seems to respond better but the AFR is still hitting low 11's fairly consistently. I think it may still be a bit too big. Before I change it again I will wind it out a few times and pay more attention to it again. Realistically its not going to see WOT all the time normally anyway.

    Oh well I'm learning lots anyway and it seems the mileage has improved too despite all the WOT

  11. #11

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    Oh yeah forgot to mention I did verify the advance slot in the distributor a while back when I researched how to set it up. Cant remember the exact number on it but I did verify that it stopped at about a 20 deg or so advance maximum from initial without the vacuum can hooked up at all (all centrifugal). I'm confident the timing curve is decent and I'm on the upper ported vacuum signal.

  12. #12

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    This is what all my plugs look like after a few hundred miles on this tuning combo idling as little as possible. What do you think ? They were also blackened a bit before this from idling a bunch without driving in the winter. I could throw in a brand new set to get a new read too.

  13. #13
    FEP Super Member cb84capri's Avatar
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    It doesn't look like anything bad is going on, but to be honest I have little faith in my abilities to read plugs.

    The only other course of action I think you have at this point is to try increasing the accelerator pump stroke by moving the link to a hole closer to the lever pivot. If you go as close as possible and it still doesn't take care of it, you can then replace the accelerator pump squirter with a larger one or drill the nozzles to a larger size yourself. I have found with my 600 and 750 carbs on my car that as lean as I have mine tuned in cruise, I need all of the stroke and the biggest nozzles. Carbs do have their limitations. Do you have a link to the cylinder heads you are using?

    Cale

  14. #14

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    Yeah easy enough to change the pump linkage and stuff. Its in the middle hole now from stock. Actually these carbs are relatively easy to work on.

    I was even thinking about mashing two step up springs together (like they come in the package) to see if I get a somewhat higher rated spring. Know anyone who's ever tried this ?

    Like I said it seems I just need them to come on a bit earlier. Easy enough to try the spring idea, if anything I'm guessing they will be stronger and I will be rich very early or all the time. Some of the literature I read says cruising at 15-16 AFR is best for economy too so maybe its better to leave it alone.

    The aluminum heads are NKB-274 from skip white performance. I was a bit leery over the possible quality of them when we ordered but couldn't argue with the price for assembled heads so thought why not give them a try. So far so good but have't got many miles on them yet either.

    Thinking about the WOT perhaps it needs to be 2 stages leaner than stock as well for my combo (1425 jet) just like the cruise/power adjustment.

    For sure I really get it now that its pretty difficult (or maybe impossible) to make these carbs (or a carb) everything at every condition to every combo. The wideband certainly is a great tool to see whats going on though. I can't imagine not having direct feedback and throwing in rods and jets and tweaking relatively blind haha. Much easier for the rookie tuners !!

    Thanks for the advice.

  15. #15

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    Whoops I just re-read my posts and noticed I forgot to mention the engine is a 306 in case you didn't already guess

  16. #16
    FEP Super Member cb84capri's Avatar
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    Quote Originally Posted by at_the_junkyard View Post
    I can't imagine not having direct feedback and throwing in rods and jets and tweaking relatively blind haha. Much easier for the rookie tuners !!.
    The wideband is a real eye opener. I have tried to convey this message in the past on here and have surprisingly gotten quite a bit of resistance to it.

    I never thought of putting two springs together, I guess there's no harm in trying it. With the vacuum gauge hooked up it would probably be pretty easy to figure out where the transition happens.

    Cale

  17. #17

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    Yeah I don't regret getting the wideband but it was a bit of cost and work to install and get working which is a bit of a negative...but isn't that like everything we do on these cars !!

    Too bad I'm learning all this carb stuff about 25 years too late LOL!!

  18. #18

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    Well the two spring trick never worked. I tried two orange springs because I had 4 of them but ran rich 12's all the time. I think the fit interfered with the piston and it didn't move properly. Back to the silver springs and where I was before.

    I adjusted the secondary flapper valve to open sooner. The stock setting is 1 1/2 turns on the spring after close and I changed this to only about 3/4 turn. Seems better response. I tried WOT cruising at around 3K in third and wound it out to 6K. AFR went to about 11.5 initially and climbed up to 12.0 at the top end so its close and not leaning out at the top end. I'm tempted to try the 1425 jet in the secondary and do the same test.

    Once I'm done playing I will drive it normal and see how many miles I can get on a tank.

