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Discussion Starter · #1 ·
Hello guys I apologize for a new post but I did not want to post on an older post as I am getting ready to try some tuning this week once it gets warmer out and I have been thinking on some things and thought of an idea on something I could try and a few other things but I don't know if it would help or not but its something I have never thought of before on a Holley with a 2 corner idle adjustment circuit.

This is a mild 350 Dart shp build with 200cc dart pro 1 platinum aluminum heads with an Edelbrock performer rpm intake with a 268/272 220/[email protected] 510/510 lift 110/114 lsa, and will be using a once inch open spacer and will be trying a 4 hole tapered spacer and a 4 hole spacer.My current open one inch spacer was only used temporarily until I got my intake sealed finally and warmer weather to be able to work on things. Timing is good at 12 to 16 initial with vacuum advance adding 12 to 14 degrees at idle for close to 30 degrees combined at idle on full manifold and 17 inches of vacuum in park with 800 rpm idle.

Some on here might already know some of the things I have been through over the last year.I am using a Holley 600 vacuum secondary 80457 with an added secondary metering block upgrade and I also installed down leg stepped boosters in place of the straight leg boosters. I currently have stock idle feed restrictors size in the metering blocks of .028 primary and .031 rear and its been tapped for brass allen set screws which is out of the box specs that the carb comes with. I have only tapped the secondary metering block as it came from a previous carb I used and already modified it. I have not done the first one yet.

I know on my idle circuit there is a possible lean spot when letting of the throttle as the throttle snaps close it will sputter for a second or so then smooth out.

Holding the idle in park between 1500 to 1900 rpm it seems to sputter holding it steady.In park it will sputter as well but in gear it will smooth out just fine. It seems in certain spots on the idle circuit it has some spots slightly too rich and others maybe to lean.

I never had these two symptoms at the same time on the idle circuit before. All other areas it runs well and snaps good in park and also while taking off and steady cruise at highway speeds. My thought was I know previously trying to use .031 primary idle feed restrictors front and back seemed to be too much but that was with some other issues so I don't know how it would respond again with finding out about the previous carb and the base plate being a big issue I had.

Ok on to a few things I was trying to think about and wonder about your opinions if the few things I am thinking of would make much of a difference in any effect or not. The first thing I was thinking about is when using a regular dual plane they normally say to keep the runners separate which I understand and by using a tapered spacer it will not do that but I am going to try and see how it works with things.

But the thing I was thinking about is if I don't use the tapered spacer and use the 4 hole spacer. If I used the open base gasket like all the Holley carbs come with it will leave a 1/16th inch of a gap between the spacer and also the carburetor itself on both spots and will allow a tiny amount of both sides being able to feed from each other. Would that be enough to cause any negative effect on things as can come up in certain instances on dual plane intakes such as when overlap occurs and exhaust reversion?

I have normally in the past always used a 4 hole gasket with a 4 hole spacer on top and bottom but I have a ton of open gaskets from rebuild kits used over the years and just wondered if it would cause any change of fuel falling out of suspension between those two very minor spaces?

Reason I ask is one time last year taking off my carb from a 4 hole spacer using the open base gasket I saw where it looked like fuel was puddled on the spacer in the middle.

The other thing I was thinking of was the idle feed restrictors. I know on a four corner idle they are normally equal sized front and back and are separate from front and rear. On the two corner idle setup the front and rear share each other in the track on the base plate and the rear is fixed with the idle discharge port and also an added tiny hole but don't know what size it is.

The primary side is where the adjustment takes place and I was thinking if my idle circuit needs to be enrichened up just a hair I was thinking would it make any change if I were to make the front idle feed restrictor size to .031 and then went down in the rear to .028 wold that make that much of a change since I can adjust more in the front versus in the rear its always just fixed and can't be adjusted outside of changing the ifr size and rear idle air bleeds.

I know it won't take too much of a change to get where I need to be but I never thought of that before as making the primary side slightly more rich and then leaning out the secondary side just a hair would it allow a slight enough change to possible just get it enough without being to much out? I know its always a trial and test type of a deal but was just curious on it that would do anything before tying it?

Several reasons I am using a spacer and won't be getting rid of it but will be tuning to run with it. I like using the 4 hole the best for street driving and won't know yet the effect it will happen since finding out my last problem with previous carb setup. Was just a few things I was thinking about and never really thought about before. The reason I ask about the gaskets is I found this and it was interesting but I know results will vary.


