nfhDODGEnfh
Well-Known Member
It floats around 12.2 on the afr gauge at WOT. I think.... can be hard to watch a gauge consistently when you have the foot on the floor hahaha
Nitrous on a 340 100 shot
- Thread starter nfhDODGEnfh
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nfhDODGEnfh
Well-Known Member
He has been a wealth of knowledge, support and parts that's for damn sure. Couldn't have gotten here without him
TT5.9mag
Two atmospheres are better than one
It can be. That’s about perfect for a n20 hit. And about what I’d expect looking at the fuel ring on your plug.
Inertia
Well-Known Member
Thnx for the kind words Mike, most of all that you did yourself .
Your a good listener, getting to be a great mechanic, good job .
Cheers
Ironracer
Gearhead
nfhDODGEnfh
Well-Known Member
Took the car out for another hit of nitrous today and snapped a pic of the fresh plugs that are one heat range cooler, and turned my timing back one more degree to 32* total and 12* idling. took the pics right after I gave it a nitrous hit to 3rd gear.
Cylinder #1 is the first 2 pics
Cylinder #3 is the 3rd and 4th pics
Then took another 2 pics of a plug after I got home from being stuck in traffic and idling a lot. Seems really dark and almost wet, even the porcelain is dark now. Does that mean my plugs are too cold? Or is it because my initial timing is so low? I could change my curve to a 15* sweep that gets total timing at 2500rpm so I would be 17-32 instead
TT5.9mag
Two atmospheres are better than one
The plugs look good after the nitrous hit. The first two pics look like you still have a degree of timing to take out. After driving it and sitting in traffic the plugs don’t look so great. Trim some idle fuel out of it. What afr are you idling at on your wideband?
nfhDODGEnfh
Well-Known Member
Trying to save fuel in high gear low rpm it was 11.7-12 ish..... it idles at 12.5-12.8 now that I pulled more timing out of the top but added 5 degrees on the bottom. Now I have it set to 16*-31* and I'll try that and see how it is wirh nitrous. While I was timing that in I idled it for 10 minutes ish and the plug looks a bit better.
nfhDODGEnfh
Well-Known Member
What is too low for an air fuel mix when idling? or driving in a high gear at low rpm in an attempt to save fuel?
Inertia
Well-Known Member
Mike, this would be a great place to look for that 8 1/4 side gear.
Perhaps put up a want ad .
Perhaps put up a want ad .
nfhDODGEnfh
Well-Known Member
Good idea and with Chris being in America on the westcoast maybe I'll get lucky finding an 8 1/4 sure grip or track lock. Also I might bring the car over this week if you wouldnt mind checking the tune on my carb now that I've messed with things a bit.
Ironracer
Gearhead
Y'all are Badass! I ain't set up a NOS system before, there's a lot to it other than forged slugs! My car is Pretty Darn Quick in 1st and 2nd, 3rd could use a 100 shot! Lol
TT5.9mag
Two atmospheres are better than one
You’re pretty safe at low load around 15:1. Cruise and idle.
TT5.9mag
Two atmospheres are better than one
You are still pig rich at 12.5-12.8 afr at idle. You need to trim some fuel out of it. The extra idle timing will help with the leaner mixture. And your plugs will clean up. This is when you get in to carb tuning that isn’t just mixture screws and jets. You might need idle feed or transfer slot restrictions to get enough fuel out at idle and still have enough in cruise.
TT5.9mag
Two atmospheres are better than one
@nfhDODGEnfh any updates? Have you emptied a bottle yet?
nfhDODGEnfh
Well-Known Member
Not yet, I've made 4 hits on it so far but it's been raining a bit here. I did just purchase some mickey thompson street slicks I need to put on next week because when I hit nitrous from first it just shredded the tires in first and secound gear. When I'm mounting the tires at inertia's shop I'll try to lean out the carb mixture aswell. I'll give and update again once I get the new shoes on too and give it a nitrous hit.
The carb seems to be pretty rich at idle and when I Rev it up too 3000 just on the primary's it's low 11's-10.9 and idles at 12.4...... I'm wondering if I should jet the whole primary side down a bit to correct that? since my wide open throttle is mid to high 12's. On wednesday next week me and Inertia will have a look at since he knows way more than me about carbs.
