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1974 K10 Dirty Sancho

Saved from cruel and unusual punishment
Overview Gallery Discussion
I remember my 64 C10 we put a 350 in it and about a year and half later it was running like crap. Replaced the spark plugs and it was running like a top again. Granted this was 25 years ago so I don't remember details, just that new spark plugs fixed the crapping running even tho I was sure it was going to be more difficult.
 
If that's one of the spark plugs as they are now, that thing is definitely way rich. Did you go into the 1406? Out of the box, they are too rich on the primaries, and too lean in the secondaries. It could be possible that the guy you got it from didn't open it up either.
I would start by taking the top off and see what jets are in it. (It's a pain to read the numbers!) And also find out what springs are under the power piston that holds the rods. It could have too big of jets, and too stiff of springs that are not getting pulled all of the way down at idle, because of the vacuum that the engine is pulling. Around here, I start with the blue ones, which are the lightest, and then move up one step if needed.
 
6872xtc said:
If that's one of the spark plugs as they are now, that thing is definitely way rich. Did you go into the 1406? Out of the box, they are too rich on the primaries, and too lean in the secondaries. It could be possible that the guy you got it from didn't open it up either.
I would start by taking the top off and see what jets are in it. (It's a pain to read the numbers!) And also find out what springs are under the power piston that holds the rods. It could have too big of jets, and too stiff of springs that are not getting pulled all of the way down at idle, because of the vacuum that the engine is pulling. Around here, I start with the blue ones, which are the lightest, and then move up one step if needed.
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I have no idea what was done to the carb but the guy I bought it from said his uncle hopped it up for a built SBC. My carb knowledge is limited however I did pop the top off the carb and I replaced the accelerator pump while I had it apart. IIRC I bought a rebuild kit for it but I can't remember all that was included with it. Here are a few pics I took when I popped the top off the carb.

IMG_5861.JPG

IMG_5862.JPG

IMG_5864.JPG

IMG_5865.JPG
 
Well then I would just assume that the guy didn't get things right, or it's just that wrong for your engine.
I would start with 95 jets in the primaries with 7047 or 7147, or even 7347 rods. The first 2 digits of the number is the size in the cruise mode, when the rods are pulled down. During low vacuum, the rods are pushed up by the springs and it runs in the smaller diameter. That's the 47, or whatever you pick out. I have just always had good luck finding the "47" sizes. And I then just change the secondary jets to get more when I mash on it.
The smaller the rod size, (lower number) the richer it will run.

The stiffer the step-up springs are, the faster it will richen up when the vacuum drops. So if it has the stiffest springs, and you don't have enough vacuum to hold them down, it will be enriched by that at idle, or just off idle.

I would get at least 104 or possibly larger jets for the secondaries. It depends on what size the rods have in the power section. (The 2nd half of the number)

And most of my knowledge on these carbs was passed on to me from @500$k5 .
:saweet:

I can tell you more if you want, let me know what you find.
 
6872xtc said:
Well then I would just assume that the guy didn't get things right, or it's just that wrong for your engine.
I would start with 95 jets in the primaries with 7047 or 7147, or even 7347 rods. The first 2 digits of the number is the size in the cruise mode, when the rods are pulled down. During low vacuum, the rods are pushed up by the springs and it runs in the smaller diameter. That's the 47, or whatever you pick out. I have just always had good luck finding the "47" sizes. And I then just change the secondary jets to get more when I mash on it.
The smaller the rod size, (lower number) the richer it will run.

The stiffer the step-up springs are, the faster it will richen up when the vacuum drops. So if it has the stiffest springs, and you don't have enough vacuum to hold them down, it will be enriched by that at idle, or just off idle.

I would get at least 104 or possibly larger jets for the secondaries. It depends on what size the rods have in the power section. (The 2nd half of the number)

And most of my knowledge on these carbs was passed on to me from @500$k5 .
:saweet:

I can tell you more if you want, let me know what you find.
Click to expand...

Good info, thank you. Here’s what I found....

7547 metering rods

B90FA3BE-CA76-4740-89C6-38921A9362D5.jpeg

F677BD98-9B9D-4A7E-A8FC-E678B6C9D14C.jpeg
 
Correct me if I'm wrong it's been awhile but you can get a idea if you measure the opening with a drill bit or even better small calipers.
 
Babaganoosh said:
Correct me if I'm wrong it's been awhile but you can get a idea if you measure the opening with a drill bit or even better small calipers.
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I’m leaning toward picking up a kit so I can take the guess work out of it.

BD54314B-E95D-4FAC-BE1C-DF03AD0F0884.jpeg
 
There are still some remnants of the numbers on the jets, but those have been beat up some. I have found the numbers difficult to read often because of poor stamping without damage, so those are in sad shape. Functionally, they are probably fine, but knowing what you have is the problem. So with those rods, you would could have a 98 and be somewhere in the ballpark, I believe, but the power mode would be rich from what I remember seeing here. This of course is subject to change due to your elevation. I am at 4700' but we can see the relative altitude up around 7000' or higher at times.
This picture shows a "factory "98" out of a carburetor on the left and a 100 that I purchased as a pair in a package. The markings are a little different.
The springs are, from left to right, blue, orange and pink. (Blue are used)

A kit doesn't take the "guess work" out of it, and if it doesn't have the correct parts in the long run, you only use about half of it. The kit may get you some parts for a decent price that gets some of the problem though. So it's your call. But I would bet that you won't have enough jet in that kit for the secondaries to pull as hard as they could.

15711071390607906764069199992542.jpg
 
I am wondering if you have the plain springs which would make the piston step up too fast, too often, maybe not pull down at idle.

Do you know how much vacuum it pulls at idle?
 
6872xtc said:
I am wondering if you have the plain springs which would make the piston step up too fast, too often, maybe not pull down at idle.

Do you know how much vacuum it pulls at idle?
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Nope, haven’t checked the vacuum yet but I remember Mark telling me to do that. I’m about 10 stories over sea level btw.
 
Ya know, if you put a Q-jet on it, @Bent77 could probably dial it in really well, especially if you let him run it on the dirt circle track!!
:D :waytogo:
 
skunked said:
I’m leaning toward picking up a kit so I can take the guess work out of it.

View attachment 317583
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Completely agree, think what I was going after was a idea where to start so you could either go down or up.

When I rejetted my quadrajet I was able to find old GM parts manuals and I picked close to my elevation and left it.
 
I went deep into my archives last night and found some old dusty history books pertaining to carb tuning in effort to figure out which meter setup I should run for my application. Through my research I found a reference to manifold design, specifically square bore VS spread bore and the symptoms one would have if they ran a 1406 style carb (square bore) on a spread-bore manifold. Apparently there are some ports that would be open therefore causing a vacuum leak which would then cause a rich condition at idle :thinking: I didn't have time to pull the numbers off my manifold however I was able to locate some old photos on my PC from the manifold swap right before I installed the Q-Jet. Looky there.....:doah:
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I need to go dig around the shop to see if I have one of these, otherwise I'll order one....

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