Thanks guys on any opinions.
 

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The primary side is where the adjustment takes place and I was thinking if my idle circuit needs to be enrichened up just a hair I was thinking would it make any change if I were to make the front idle feed restrictor size to .031 and then went down in the rear to .028 wold that make that much of a change since I can adjust more in the front versus in the rear its always just fixed and can't be adjusted outside of changing the ifr size and rear idle air bleeds.

On a 2 corner carb the idle screws in the front also control the base plate passages. So I’d assume some benefit is passed to the rears. IMHO the .031“ is a bit large. The .029“ (balance between the two sides) on all would be my start. On OEM carbs of the 60‘s the rears were same or smaller. I could never understand why one side needed more than the other on the idle circuit.

I make a habit of closing off the constant feed (.022”) ports. Stale gas is not a concern. Maybe that’s why my results are all same size IFR’s. Not saying this will work on all combo’s, but have worked out nice for me. Understand I don’t have any carburation training. All trial and error.

Keep us posted on any new findings or changes.
 

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Discussion Starter · #3 ·
Don't worry 57Nomad I will keep what I get just in case in the future anybody would come across my post and pick up some information that might help them. I plan on tomorrow swapping out my spacer and then seeing what it does and how it reacts and also will be driving it come Wednesday and Thursday and I already got some idle feed restrictors made in different sizes and will try a few things like I mentioned above.

I have a different primary metering block I bought from allcarbs and its an aluminum Quick fuel style block that has the changeable idle feed restrictors and stuff and the three emulsion ports versus the Holley two ports. I could have drilled out the primary metering Holley block but I just want to get this thing working and am tired of doing so many things in trying to get the last few wrinkles worked out on it. This is a first time where it seems to be lean on some spots and rich in other spots just on the idle circuit.

I have had where it was just either a little to rich or just to lean before but not both at the same time on the idle circuit. This has been the most picky camshaft I have ever had to tune with I must say. I had an easier time with an old 350 running a comp cam big mother thumper hydraulic roller cam which specs 299/319 243/[email protected] 531/517 lift 107 lsa. I used a two corner idle Proform 650 double pumper carburetor and only took me two days and it was on a Edelbrock RPM air gap intake with a 4 hole one inch spacer and took some tweeks on the ifr sizes just on the front but the rears were never a problem.

I ended up with the idle mixture screws out at 1 3/4 of a turn both sides and a 1100 rpm idle and correct transfer slot exposure and no rear transfer slot needed showing and also had clean plugs and never any signs of pig rich condtions and it ran as good as what you can expect with a cam that big on the street. It never fouled out my plugs or made them black but that cam was just not street friendly and did not live up to the hype and hated it compared to previous builds.

I don't know why I am having such a hard time with my current cam which is so mild compared to other ones I have had in the past and should not be this hair pulling. I am almost bald lol if I were to literally pull my hair out. I am sure that I will figure this out and it might just have to take some new trial and errors outside of the normal tuning box.
 

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Discussion Starter · #4 ·
Hello guys I was wondering is this normal to have fuel left over in the intake runners like this? The spots were there is nothing is where I wiped it away with my fingers and it was not like fresh fuel that was in there but was more like kind of a tacky feel to it. I have not driven my truck in a week and a half and I do not have a leaking carb a I have already checked over everything on it and the carb still had fuel in the bowls and it was dry. I know it can't be any flooding problems as my fuel pressure is good and I have checked it while running and shutting it off and never anything dripping from the boosters or fuel bowl vents. The bottom of the carb was dry and I did not spill any fuel while taking it off and changing out my spacer. The last time I ran it was on a 67 degree day.
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Eric, I’ve seen this when the fuel drips when the engine is turned off and let set a while. My source of the drip was the venturi. Seems the secondary air bleeds were not doing their job as a fuel break, I thought. Cleaned them out and was still doing it. Replaced the secondary meter plate with meter block conversion an it stopped. I don’t understand it as there is only passages in the meter plate. None of them were obstructed. Since the conversion to meter block fixed it, I didn’t pursue it any longer. My only thought is it didn’t seal against the main body as it should. It was warped about .010” and even after making it flat again…..same thing….. it dripped.
 

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Discussion Starter · #6 ·
Well this has been with two different carbs with three different main bodies and two base plates. I have no signs of any fuel dripping out while I shut it off and definitely no fuel boiling problems as it would have not been warm enough out. I have checked it while it was running and shut off and has always been dry in the barrels even hours after checking.

