Secondary metering rod size?

[3504boltmain]

I lot of people hate the QJ. I like it.

First off, there are many, many adjustments which can be made/messed up.

Hesitation means a couple of things.

First the accelerator pump may not be acting or acting too slowly. There should be two holes to put the linkage in on the accelerator pump. The one closest to the fulcrum will make it act more quickly. I have found the newer kits have pumps which tend to come apart in that the cup comes off of the holder and the pump no longer works. Find one that it not thin blue silicone cup.

Primary metering rods are all the same diameter on the thin end. Jet size determines low vacuum mixture. Different rods have different diameters on the thicker part, and the combination of three factors determines cruise mixture...jet size, rod size and rod depth. Depending on the year, there are two ways to control rod depth. The earlier ones had a soft plug below the fuel filter which had to be drilled out to expose a screw. Later ones have an adjustment which can turned from the top of the carb. The deeper the rods go with vacuum, the leaner the cruise mixture.

Secondary control flap is actually the venturi of the secondaries, and has a few adjustments. The flaps are off center and demanded air flow will pull them open. Their bend is the actual venturi of the secondaries. There is a spring which closes it against air flow which if broken or too loose will cause bogging at WOT by allowing the secondary control flap to be open wider then the air flow requires. There is a flat blade screw on the side near the fulcrum for the control flaps and an allen set screw underneath for this spring, which near the fulcrum/shaft of the secondary control flaps. Secondary metering rods are simple and strictly mechanical based on how far open the control flaps are.

There is a vacuum diaphram which normally is the choke pulloff AND secondary shut down. This will cause the secondaries to taper off as you build manifold vacuum...reach speed. There is also a mechanism to disallow the secondary throttle plates from opening if the choke is not fully open...as in "engine too cold for WOT".

All of these things need to be operational for a QJ to work right, but when they are you have good economy with your foot out of it and ample power when needed.

You are very correct here. I did have this bogging issue since before the rebuild.. The problem I have is that I can't get it to bog in the driveway(in Park). It only does it when in gear. So it's been very hard diagnosing the issue. I will look at where the accelerator pump is hooked to on the linkage.. Thanks for that tip. I have CN stamped secondary rods and I can't find information that tells me exactly which rods I should have. I have adjusted and readjusted my fuel mixture screws quite a bit too. I have also adjusted and readjusted the secondary control flaps too. I have also checked the choke lockout... It clears way for the secondary's to open up when warmed up. I should go get a more legit stock C10 and swap parts with this truck to quickly find the issue.
I do agree with RustyPile that the carb could have been hacked and it is junked out... Maybe a quick swap with a known good one will answer that question... But maybe its just the low compression as mentioned earlier.

DoubleDingo, I hope this answers your questions. Thanks to all for the input.

 

[DoubleDingo]

Yes, a good carb that hasn't been hacked will be a good place to start. Keep us posted on the results of your hard work.

 

[3504boltmain]

RustyPile , As per Lars Grimsrud's Testing method, It appears my power piston is jammed.

 

[RustyPile]

RustyPile , As per Lars Grimsrud's Testing method, It appears my power piston is jammed.

Soooo.... You didn't read post 103.. Instead you engaged the help of an aero space engineer???? lol...... Works for me...

 

[3504boltmain]

In all your explanations, you've not mentioned the accelerator pump operation.. When addressing a hesitation, it's the quickest and easiest to check.. Doesn't even require the first tool -- eyes and hands only..

You may have the wrong plunger or it's worn or damaged.. Without seeing it, I can't say.. When I build a Q-jet, I put the plunger and metering rods in before the gasket goes on.. There is a plastic ring at the top of the plunger just below the rod hanger.. With the plunger removed from it's bore, this plastic piece just flops around.. Drop the spring in, and install the plunger with the rods attached.. Then press on the hanger to shove the plunger to the bottom. Using a small screw driver, gently push the plastic piece into the bore until it's even with the top of the bore.. It should fit tight enough to hold the plunger in place.. The plunger should move up and down freely when finger pressure is applied to the top of the hanger.. The gasket fits around all this but none of it touches the hanger or rods..

We're zeroed in on the carburetor, but I honestly believe your problem lies elsewhere... If stuff has been bent, modified, exchanged with other parts, fabricated, or otherwise jacked with, I'd suggest you discard the carburetor and get another one..

Yes... I read it... But the carb is currently together and I can't get to doing all this while it is on the truck... His way was to just stick a screwdriver down the fuel bowl vent and if you can push it down and it springs back up, its doing its job... Anyway RustyPile, can we agree this is a very likely culprit to my hesitation issues?

 

[RustyPile]

I won't agree with anything you say since you've jacked with that carb so much.. What I do have issue with is you coming on here seeking help and not following the instructions and information given.. And then coming back here and calling out me or anyone else, pointing out something you found ELSEWHERE as if it's brand new information and/or contradictory to what you've been told by me/us, when that very same information was given to you previously RIGHT HERE..

