Runs better with vac advance unhooked (Help)

[350runner]

Have you tried changing anything?

Sent from the dust in front of you!

 

[73 C10]

In post #4 i described the last changes. They made the difference.

I've been keeping my signature up to date as I find out more.

I'm wondering if this might be a needle or needle spring thing.

I thought the weights spring and va were performance/economy improvements. I will still be looking into those sujestions but I didn't think you guys were suggesting it necessary to solve the sputter. If i'm wrong I'll buy the parts.

What did I miss. Should I change the base timing from 12 to 14 or 16?

 

[rich weyand]

I think you are down to mixture. Sounds a bit like lean sag on the cruise circuit.

 

[73 C10]

Hi Rich,

Is the 30 mph sputter a clue? That's why I ask about the needle springs (step up springs ?) or needle size.

I plan to get the gasket and crack it open to find the jet sizes. I think I remember seeing 395 or 398 on them. Now that I know how Edlebrock labels there jets I know that they all say 120-3or4xx. I guess 120 would be OD size or shape identifier.

 

[rich weyand]

Yeah, I think 120 is the product series number.

8" step-up springs with your engine. It pulls so much vacuum otherwise you won't get into the power position unless you are full on it. I actually stretched the 8" springs 1/4" to get them closer to 9" of vacuum.

Crack the carb and report back on jets and needles. The needles will have the diameters stamped on them, like "6252" for .062 + .052.

I had this same issue and tuned it away. No issues now.

 

[73 C10]

I noticed I did something stupid. When I made the changes in post #4. I had tried va on the timed port (sputtering leaving idle to slow cruze and cruzing 30-40 mph), then I thought I switched to the right port. What I really did was loose track of the hose in the dark, grabbed the old leaky hose that I left sitting close by. I didn't pull it out yet because it was zip tied to the wiring loom. So I guess I grabbed it accidentally and plugged it into the right port and capped off the left.

So I was running with no va and a leaking manifold port on the carb because the other end off the hose was wide open, just sitting there. Like usual, it runs better without the vac advance, but I think it is making it hard to start (wet fouled?). When I went to get the kit I had it like this and it didn't want to start when I left the store. It usually fires right up.

So now that I admitted my rookie mistake, I have the va on the right port, left capped off.

I also bought the kit for the carb. I popped in the 8" springs and drove into work this morning. I had a bog coming off idle once and the same sputtering in the low cruise off idle speeds.

I see the needles are 7547 (stock spec). I put in the yellow 4" springs (stock spec).

 

[73 C10]

Without measuring, the old springs I pulled out look like the new 4" springs I just put in. Just dirtier. The spring in the picture is the 8" I drove in with this morning next to the old dirtys.

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[rich weyand]

.... So now that I admitted my rookie mistake, I have the va on the right port, left capped off.

I also bought the kit for the carb. I popped in the 8" springs and drove into work this morning. I had a bog coming off idle once and the same sputtering in the low cruise off idle speeds.

I see the needles are 7547 (stock spec). I put in the yellow 4" springs (stock spec).

Left port/right port from the front, or from the driver's perspective? You should use driver's perspective, so "left" is always driver's side, and "right" is passenger side. In which case, you have it hooked to ported vacuum.

7547 is way lean in cruise. That's the problem. You have lean sag on the cruise circuit.

And you really need those 8" springs in there.

Did you crack the carb and figure out what jets are in it?

Assuming stock .098 primary jets, you should be running something like Edelbrock 1461, .065 and .057.

 

[73 C10]

Sorry. Va is on the left (always on) port, right capped. Hooked up the other way ran like crap.

I bought the:
Calibration Kit #1487 for
#1406 includes:
-Metering Rods (Pair)
.070 x .037
.073 x .042
.073 x .047
-Metering Jets (Pair)
.095
.098
.101
-Complete set of step-up springs

So I don't see that rod in the kit. I know where I can maybe get the pair by them selves. I haven't had to open the kit yet and I have a pack of springs already. Should I return it? Or should I try any of the configurations in the kit? The one you suggest is not even on the chart I'm looking at. Here it is:

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I do see it in this chart for another model and it goes with a huge .113 main. Here:

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I'll try it if you say so.

I didn't find a gasket, so I haven't opened it yet. But I will open it when I get home from work and try to reuse the one I put in a few days ago.

 

[73 C10]

Ok. It's all stock. 98 primary, 95 secondary, 7547 needle, yellow 4" springs. I hear you on the 8" springs. So should I grab the 6557?

I tried a 98 in secondary (richer), .073 (richer) .037 (richer), 8". It's still missing from idle to 30ish with a light foot.

 

[rich weyand]

Yeah, you're still way lean on the cruise circuit. (.098 with .073 rod is .025 difference)

You have almost the same engine setup as me, so I would either go to a .095 primary and a .062/.052 rod, or stick with the .098 primary with a .065/.057 rod. You can buy this part at JEGS or Summit. Summit is closer to you.
http://www.summitracing.com/parts/edl-1461

Gasket (5 per pkg) is Edelbrock 1499.
http://www.summitracing.com/parts/edl-1499

The 1406 is optimized for mileage, which means the cruise circuit is way lean. The 1405 is optimized for performance. Note the stock setup there: .100 jet with a .070 rod at cruise, which is .030 difference. That's why I say a .065 with the .098 jet. I'm running a .062 rod with the .095 jet. About .033 difference.

 

[73 C10]

Ok. Stuffs ordered. I'll report back in a couple days.

 

[rich weyand]

BTW, to compare tunes, since jets and rods act on cross-sectional area, you need to compare the difference of the squares. Take the square of the jet diameter minus the square of the rod diameter:

0.1 0.07 0.0051
0.098 0.065 0.005379
0.095 0.062 0.005181

These three tunes are about the same. Compare that to what you have now:

0.098 0.075 0.003979

You are getting less than 80% of the gasoline than the stock tune in the 1405, or that I get in a similar setup with my tune set with an AF/R meter. If the 1405 tune is between 14.25:1 and 14.5:1 (as is mine), 20% less gas is between 14.25:.8 and 14.5:8, which is same as between 17.8:1 and 18.1:1. That's so lean, it's on the edge of not firing that mixture at all.

I'll be very interested to hear your news once you get the new rods installed.

 

[73 C10]

Well, bummer. I decided on the "stick with the .098 primary with a .065/.057 rod." option. It still misses. No change.

I did buy the other rods so I could do the "go to a .095 primary and a .062/.052 rod" option.

I also set the valves while checking for bent rods.

The timing stuff I ordered is still on the way, and it's in Hodgkins, IL, on the way to California, so a couple more days until I can mess with the timing.

I should have new plug wires tomorrow.

If I got an A/F tester, would I just screw it into the #8 runner? How does that work? Oh, O2 sensor in the exhaust?

 

[rich weyand]

O2 sensor in the exhaust pipe right behind the header flange.

You should be a lot closer to correct mixture now, so I don't know that the A/FR meter is a requirement -- yet. No change when making that big of a mixture change means there is something else wrong you need to fix first.

Can you tell if it is always missing on the same cylinder? One way to tell is to pull off one plug wire, and see if there is just one solid miss, and no other misses. If you still have another intermittent miss in addition to the solid miss, then you replace the plug wire and move on to the next one. That could narrow your focus to a single cylinder.