When I had my carb off I angled it forward and back and I had fuel come out the boosters so I know my fuel bowls were full and not leaking internally and I know my power valve is good and tight and not leaking or blown. The whole intake runners was like this and coated on all eight of them as far back as I could see so I don't think fuel is just dripping out and then coating my runner like that is it was the same all over inside and even when I had my intake off to reseal it again I looked into my cylinder head intake ports and they were the same.
 

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Must be occurring while engine running. Fuel rich and dropping out and collecting on the manifold. I’m thinking it has to be fuel from your description. See how the “grid” pattern is on the floor. GM aluminum intakes do not have that they are smooth. Fuel when it stains does produce that goldfish color. Same on exterior of manifold if there is a leak and not wiped off right a way. But I’ve never seen it collect as to be “sticky”.

Might you have some kind of additive in your fuel causing this?
 

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That looks like the anti friction additives the pipline add to ease pumping oil down the pipelines or possibly traces of Ethanol. It's nothing to worry about.
 

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Discussion Starter · #9 ·
Thanks Johnsongrass1 and 57Nomad. All the fuel in my area is E10 so I just did not know for sure. Its been so long since I paid attention to little things like that. The tacky part could be because of the pcv valve taking in crankcase gases as it is hooked up to the rear of the carb and I known that oil film after being heated would be like a tacky feel to it.

I have good baffles in my covers but I still get some oil film but hardly anything to cause any issues.
 

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Fuels do get contaminated with other things in transit. Pipelines are not generally one product shippers. They run different liquids say gasoline and styrene monomer with at least in theory a water slug between them. All of this gets separated at the delivery end , at least in theory. When I lived in Houston back in the mid 1990’s there was in incident with heavy styrene contamination in the gasoline to where thousands of car engines were ruined. This happened again in Seattle a few years ago but not so hugely with fuel from the refinery in Anacortes. So I imagine that some low level of product contamination is always present, rather like rat turds in grain products that we eat, there is an agreed to level of contamination between pure food and drug law and the manufacturer’s of these products.

As for gasoline itself it is a pretty complicated chemical brew that by itself forms varnishes, gums and precipitates. Everybody these days get all excited about ethyl alcohol as a root cause to which I’d offer a weak “maybe”; but sticky, icky stuff left behind as fuels evaporate is nothing new and is a lot less to day than years ago

One can easily imagine that the waffle pattern at the bottom of the plenum catches and puddles fuel especially at idle when mixture velocity’s are low with poor mixing off the idle circuit, the directional change and gravity would favor pooling here. Then the liquid portion evaporates leaving varnish and gum behind.

So what you see has always been pretty common, it may change with fuel blends by season and geographic area, It might be the result of in-transit or storage contamination not having anything to do with the engine’s AFR.

Bogie
 

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Discussion Starter · #11 · (Edited)
Thanks Bogie I love your history lessons you always have to share on here.Well I had my truck out today and I rechecked my timing and corrected it since I had last had my intake resealed. I got my truck up and running and warmed up and messed with the idle mixture screws to see if any real changes on different areas of adjustment and seem to stay consistent until I start to get to half a turn out on one screw and it kills the engine in gear.

So as I had it running I checked my spark as it sounds like at times a cylinder misfires or drops and picks back up looking at my vacuum gauge which was a steady 16.5 after warmed up and you could tell as the engine would be smooth and then rough up a hair just very faintly then smooth out again. While this is happening I checked my plug wires on the distributor cap seeing if I had any change on any particular cylinder and it was ok all around so I don't think there is anything ignition related wise as all my plugs looked pretty good. The vacuum would drop a hair when it did that and pick back up and the needle was always steady and smooth.

So after I had it idle for a while and the engine was good and warm I then raised my idle up by closing my choke some but not full engagement but just a hair to have it about half open and half closed and it seemed to smooth out my idle and the engine was smoother. I then opened it back up and I then would place my fingers over the back rear idle air bleeds for a few seconds and my vacuum would drop to 15 inches but my engine smoothed out and take a bit then would want to quit a it would make it super fat if I left it like that.

I did the same with the front idle air bleeds and the engine would be less shaky and smoothed out like it was watered down some and the vacuum dropped some but the engine did not stall right off and after about a second and a half then letting my fingers off it would catch back up. With the 4 hole tapered spacer I have picked up some throttle response over the open spacer which is a given considered the open spacer if for top end and more plenum volume and would take signal away on the bottom end.