TT5.9mag
Two atmospheres are better than one
No leave the jetting alone. It won’t affect idle. You’re rich at idle and on the transfer slots. If you pull main jet out of it, you have to add it back in the power valve circuit to stay the same afr at wot. You need to work on idle and transition fueling, and that’s not the jetting.
TT5.9mag
Two atmospheres are better than one
This post by @Rat Bastid is an excellent post and applicable to your situation. Read it and understand it and you’ll be on your way to razor sharp tune up.
@Rat Bastid wrote;
“Hang on before you start changing jets.
You really need to do a few things first. You either need to get a pin set so you can determine the size of the holes in this thing, or at least get some drill bits and use them to figure out the sizes of the holes.
Then you need to get some 6-32, 8-32 and 10-32 brass set screws and the required drill and taps for each size. That way you can make a change to the carb and if you don’t like it, you just screw in a new piece of brass. I get the brass from McMaster-Carr.
The very FIRST thing you need to do is determine the size of the Idle Air Bleed. That’s on top of the carb and it has the bigger of the two holes. The bleed with the smaller hole is the Main Air Bleed. Don’t worry about that one. Yet.
Once you figure out what size the IAB is, you need to find the Idle Feed Restricter in the metering block. It’s a piece of brass and it’s probably up high where it should NOT be.
You need to determine what size it is and then using your drill and 6-32 tap, drill and tap the lower IFR hole and move the IFR jet down there.
As for sizing, that IFR should be .028-.029 and no bigger. Then the ISB should be .068.-.070 to start. Moving the idle feed restricters down and getting the sizing right is critical and must be done before you ever change a jet.
Ive seen the most wacky tune ups come in these carbs. You have to do the work to get the performance and that starts with the idle circuit.
Next up is looking at the emulsion bleeds. On your metering blocks there my be 3, 4 or 5 holes. Doesn’t really matter at this point, what you need to do is deter what size the holes are and how many are open.
As a starting point for a 3 emulsion block, you want to use a .028 hole and use the top and bottom holes. Plug the middle hole.
If you have 4 emulsion holes, use the same sizing and use the top and 3rd hole from the top and block the other two.
If you have a 5 emulsion block, use the same size bleed and use the top and either the 4th or 5th hole. I’d have to see the block to tell you exactly what hole to use.
Usually these carbs have too big emulsion holes and too many. This makes the booster “slug” fuel. What happens is as the signal gets high enough to pull fuel from the booster, you get a big “slug” of fuel. And then you get a big “slug” of air. And it repeats. You can’t fix that with a jet change.
After you get that sorted out and before you change a jet you need to restrict some fuel to the T-slots so you can control how much fuel you get at a cruise.
For the most part, when you are cruising through town or whatever, you are on the T-slots. Most of them today are way too wide and way too long. So to correct that you take your 10-32 tap and correct sized drill and drill into the main body then tap it and use your set screws there.
For your application, I’d say start at .0625 (1/16 inch) and tune from there. You may have to go smaller but its pretty easy to sneak up on it from the rich side rather than the other way.
Once you do all that and you get the thing running well enough to drive it, you want to hook a vacuum gauge to manifold vacuum and see what you have for vacuum at a cruise.
Use that number and take 2-3 off of it and that’s where your power valve should start opening. Do not use 1/2 idle vacuum as that is the wrong way to do it.
If you have 15 inches of vacuum, ideally you’d want a 11.5 or 12.5 power valve, but you can’t get those. 10.5 is the highest you can get so that’s where you start.
If you have 10 inches of vacuum at cruise you’ll want an 8.5 or maybe a 6.5 power valve if you are set up to get on the boosters pretty quickly. That’s controlled a little by emulsion and then by the main air bleed.
When you remove the power valve you will see two small holes. They may be tapped already and have brass in them or not. It’s a crap shoot on that.
The number on the power valve tells you when it opens and those two holes control how much fuel the engine gets when it opens. Changing the number on the power valve will open it sooner or later depending on manifold vacuum. Those two holes control how much fuel the engine gets when the power valve opens.
You need to drill and tap those holes if they aren’t already. Once you understand the power valve circuit and what it really does you can have an incredible tune up that is crisp, clean and it will rival EFI all day long.
