Secondary metering rod size?

[RustyPile]

Back in the first few years of my racing, I ran "stock" then highly modified Q-jets --- the rules dictated carburetor requirements.. By design, the Q-jet is pretty forgiving on the tune, especially on a stock or near stock engine.. There are so many variations in it's "geography" and parts being specific to a particular series, it's easy to get way off track with the tuning. I see this a lot with the over-the-counter rebuilt units being sold today. Add this to the fact that most "back yard builders" just don't have a thorough understanding of carburetors in general...

@3504boltmain, before you get too deep in swapping out those secondary rods and jets, take a look at the opening "time" and duration of the secondary air metering valve.. That's the big choke looking flap at the top of the secondary bores.. Linkage to the choke pull modulates it somewhat, and some models had a separate vacuum control for the secondary air valve. Also, there's a coil spring at the end of the shaft that controls the rate of opening.. If the air valve opens too soon or too quickly, it can cause the high speed stumble you describe..

I tend to agree with Donkey **** about the Factory TBI vomit system.. and also Holley as being a better choice today between it and a Q-jet..

 

[RustyPile]

You must be registered for see images attach

No way, slobberjet

Have you had a chance to put it through the paces since you built it??

 

[Honky Kong jr]

Have you had a chance to put it through the paces since you built it??

Hell no to cold I only did it 1/1/18 lol

 

[RustyPile]

Hell no to cold I only did it 1/1/18 lol

Oh.... I guess I misunderstood the post in your other thread.. When you were describing building it I thought it was something you did a while back..

 

[Honky Kong jr]

Oh.... I guess I misunderstood the post in your other thread.. When you were describing building it I thought it was something you did a while back..

Nope I got the main body for myself as a Jesus birthday gift.

 

[3504boltmain]

Back in the first few years of my racing, I ran "stock" then highly modified Q-jets --- the rules dictated carburetor requirements.. By design, the Q-jet is pretty forgiving on the tune, especially on a stock or near stock engine.. There are so many variations in it's "geography" and parts being specific to a particular series, it's easy to get way off track with the tuning. I see this a lot with the over-the-counter rebuilt units being sold today. Add this to the fact that most "back yard builders" just don't have a thorough understanding of carburetors in general...

@3504boltmain, before you get too deep in swapping out those secondary rods and jets, take a look at the opening "time" and duration of the secondary air metering valve.. That's the big choke looking flap at the top of the secondary bores.. Linkage to the choke pull modulates it somewhat, and some models had a separate vacuum control for the secondary air valve. Also, there's a coil spring at the end of the shaft that controls the rate of opening.. If the air valve opens too soon or too quickly, it can cause the high speed stumble you describe..

I tend to agree with Donkey **** about the Factory TBI vomit system.. and also Holley as being a better choice today between it and a Q-jet..

Yeah, I adjusted the air metering valve several times. loose moderate and tight.. no change. I also adjusted the choke, mixture screws, fast idle, timing, ran the truck without vacuum to the vacuum advance and egr. Still no change. I put the hand made secondary rods in and revved it in the driveway but it sounds like crap. And like Honky Kong jr, It's been cold and snowy... And my tires are cooked. . Other stuff I've done:

Checked Compression: 90 psi-ish across the board
Checked vacuum pressure: steady and in the green
New fuel pump and filter
New plugs, wires distributor cap, rotor, coil and ignition module.
Cleaned out the gas tank (The inside liner came apart... I was pulling sheets of the stuff out of there.)
Disconnected the auxiliary tank switching solenoid.
Cleaned up the springs and weights and tested the pick up coil electrically.

I will plan to get a new distributor, but I don't want one of those flashy Holley's sitting on my engine. Yuk, It reeks of "Tuner" Might as well get a sticker that says "This Sticker Adds Five Horse Power"!

 

[RustyPile]

Get rid of the EGR. Don't just disconnect it, toss the sumbitch in the trash and block off the ports in the manifold!!!!. Those things are nothing but a pain in the ass.. Their operation effects everything about an engine.. When faulty, they cause hesitation, poor performance, poor gas mileage, rough idle, stalling, pinging,-- just about everything..

I have always adjusted the air valve simply by "feel".. There's no way I could put in writing and explain the technique to someone with not a lot of "seat time" on Q-jets.. Air that's sucked in by the engine is what opens the valve.. That plunger/piston connected to the metering rod hanger is a power valve.. It needs the correct spring under it for proper operation..

90# of compression tells me either you have mighty big combustion chambers or the rings are quite leaky.. Either way, the volumetric efficiency of the engine is way down.. You need some resistance in the "delay" spring, don't want the valve just flopping open.. "In the green" manifold vacuum doesn't tell me much, give me a number.. With the vacuum advance disconnected the average SBC likes about 32 - 34 degrees total advance, Depending on the engine something between 4 -- 10 initial, with all of it in around 2,000 -- 2500 RPM.. With the vacuum advance connected, you should see around 46 - 50 degrees at light load cruise speeds.. With a healthy engine, you can push these numbers somewhat...

 

[74 Shortbed]

I don't want one of those flashy Holley's sitting on my engine. Yuk, It reeks of "Tuner" Might as well get a sticker that says "This Sticker Adds Five Horse Power"!

Not a flashy one just a stock one, but it's just like any other carb or anything for that matter, if you don't understand what the parts do and how they function and their purpose, you'll never get it to work, Holley is about the easiest and simplest to tune, only one other that I can think of that's simpler is the Autolite 4100, but then again if you don't know how it works you'll never get it to work, just sayin..

 

[Honky Kong jr]

The shiny ( flashy) part has a purpose.

 

[74 Shortbed]

What, to look purdy..

 

[Honky Kong jr]

What, to look purdy..

Yeah cuz bitches like shiny ****....... lol

 

[74 Shortbed]

Yeah cuz bitches like shiny ****....... lol

LMAO..... Have you messed with it yet???.

 

[Honky Kong jr]

LMAO..... Have you messed with it yet???.

To cold. Supposed to get up in the 50s this week but rain, so it might be a while.

 

[74 Shortbed]

To cold. Supposed to get up in the 50s this week but rain, so it might be a while.

Thought you liked that cold ****, lol, rain sucks too though when you want to do stuff.. lol.

 

[Honky Kong jr]

Thought you liked that cold ****, lol, rain sucks too though when you want to do stuff.. lol.

No I hate the cold and rain does suck