 

[3504boltmain]

I won't agree with anything you say since you've jacked with that carb so much.. What I do have issue with is you coming on here seeking help and not following the instructions and information given.. And then coming back here and calling out me or anyone else, pointing out something you found ELSEWHERE as if it's brand new information and/or contradictory to what you've been told by me/us, when that very same information was given to you previously RIGHT HERE..

My mistake, maybe I didn't read what you posted correctly. There was A lot of information in there. I will reread and post back. I'm not trying to bash. I'm trying to solve a problem I have with this truck. All things that I jacked with on the carb, I put back. I have been digging for information on this type of hesitation for over a year now... So, I'm sorry if my reply seemed to lack regard to what you've been helping/ informing me about all along.

 

[RustyPile]

<...........snip.........> I'm sorry if my reply seemed to lack regard to what you've been helping/ informing me about all along.

Apology accepted..

 

[Honky Kong jr]

 

[3504boltmain]

So I assume the next step is to pull the carb out and apart. In my defense, I had never ripped a carb apart before, and I wasn't sure weather the accelerator pump or the power piston should have held themselves down in their bores when reinstalling the air horn... I didn't know that little tidbit until today to be honest (even with information presented to me before). The fact is that I don't know for sure that you can push the power piston down inside the vent tube and it should spring back up... What we read on the internet is always true right? If, by what you were telling me in post 103 explains that in any way... I'm missing that fact all together in all honesty. The reason why I didn't point out the fact that The power piston and acc. pump operated funny during installation of the air horn was because I completely forgot about the fact until the posts prior to your 103.
Side note: The Power piston slid up and down in it's bore properly when the air horn was off.

 

[3504boltmain]

the plastic piece serves a dual purpose.. It holds the plunger in place and it is also a stop that prevents the plunger from rising too high.. Since the metering rods are tapered, the higher they rise, the more of the jet orifice is exposed to fuel.. It allows more fuel to flow. If the power valve/plunger is properly installed, and none of it's components are worn out or missing, you don't have to hold it in place while installing the air horn -- the little plastic piece holds all that in place..

Found it....
I even replied "hmmmm...." to this one too.... totally missed the "It holds the plunger in place...." part. Or I assumed that I held it down well enough and it should be ok... and disregarded this important little piece of info.

 

[Dougnsalem]

Here ya go...

http://garage.grumpysperformance.com/index.php?threads/q-jet-info.1144/

Not meaning to interrupt your OT discussion (it has been pretty funny).... However, man that was one kick ass link. The amount of info there is just insane. Cool stuff...
Thanks much!

Hey @3504boltmain , if you scroll WAY, WAY down, the dude walks you through step by step on setting/checking everything on the Quadrapuke. Just me, but I'd get a Holley.... Lol.

(And check the cam)

 

[3504boltmain]

Not meaning to interrupt your OT discussion (it has been pretty funny).... However, man that was one kick ass link. The amount of info there is just insane. Cool stuff...
Thanks much!

Hey @3504boltmain , if you scroll WAY, WAY down, the dude walks you through step by step on setting/checking everything on the Quadrapuke. Just me, but I'd get a Holley.... Lol.

(And check the cam)

Yeah man, I checked it out to... Nice write up there... this truck is dead, and I've got the point about the cam... I cant afford tools or parts right now, so nothing is getting done. I did manage to play with a thermal gun... looks like one o f the cylinders is colder than the rest, and one is hotter... I know ima get slammed for doing so and posting this. But wth, back yard mechanic i am i guess... Hopefully i start making more money very soon... when i do, I'm replacing my ignition components, it that doesn't fix it, I'm pulling the engine, trans and axle and crushing the truck.

 

[Honky Kong jr]

Yeah man, I checked it out to... Nice write up there... this truck is dead, and I've got the point about the cam... I cant afford tools or parts right now, so nothing is getting done. I did manage to play with a thermal gun... looks like one o f the cylinders is colder than the rest, and one is hotter... I know ima get slammed for doing so and posting this. But wth, back yard mechanic i am i guess... Hopefully i start making more money very soon... when i do, I'm replacing my ignition components, it that doesn't fix it, I'm pulling the engine, trans and axle and crushing the truck.

I haul truck away!!!!

 

[Dougnsalem]

Yeah man, I checked it out to... Nice write up there... this truck is dead, and I've got the point about the cam... I cant afford tools or parts right now, so nothing is getting done. I did manage to play with a thermal gun... looks like one o f the cylinders is colder than the rest, and one is hotter... I know ima get slammed for doing so and posting this. But wth, back yard mechanic i am i guess... Hopefully i start making more money very soon... when i do, I'm replacing my ignition components, it that doesn't fix it, I'm pulling the engine, trans and axle and crushing the truck.

Nothing wrong with being a back yard mechanic. I know a couple damn good ones. Plus, if you aren't doing it every day as a career, you may enjoy it more as a hobby than I would. 30+ years of it takes its toll.... Lol I'm on hold for the moment, until the cash flow gets fixed too. It will though. That stuff always works itself out sooner or later....

So don't crush the truck!!! Lol

EDIT:
And don't give it to Hokie Kong either! Lol