    I was researching parts and it appears you can get a spring kit for a quadrajet from carb parts supplier as below. Looks like the blue spring might do the trick for my combo. Just a matter if I want to pay around the $50 it will take to get them here.

    Overall though I'm pleased with the way the car runs now.


    You want to use the strongest spring possible that will NOT begin opening at idle.

    Spring / Inches of Vac. / Length
    Yellow: / (2-7) / 0.950"
    Silver: / (4-9) / 1.020"
    Black: / (5-9) / 0.950"
    Blue: / (8-12) / 1.450"


    Note:
    Inches of Vacuum are to be used for estimates only. Condition of power piston and bore can affect and change inches of vacuum. For example the blue spring is rated at (8"-12"), the power piston begins to open/lift at approximately 12" of manifold vacuum and is fully open/lifted at approximately 8" of manifold vacuum. For most stock engines with smooth idling camshafts will use the Blue spring.

  19. #19
    FEP Super Member cb84capri's Avatar
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    Good find on those springs! Do you have a part number for them, might try some myself. I used to live over there so I know all about that. Luckily I was close enough to Detroit, so I'd ship things to a UPS store and go get them myself.

    For future reference, the base calibration on the 1806 is:

    .095" primary jets (1426)
    .068" x .047" rods (1447)
    .098" secondary jets (1427)

    Currently you have

    .095" primary jets (1426)
    .070" x .052" rods (1452)
    .095" secondary jets (1426)

    Here are the spreadsheets I did years ago, I may load these to FEP so you can view them without the stupid pb watermark. These 2 below are the painfully accurate, hard on your eyes versions that show actual areas. They show a calculation of:

    Actual area of Jet - Metering rod step area





    Below are the 2 rougher, not as accurate versions that are easier to look at. They show:

    Jet size - Metering rod step size





    The secondary jets seem to make pretty small changes to my carbs WOT afr. I would try jumping another stage or 2 past that if 12.0 is the leanest it gets in power. Go with a .083" or .086", though the 1840 kit probably doesn't have them. I edited this post because I kept referencing these spreadsheets and thought it would be easier to have it right here.

    I want to show you an example so you can see how to use my spreadsheets, bare with me here...

    We can accomplish leaner power afr while maintaining your desired economy with main jet and metering rod changes still too. The Edelbrock chart you are looking at doesn't show you that. So the .070" step in the rod is working well with the .095" jet for cruise, you want to maintain that .025" difference on the rougher, not perfectly accurate, easier on the eyes spreadsheet. You can find the .025" in the smaller .092" jet size and it's .067" rod. Carb is too rich in power, so go from the .052" to .055" with the .092" jet to go from .043" to .037". That rod exists, it's 6755 part number 1463 rod. That's how my spreadsheets work. It isn't exactly the same in economy/cruise as you can see in the first 2 spreadsheets, but it's pretty close. I open Summit Racing's website and look at the available selection of metering rods like this:

    https://www.summitracing.com/search/...ibanner=SREPD5

    Cale
    Last edited by cb84capri; 05-05-2020 at 08:24 PM.

  20. #20
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    Make sure your fuel pressure is set to 5-5 1/2 psi max. These carbs a very sensitive to fuel pressure changes, and it will cause you to chase air fuel ratios. Because there are no site plugs in these carbs, you have to set float level with a gauge/ ruler, before putting the top of the carb back. Fuel level is very important in any carb, too high will cause fuel to come in too soon in all areas of carb operations, and the opposite effect if the fuel level is too low. Make sure you use a regulator and set the pressure first.

    Also the best afr for wot would be 13:1. No carbed engine will run cruise at 15-16:1 afr because of un-equal intake runner length, and un-equal fuel distribution to all cylinders. That's where port injection shines.

  21. #21

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    I found the springs at quadrajetparts.com. Part #3601 but you need to buy two sets. Pretty sure they will work in the edelbrock from the looks of them.

    https://quadrajetparts.com/quadrajet...ode-p-210.html

    Yeah thanks for the information on all the sizes. I think I read that effective orifice information on one of the threads here. I thought about different combos when it seemed that I might need metering rods that were in between what was available and what seemed logical to use next etc.

    I have considered that my power rod is perhaps a contributor to the richer AFR's at WOT. However when I encounter the 15-16 lean cruise spot at around 12" it is really at only maybe 20% or lower throttle position (guessing) and only takes a bit more pedal to reach 10" where you can see enrichment kick in drop AFR to 13 or so. I can see this in all gears pretty much if I roll through slowly but is really easy to see it in 4th or 5th with the vacuum guage. The car responds immediately though and does not hesitate during this transition so I kind of think the (52) size is decent.