Its not a night and day difference but you can tell a change. I took it out for a drive and just in town below 35 mph as that is where all the stuff is at with the problems and I still have the sputter when letting off the throttle as the rpms slow down from 1500 and below for about a second or so depending on conditions and throttle angle and speed.I know that the PCV valve adds vacuum to the carb and leans out the mixture some so just for fun I unhooked it and see how it would drive and in all honestly it actually drove slightly worse and did not have as much response with it hooked up.

I just wanted to see if it would show any sings that the idle circuit is too lean. Now while I had the PCV valve unhooked and I went to hook it back up and I was not quick enough it killed my engine instantly that the air got sucked though the hose before I hooked it back up.

Now from what I am seeing in the idle circuit its to lean at certain spots but idle is smooth for the most part and throttle is snappy and smooth when it is hit fast or slow in any gear and takes off like a rocket with no issues. So basically I have that off idle sputter when letting off the throttle and also some slight sputtering when holding the throttle steady.

Now I can take off the tapered spacer and install the 4 hole spacer which should enhance the signal even more and wonder if it would be enough just to change the air fuel ratio enough to get rid of it or not. I know the full open spacer on my previous issue with previous carb it would make it run richer versus the open spacer and the tapered spacer I never used on it.

So my assumption is the tapred spacer takes away some of the leanness and slightly enrichens the air fuel ratio compared to the open spacer since there is less cross flow between runners and more velocity and better signal to the carb. I don't know what to do with my carb wise as I don't want to make it to rich on the idle circuit and want to keep it as lean as possible without being to lean.

I currently have .028 primary and .031 secondary on the idle feed restrictors and I have bleeds and stuff to use but I wish I could go to a .030 only on the front instead of .031 but my drill bit gauge set only has .028 then .029 and jumps up to .031. I was wondering what effect would it be if I changed the front to .031 and put the rear at .028 and would that allow just enough of a difference in setting to maybe give it more adjustment and a slight enough change to see if it would get rid of it since I can adjust the primary side but not the rear as its fixed.

I could go up primary to .031 and leave the rear at .031 but I would like to try to keep it as lean as possible without having it be more rich versus lean. On previous carb it would not run like that but I guess all settings on it would be thrown out the window since I had no adjustment on the mixture screws like this one.

Now the curious part that has me puzzled is on the last problem I had with the previous carb which through the base plate causing it to be so fat rich on the idle circuit it would still have that sputter off idle even though it was fat at idle and fouled my plugs out. My spark plugs all looked pretty clean and some tan mostly with some faint blackish gray where it fired.

I never had a sputter when letting off the throttle before like this so a new one for me. If I get rid of the off idle sputter and the sputtering here and there problem then I am golden. I got about 90 percent of tuned. Just that small area.Thoughts?
 

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Why do you not want to “balance “ the idle feed restrictions. Split the difference and install all at .029”. It is not a diameter that determines the flow but the area.
.028” gives .00061area, .029” gives .00066 area, .031 gives .00075 area

You currently have a 19% difference between front and rear.
 

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Discussion Starter · #13 ·
57Nomad I understand where your coming from but with a two corner idle setup its kind of different then when using a four corner idle. You can't always have them the same and I don't have all the knowledge to get into things but if I were to put the rear from 31 down to .029 that would lean it out but while that might work on the secondary side and I still need to be richer on the primary side and going from .028 up to .029 might not work out and be enough as already its to lean from what it seems to be doing and I might end up having to go .031 front and leave the rear at .031. I have had many times in the past to where the front was not the same as the rear on the two corner idle setup and it was never a problem and ran good and clean.

I will put that down and give it a try just for the heck of it as I have nothing to loose at this point and will try just about anything that is out of the norm that I have not done in the past. I also will be sticking my 4 hole spacer on before changing anything to see how it does and have the two intake runner separated like a dual plane is supposed to be. The tapered spacer did pick things up some but by how much I don't know as I won't keep driving it with the sputter and I want to tune on the spacer I am going to use that gives me the best for street driving and the four hole is the best when bottom end and mid range are important. I only used the open hole temporary as it allowed me to run the truck long enough to get some things fixed on it until I could go back to figuring out the tune and problem that has plagued me for a year plus.