Like I said, you still shouldn’t change a main jet. Not just yet. Once you get all the above done as your base line, you can drive the car and see how it responds.
Also, before you drive the car, get the timing curve in shape. I’d start with 18 degrees of initial and 34 total. The curve should start adding timing at slightly over idle speed but no sooner than 1200 RPM. Ideally the curve should continue to add timing until max RPM but that can be time consuming to test. So get it all in by 3200-3400 and start there.
Also, if your distributor has a vacuum advance, use it. It will make the engine run cooler and get far better fuel economy than you will without it.
Now, back to driving the car. At this point you need to understand the relationship between the power valve circuit and the primary main jet circuit. If you don’t understand that, you’ll never get the tune up correct and you’ll suffer from the dreaded “hollyitis” which is solely on the tuner and Holley for decades of bad tuning advice.
The power valve allows the primary main jet to be much smaller than it would need to be at Wide Open Throttle. That’s because at low(er) manifold vacuum that power valve opens, allowing additional fuel to the engine. It really should have been called the “economizer” valve because that’s really what it does.
Once you are at this point, you reduce the primary main jet size 2 numbers at a time until you get a SLIGHT lean surge at a cruise on flat ground. Once you get that, go back up 2 jet sizes and do not change the primary main jet again.
Thats because once you get off the T-slot (I forgot to mention that you need to be at enough throttle opening to be on the main jet and not the T-slots) you are cruising on the primary main jet. You want that jet to be as small as possible for a clean cruise and the best fuel economy.
Once you have the primary main jet dialed in, you can work on WOT tuning.
At this point, with an .0625 restricter in the Power Valve Channel Restricter (the holes you may have had to drill and tap behind the power valve) you need to start 8 jet sizes BIGGER on the secondary main jet. This is because you don’t have a power valve back there.
No matter what, when making tuning changes for WOT you do not change the primary main jet. If you need more fuel for WOT, then add some of that fuel at the secondary main jet and some of it at the power valve channel restriction on the primary side. Make the holes in the brass a few thousandths at a time. You don’t want to add all the fuel at the secondary main jet for WOT. You split it as best you can between the secondary main jet and the power valve channel restricters.
The opposite is true if you need to lean the tuneup out at WOT. Take a couple of jet sizes out of the secondary side and a few thousandths out of the PVCR. Keep making both smaller until your WOT tune is spot on.
As long as you do it this way, your cruise tune up will always be clean and crisp. That’s why once you have the primary main jet sorted out for cruise you don‘t ever change that.
Now you can work on your cruise tune up on the T-slots. When you are hopping around town, screwing the pooch you’ll most likely be on the T-slots unless you run pretty deep gears in the rear axle.
The tune up procedure is the same as tuning the cruise on the primary main jet. You reduce the T-slot restriction until you get a SLIGHT lean surge and then add .003 to the T-slot and send it.
If you bother to do all the work your carb will rival EFI for economy and driveablity AND it will make more power.
Its rather time consuming but well worth the effort in the end.
Just changing main jets to try and unscrew a poorly tuned carb is a fools errand. You’ll never get it right by doing that.”
@Rat Bastid wrote;
“Hang on before you start changing jets.
You really need to do a few things first. You either need to get a pin set so you can determine the size of the holes in this thing, or at least get some drill bits and use them to figure out the sizes of the holes.
Then you need to get some 6-32, 8-32 and 10-32 brass set screws and the required drill and taps for each size. That way you can make a change to the carb and if you don’t like it, you just screw in a new piece of brass. I get the brass from McMaster-Carr.
The very FIRST thing you need to do is determine the size of the Idle Air Bleed. That’s on top of the carb and it has the bigger of the two holes. The bleed with the smaller hole is the Main Air Bleed. Don’t worry about that one. Yet.
Once you figure out what size the IAB is, you need to find the Idle Feed Restricter in the metering block. It’s a piece of brass and it’s probably up high where it should NOT be.
You need to determine what size it is and then using your drill and 6-32 tap, drill and tap the lower IFR hole and move the IFR jet down there.
As for sizing, that IFR should be .028-.029 and no bigger. Then the ISB should be .068.-.070 to start. Moving the idle feed restricters down and getting the sizing right is critical and must be done before you ever change a jet.
