Carburetor wizard part 2

[Cheapsunglasses]

So I understand the function of the metering rods, vacuum controls them, I was thinking if you wanted to delay, you go stiffer, not weaker. But it makes sense that’s not the case. When you put the stronger spring in it, makes it open quicker, because the strong spring doesn’t require as much vacuum. When you put a lighter spring in, it has to fight the vacuum more.


(I understand the concept, but I may not be explaining it correctly )

 

[Geoff 2]

Cheap.
Carb is not to big. Big carbs do not cause idle problems [ varying AFRs ] ifffff they are adjusted properly. Adjusted properly means three things:
- at idle, in gear if auto, there is 0.060" [ or less ] of transfer slot showing below the pri blades. 0.020" to 0.040" is ideal & leaves more of the t/slot for transition to the main cct.
- t/blades [ all 4 of them ] return to the same position every time. There is air going past the blades at idle. Obviously if one is binding on the gasket, say, & not fully closing, more air gets past & idle rpm increases. Occasionally, when the carbs are assembled, the blades might not have been centered properly & binding occurs in the bore.
- no vac leaks.

To select the correct piston springs: loosen piston covers, swivel slightly so that piston is in view but captured. Tighten cover screw. With engine warmed up, idling, in gear if auto, pistons should be down, not moving. Install stiffer springs & repeat test until piston starts to move. Bottom line: you want the stiffest spring that stops piston movement. This ensures instant throttle response.

 

[Cheapsunglasses]

Thanks Geoff, I’ve used the factory orange spring, pink, and silver spring, and back to pink. Every spring change, I’ve always had great throttle response, probably why I’m looking past the springs.

Even though it’s a little rich, that’s better than too lean. A guy I work with is having a retirement party today, he’s a mopar guy so I figured taking the car to work would be cool. I can adjust the carb in the parking lot if I need to.

 

[Some Car Guy]

Springs are a fine tuning adjustment. just can’t be moving at idle. Tune you rods and/or jets and then change the springs if needed.

 

[1967coronet]

AF readings are good to have and seem to be a very good tuning tool.
But.... have you pulled the plugs and checked them ?

 

[Cheapsunglasses]

I wanted to get some actual driving done for an accurate reading, instead of some short around the block trips.

I drove it 30 miles to work, 70mph, and then a little town driving. It was pretty consistent in the 12 range, a little into the 11s. I love this carb, 66 degrees this morning didn’t need any warmup, it was ready to go. It pulls nicely, cruises great.

 

[Cheapsunglasses]

Life’s been a little busy I haven’t been able to play with it until today. I watched an Uncle Tony video talking about tuning these carbs, and realized my carb had the accelerator rod in the hole closest to the carb, which is the most, so I moved it to the middle, in his words “closest to the carb is for race car guys, furthest is for street guys, middle is for the people that don’t know what they are.” I put the pink spring back in the metering rod, and I thought 5.5psi on my fuel was ok, but I got to reading and people say 4-6, I decided to drop 1/2 a pound, and try messing with the idle air screws. It doesn’t idle as smooth as before, but it’s idling at 13:1, it cruises at the 12s, and heavy throttle is in the 10s. If I a 68/57 rod in instead of a 65/52 with the .101 jet, it leans it out too much for a few seconds. It seems happiest with the 101 jet and the 65/52, which is tune 4.

I’m a little curious on the idle being a little more ruff, but the afr is good, so I guess it’s fine.

 

[furious70]

Is the idle afr consistent now once warmed up?

If so, go back around to timing and adjust for best vacuum. That OEM cam shouldn't need to be too rich at idle.

10's at wot is way richer than you want to be. Even if it feels good it's laying over pig rich, will soot your valence and foul your plugs.

If a correct wot afr causes a bog or surge it's not the main jets' fault, it's the transition circuits (accel pump, springs on the rods). Don't crutch those with too large of a main jet

 

[Cheapsunglasses]

Afr is pretty consistent. I know 10 is rich, I guess I can adjust the secondary air door, make it open sooner. Or would softer metering rod springs be a better idea?

My main and secondary jets are the leanest ones in the kit, I’m guessing I’m not over jetting it. And my idle screws are just shy of a full turn out, so I think I’m not over correcting there either. My idle is at 750rpm, which might be a little low.

 

[furious70]

I know the calculations for jet orifice surface area get tedious on a carterbrock, but you may need bigger jets and bigger rods to end up with less exposed surface area. It's more complicated than jetting a Holley. You have to do that sometimes because of the limited choices of steps in the rods.
You're richer then you need to be at cruise and wot so you need less surface area in both places. Get all the afr's where you're happy steady state and then tune the transitions.

 

[furious70]

With that mild cam a cruise of 13.5:1 and wot of 12:1 should be fine

 

[Cheapsunglasses]

I’m having a bit of trouble understanding, probably because I don’t fully understand what I’m doing

Going by the chart, I’m on tune 4, which is the leanest, but you’re suggesting going up a jet size?

 

[furious70]

I missed that before, you're at 4 and still that rich? My experience has been the opposite of some others, these carbs normally are lean out of the box for me.
Do you have another carb to compare?

 

[Cheapsunglasses]

I’ve had a factory 71 440 avs that was too lean, and a 67 440 afb that was too rich. I bought the Edelbrock so I’d have a tuning kit and a chart. It’s a 69 Chrysler Newport 350hp 440, with 440 source heads, and the regular 440 performer intake. I do have a small 4 hole spacer, mostly for keeping the carb off the intake, but could that be causing the issue?

 

[furious70]

No.
Tell us more about how the O2 sensor is installed

 

[Cheapsunglasses]

It’s an AEM, and I have it as close to 18” away from the manifold collector as I can get it, and it’s at a 90 degree angle, best I could do

 

[Some Car Guy]

Spacer is fine. You need to lean this deal out. I wouldn’t worry about going away from some set tune scheme they list. Just get a leaner rod in there. Easy enough to go out with a screwdriver and do some driving. Just swap it around a few times in a parking lot and you’ll have this. I dial stuff in that way. You have an o2 sensor so this should be cake with a carterbrock.

 

[Geoff 2]

Four hole spacer is ok, will not cause tuning problems.

Less than one turn on the mixture screws tells me that you have too much transfer slot exposed, best is 0.040" or less at idle. Remove carb & check. If more than 0.060", drill a 3/32" hole in the forward section of each primary t/blade. This is part of the tuning process & until you get this relationship CORRECT, the engine is never going to run well. Keep enlarging the holes in 1/64" increments, re-adjusting the mixture screws each time [ they will need to be to be backed out ] until you have 0.040" or less of T slot below the blades at idle. Yes, I know it is a pain removing/installing the carb....Report back.

Forget about AFR readings at this stage & go by 'feel'. I have been tuning carbs for 50+ yrs without EVER using an AFR meter, & keep getting new jobs/engine builds by referral. So I think I must be doing something right....

 

[Cheapsunglasses]

Spacer is fine. You need to lean this deal out. I wouldn’t worry about going away from some set tune scheme they list. Just get a leaner rod in there. Easy enough to go out with a screwdriver and do some driving. Just swap it around a few times in a parking lot and you’ll have this. I dial stuff in that way. You have an o2 sensor so this should be cake with a carterbrock.

That’s the biggest reason I like the Carter/Edelbrock. I was making some of these changes with the engine running on the side of the road!

 

[furious70]

I would suggest that a 440 with the 350hp cam should never need holes drilled in the butterflies in order to idle on the idle circuit. There's something else wrong.