    For example if I am cruising trying to keep a constant 60 mph speed on a slightly hilly road in fifth I am barely on the pedal (10%) on the flats, slightly more pedal (maybe 10% more) on the hill, and right off the pedal on the downslope etc. AFR will be around 14.5 on the flats, climb to high 15's or 16 on the slight hill, and then drop to high 13's on the downslope when backing off to the pedal to nothing etc. If the hill is large enough you need a bit more pedal as described and it richens up to 13's.

    So really this lean spot is only encountered temporarily most of the time but does occur. Not sure if that will really affect anything long term damage wise or not. If it wasn't for the guage I wouldn't know.

    All this leads me to believe I will probably need those $50 springs to cover that spot if so inclined LOL

    I have a set of 1425 jets Im going to try on the secondary and give the same WOT test. If it still doesn't cahnge much I'll consider getting an even smaller jet. I think the smaller 1426 has improved things already.

    Also I have not tried moving the accel pump yet either so will do some more experimenting.

    Cheers

  22. #22

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    Also I installed a regulator and set to 6 psi a while back after I read that in the manual and realized my pump was putting out 8.5 psi after I put a guage on it. I checked the floats and they seem to be very close to spec.

  23. #23

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    Another thing to mention I ran into was that setting the idle AFR richer/leaner also seems to have a fairly significant and proportional effect on my steady cruise AFR. This is tricky to get the right balance sometimes between what it wants to idle at and leaning up the cruise etc.

    For example I have found that when I'm light cruising my vacuum guage is only maybe 2 or 3 "Hg lower than idle vacuum, especially if the rpm is higher at a certain speed say between choosing 3rd and 4th or 4th and 5th gear etc. I guess it doesn't take much throttle to keep these relatively light cars cruising.

  24. #24

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    There's a wide misconception that "cruise", or even light part throttle acceleration, is the responsibility of a carburetor's main circuits. It just ain't so 95% of the time... an exception would be a very poorly geared car with very low power and having to have your foot half way or more to the floor all the time during "cruise" etc. Edelbrock's jets/rods/hangers/springs function is no different than Holley jets and a power valve, and it's all about the main circuits, the boosters flowing, much more throttle angle/airflow. Edelbrock jets and rods: vacuum holding rods down due to vacuum level = either transition still doing the fueling or greater than light part throttle acceleration and the main circuits flowing; after that, springs that reach/pass their design vacuum level allowing rods to travel up = full enrichment for WOT.

    Here's another misconception: "... No carbed engine will run cruise at 15-16:1 afr because of un-equal intake runner length, and un-equal fuel distribution to all cylinders. That's where port injection shines."
    Sure they will. I don't know how many times I've accomplished that for folks and for myself. I beg to differ, and will add that upwards of 17+:1 with additional light part throttle acceleration with a dialed-in carburetor is another supposed impossibility, that isn't impossible with some super-tuning. 100+ year old principals for carburetor calibration/tuning is still very much so valid today. Port injection's very forced, fixed, and non-adjustable nature dulls the supposed shine in short order.

    AFR gauges are a handy tool, most especially/importantly for monitoring WOT. If there's no protest (bucking/surging/"trailer-hitching") from the car at "cruise" or upon light part-throttle acceleration, both the responsibility of the idle/transition circuits, then the idle/transition circuits are fine, regardless of what the AFR gauge says, and can/should be modified to be leaner yet (upping primary idle air bleed size until there is protest, and then reduce primary idle air bleed size a few thou at a time until there isn't any protest, and then you're golden - you'll have found the very best on fuel the car will be for "cruise", and you'll enjoy super crispy part throttle acceleration like nobody seems to think is possible, clean plugs and oil, etc)

    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  25. #25

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    All good info...I'm into this now so going to experiment on this thing.

    Next move I think is to order up those springs and give the blue one a try. Its only money

    I am thinking though this may change the dynamic of the lean spot and possibly even the entire upper AFR curve to where my power rod setting may need to be even leaner perhaps. After that see where the WOT goes and work on the secondary jets if necessary.

    Its funny...I remember when I was 16 years old someone older told me that you needed to be 50+ and have grey hair to work on carbs. Well...this seems to be slowly coming true for me haha!!

    Thanks

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