Ive seen the most wacky tune ups come in these carbs. You have to do the work to get the performance and that starts with the idle circuit.
Next up is looking at the emulsion bleeds. On your metering blocks there my be 3, 4 or 5 holes. Doesn’t really matter at this point, what you need to do is deter what size the holes are and how many are open.
As a starting point for a 3 emulsion block, you want to use a .028 hole and use the top and bottom holes. Plug the middle hole.
If you have 4 emulsion holes, use the same sizing and use the top and 3rd hole from the top and block the other two.
If you have a 5 emulsion block, use the same size bleed and use the top and either the 4th or 5th hole. I’d have to see the block to tell you exactly what hole to use.
Usually these carbs have too big emulsion holes and too many. This makes the booster “slug” fuel. What happens is as the signal gets high enough to pull fuel from the booster, you get a big “slug” of fuel. And then you get a big “slug” of air. And it repeats. You can’t fix that with a jet change.
After you get that sorted out and before you change a jet you need to restrict some fuel to the T-slots so you can control how much fuel you get at a cruise.
For the most part, when you are cruising through town or whatever, you are on the T-slots. Most of them today are way too wide and way too long. So to correct that you take your 10-32 tap and correct sized drill and drill into the main body then tap it and use your set screws there.
For your application, I’d say start at .0625 (1/16 inch) and tune from there. You may have to go smaller but its pretty easy to sneak up on it from the rich side rather than the other way.
Once you do all that and you get the thing running well enough to drive it, you want to hook a vacuum gauge to manifold vacuum and see what you have for vacuum at a cruise.
Use that number and take 2-3 off of it and that’s where your power valve should start opening. Do not use 1/2 idle vacuum as that is the wrong way to do it.
If you have 15 inches of vacuum, ideally you’d want a 11.5 or 12.5 power valve, but you can’t get those. 10.5 is the highest you can get so that’s where you start.
If you have 10 inches of vacuum at cruise you’ll want an 8.5 or maybe a 6.5 power valve if you are set up to get on the boosters pretty quickly. That’s controlled a little by emulsion and then by the main air bleed.
When you remove the power valve you will see two small holes. They may be tapped already and have brass in them or not. It’s a crap shoot on that.
The number on the power valve tells you when it opens and those two holes control how much fuel the engine gets when it opens. Changing the number on the power valve will open it sooner or later depending on manifold vacuum. Those two holes control how much fuel the engine gets when the power valve opens.
You need to drill and tap those holes if they aren’t already. Once you understand the power valve circuit and what it really does you can have an incredible tune up that is crisp, clean and it will rival EFI all day long.
Like I said, you still shouldn’t change a main jet. Not just yet. Once you get all the above done as your base line, you can drive the car and see how it responds.
Also, before you drive the car, get the timing curve in shape. I’d start with 18 degrees of initial and 34 total. The curve should start adding timing at slightly over idle speed but no sooner than 1200 RPM. Ideally the curve should continue to add timing until max RPM but that can be time consuming to test. So get it all in by 3200-3400 and start there.
Also, if your distributor has a vacuum advance, use it. It will make the engine run cooler and get far better fuel economy than you will without it.
Now, back to driving the car. At this point you need to understand the relationship between the power valve circuit and the primary main jet circuit. If you don’t understand that, you’ll never get the tune up correct and you’ll suffer from the dreaded “hollyitis” which is solely on the tuner and Holley for decades of bad tuning advice.
The power valve allows the primary main jet to be much smaller than it would need to be at Wide Open Throttle. That’s because at low(er) manifold vacuum that power valve opens, allowing additional fuel to the engine. It really should have been called the “economizer” valve because that’s really what it does.
Once you are at this point, you reduce the primary main jet size 2 numbers at a time until you get a SLIGHT lean surge at a cruise on flat ground. Once you get that, go back up 2 jet sizes and do not change the primary main jet again.
Thats because once you get off the T-slot (I forgot to mention that you need to be at enough throttle opening to be on the main jet and not the T-slots) you are cruising on the primary main jet. You want that jet to be as small as possible for a clean cruise and the best fuel economy.
Once you have the primary main jet dialed in, you can work on WOT tuning.