Now that I got a working carb again I am in the ballpark and I am very close and once I get rid of the sputter on the idle circuit and the few tiny blips here and there at low speed then I am golden. Highway it runs like a charm on the main circuit.

I got me a Transdapt Swirl torque spacer on the way as its supposed to help create a vortex and help with air and fuel atomization and I used one many years ago and it worked awesome for me on a mild build similar to this and would have gotten one sooner had I known they still made them. I don't know what happened to mine and most likely it went with an older motor I sold. I will keep your idea down and go with that after my spacer comes. Thanks again for your input. Always appreciated.
 

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Yes, 4 hole spacer should improve over the open one. I’ve no knowledge of the transdapt swirl torque space so can’t say yea or ney. I’d be interested to hear how well it performs. Keep in mind carburetor base plate track grooves from front to rear is only part of the feed to secondaries idle. The rear IFR orifaces feed too. This is why on OEM stuff the secondary idle air bleeds are smaller on the secondaries on 2 corner carburetors to keep signal stronger.
 

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Discussion Starter · #15 ·
Yeah 57Nomad I know about the base plate tracks to where on the two corner idle will share with the front side as to where the four corner idle base plates don't have that. I have even built a two corner idle holley carb over to a four corner idle carb once so I know all the ins and outs of those as I have worked with them so long and on many different builds.
 

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Discussion Starter · #17 ·
49 Ford Coupe I can understand where your coming from as there was a time I quit using Holley carbs for other reasons but that was before I really got to know them and tune with them and learned to know how to really adjust and tune them with more then changing jets and turning screws.

Its just my preference and my go to choice and weighing the pros and cons with running what carburetor I use. The Edelbcock AVS2 would be the other choice for a secondary carb to run.
 

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There is also others that are still a Holley design that have more features, changeable brass orifaces, dual sight plugs, billet meter blocks, aluminum construction vs the older pot metal.

But understand most (Quick Fuel, Holley, FST, Summit, etc) do not come tuned out of the box even close to what you many need for the engine one is going to install it on. So yes a bit more difficult and time consuming to tune but a better fit can be achieved. This does assume one puts in the effort to learn and tune to get the results. If one is not inclined to do so a Q-jet or Carter AFB or WCFB or as mentioned by Eric the Edelbrock would be a better choice. Understand these are generally lesser flowing carburetors and not give the performance one wants on a built engine. And assuming you look and can locate a NOS 60’s OEM muscle car Holley or Carter that might be a good option.
 

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I know nothing much about holley carb tuning but read this thread with interest. My gut reaction is you are way down a rabbit hole and may be overlooking something. First thing I would do is a compression check. Are all the cylinders even? If nothing else as a base line for the future. I would also get a wide band O2 sensor to see what is actually taking place. I have a 240 6 with a 500 eddy carb and installed one on my dash. Quite an eye opener. The carb came with a 5" spring on the metering rods and I had a hesitation upon acceleration. I first thought it was because of no heat riser under the intake manifold. It did not bother me but the O2 sensor said it was going lean. I changed the spring to the 7" spring and it went away. Engine runs great no stumble. BTW idle vacuum is 15".

My point is there are tools available to help you. Yes the O2 sensor is not cheap but neither is all the parts you are buying for the carb and your time. There are portable hand held sensors. Just get one that has good reviews, not the cheapest.
I admire your persistence. This is why we are hot rodders!
 

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Discussion Starter · #20 ·
I agree that a o2 ratio gauge would help with things and I have a dual exhaust and I would not know where to start as far as that goes in getting a gauge and hooking it up wise. My headers don't have the provision for an o2 sensor. Regardless I have done a compression check on the cylinders I can get to and they are all the same at 160 psi. I have exhausted everything else and it would have to be carb related as the previous carb I used for some reason the transfer slot length in the base plate was my my first problem.

It took me a while to figure it out and find that issue but now I just have this other issue and will try to get it to be gone. I have used experience and knowledge and old school methods to tune my Holley carbs over the last 13 years and I have always gotten to where I need to be with all of them. This is just one of those occasions that a curve ball has been thrown at me and I need to really dig in things to get to where my engine needs to be. I believe I can get this but it will take some trial and error deal and that goes even with using an o2 gauge which would be helpful and if I become desperate I would consider it. Have been wanting to for years but have never gotten around to it but maybe this is the time to do so. Thing is I don't have a welder and don't know how to weld a bung in place etc.
 
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