At this point, with an .0625 restricter in the Power Valve Channel Restricter (the holes you may have had to drill and tap behind the power valve) you need to start 8 jet sizes BIGGER on the secondary main jet. This is because you don’t have a power valve back there.
No matter what, when making tuning changes for WOT you do not change the primary main jet. If you need more fuel for WOT, then add some of that fuel at the secondary main jet and some of it at the power valve channel restriction on the primary side. Make the holes in the brass a few thousandths at a time. You don’t want to add all the fuel at the secondary main jet for WOT. You split it as best you can between the secondary main jet and the power valve channel restricters.
The opposite is true if you need to lean the tuneup out at WOT. Take a couple of jet sizes out of the secondary side and a few thousandths out of the PVCR. Keep making both smaller until your WOT tune is spot on.
As long as you do it this way, your cruise tune up will always be clean and crisp. That’s why once you have the primary main jet sorted out for cruise you don‘t ever change that.
Now you can work on your cruise tune up on the T-slots. When you are hopping around town, screwing the pooch you’ll most likely be on the T-slots unless you run pretty deep gears in the rear axle.
The tune up procedure is the same as tuning the cruise on the primary main jet. You reduce the T-slot restriction until you get a SLIGHT lean surge and then add .003 to the T-slot and send it.
If you bother to do all the work your carb will rival EFI for economy and driveablity AND it will make more power.
Its rather time consuming but well worth the effort in the end.
Just changing main jets to try and unscrew a poorly tuned carb is a fools errand. You’ll never get it right by doing that.”
If you are going to do that tuning stuff, get a pin gauge set to measure what is in the carb now, so adjustments can be made based on what you see now.
It is an exercise, but, it makes a huge difference when you get it sorted out and right.
Pin Gauge set, 61-80 drill set, 1-60 drill set, brass/taps and you are off and running.
One of the best emulsions in a carb was the original 3310 style vacuum carbs. Someone started making metering blocks with 4 and 5 emulsions and industry "Monkey see/monkey do" nonsense started and the pooch began to get screwed.
It is an exercise, but, it makes a huge difference when you get it sorted out and right.
Pin Gauge set, 61-80 drill set, 1-60 drill set, brass/taps and you are off and running.
One of the best emulsions in a carb was the original 3310 style vacuum carbs. Someone started making metering blocks with 4 and 5 emulsions and industry "Monkey see/monkey do" nonsense started and the pooch began to get screwed.
Inertia
Well-Known Member
I've got an ancient kit for old bleeds .
Love passing this stuff/knowledge on .
Love passing this stuff/knowledge on .
TT5.9mag
Two atmospheres are better than one
Interesting. I have a few of those carbs. I’ll have to pull the blocks off and have a look.
nfhDODGEnfh
Well-Known Member
That's great info, thanks. Hopefully on Wednesday me and Inertia can get it dialed in better. Also I can't wait to get the new street slicks on and see how that feels on the launch!
nfhDODGEnfh
Well-Known Member
Got some help from Inertia today at his shop, we messed with carb a bit and figured out it was a bad pcv valve that was causing some of the rich condition at idle. Changed it to a different pcv he had laying around and messed with the mixture screws, that brought the idle up to 13.0. So that was a positive step without drilling air bleeds yet. Still needs a bit of work as it's rich on light acceleration, in the low 11s. Wide Open Throttle was high 11s low 12s so maybe a jet change down would be a worth while try aswell? but I can cruise in 3rd or 4th at low rpm now and it's about 13.4 so that's much better than before.
I never thought it could have been the pcv causing the idle curcuit to be so rich. We will continue to chip away at it over the coming Weeks and see how much more dialed in we can get the carb. But today was definitely a step in the right direction.
Also got the new street slicks on and they are waaaay better than the bfg radials I had on. Slamming secound gear shakes my dash instead of spinning tires.
TT5.9mag
Two atmospheres are better than one
The pcv valve is basically a large controlled vacuum leak. If the carb was tuned originally with the pcv and it is removed the tune up should also be changed. They can and will make a difference in the idle tune up. Your next step should be pinning every single hole in the carb. Do not make any changes until you know what size every orifice is and have them written down. That’s step 1
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