carb issues (vacuum ports & linkage)

[Archangel]

AC Delco R45t or R45ts is typical depending on the head. Pull one of the existing plugs and cross it over. I forget which is which, but one of those plugs is a long reach with some goofy long threads on it, the other has short threads. I also have run NGK plugs in Chevy motors with no complaints, and right now my truck has Autolites because the parts store had either cheapo Autolite, Bosch platinum which I determined to run poorly in this motor, or some expensive double platinum $6 per plug AC Delco thing.

My engine has Autolites too apparently, just pulled #1 and it came out quite easily (quite surprising actually). I'll get some AC Delco R45 plugs tonight or tomorrow.

[Archangel]

You could just bring the carb if you want. Used to have a couple of them around here from boats. That big flapper is the air valve for the secondars not a choke. The little vacuum can with the short hose keeps the air valve closed when the choke is on.

The big issue with those caarbs is if some little cup plugs start leaking inside the carb. Other than that there fairly fool proof. Rebuild kits are fairly cheep if you want to go that route.

Well, that would be the logical thing to think of, wouldn't it. Ya, in that case I'll just bring you the carb itself, and you can check for those cup plugs that are known to leak or any other problems as well. By the way, I started the engine about an hour ago, had the carb and the heads drowned in carb cleaner and wanted all of it burnt away before I do an oil change, surprisingly even with all the vacuum ports open the truck fired up right away and also held a nice idle of about 800rpm - guess getting rid of the choke flapper and washing and lubricating all the linkage joints and springs actually made a difference.

Post 4 blue circle not shure of what your circling but I think you have circled the rear barrel metering rods and linkage it lifts the rods out of the main jets when the air valve opens.

Yep, the circle in that pic shows something connected to the flapper (air valve), so it must be the metering rods linkage, Okay, in that case, if the air valve is what is causing those to move, what is causing the air valve to move? There's nothing attached to its shaft, except for the vac solenoid and the metering rods linkage, absolutely nothing else...

[turbo2256b]

Air valve movement is a mistery. I I rember corectly air pressure throttle in the rear opens below the air valve pulls the air valve open which has an adjustable tension alen head screw on the same side as the vacume canester with the little hose. Located on the end of the throttle shaft.

[Archangel]

Air valve movement is a mistery. I I rember corectly air pressure throttle in the rear opens below the air valve pulls the air valve open which has an adjustable tension alen head screw on the same side as the vacume canester with the little hose. Located on the end of the throttle shaft.

Hmm, I admit I never even thought of that - of course they can use the engine's vacuum to suck the valves open, it's actually a pretty darn good idea. Okay, that makes me feel better now, so the only thing missing from my carb is the choke - you got some Q-Jet vacuum chokes laying around?

[gadget73]

Yeah, the air door is vacuum operated. There is a mechanical part for the rear throttle plates, but unless that air door opens, the metering rods are shut and no fuel flows back there. Not sure how to adjust them, but its similar in theory to the old Thermoquad carb. The TQ had an adjustment spring to determine exactly when the air door opens. I think the QJ has some other spring involved but I honestly don't remember where.

[Archangel]

Yeah, the air door is vacuum operated. There is a mechanical part for the rear throttle plates, but unless that air door opens, the metering rods are shut and no fuel flows back there. Not sure how to adjust them, but its similar in theory to the old Thermoquad carb. The TQ had an adjustment spring to determine exactly when the air door opens. I think the QJ has some other spring involved but I honestly don't remember where.

Well one of the guys over at FSC gave me a link to a website that has shitload of info on the Q-Jet carbs, so I'm sure I can find all about it, I just need the time to sit down and read couple hundred pages of manuals

[gadget73]

Really once you get to looking at how they work, its not too complicated. Its just been a year and a half since I even saw one, so my memory is a little foggy. I've rebuilt plenty, and pieced a few together out of the box of dead carbs for people, and amazingly most of them ran well.

[turbo2256b]

Hmm, I admit I never even thought of that - of course they can use the engine's vacuum to suck the valves open, it's actually a pretty darn good idea. Okay, that makes me feel better now, so the only thing missing from my carb is the choke - you got some Q-Jet vacuum chokes laying around?

SORRY THE ADJUSTMENT IS LOCATED ON THE AIR VALVE SHAFT.

[marquisman]

we only run NGK in in the boats we sevice, and seem to be the best plug.

[turbo2256b]

Doubt that I have a choke around. Never use them

[gadget73]

Most of the motors I worked on had heat chokes in the manifold. Half of them were bad and just fixed to wide open. Mostly they're useless unless you need the high idle to keep it running at first.

[Archangel]

OK then, no choke it is, although truck can definitely use it - got my new VC gaskets today, replaced 5 plugs (cause of the headers the other 3 need a box wrench I did not have) with new AC Delcos, fired it up, and first time I took my foot of the gas it died, when I let it warm up it idled fine. I've adjusted it to idle at about 1000rpms which is pretty high, but that's the only way it also idles in gear. When shifted from Park or Neutral to Drive the whole truck twists from the clutches engaging in the tranny, and reverse almost spins the wheels - engine has some balls for sure. I drove it around the apartment complex streets, it was fine except for the fact manual brakes suck big time, and also the funky noise that scared the previous owner. When I pulled back in my carport I noticed a pretty bad oil leak again, this time on the passenger side - apart from the carburator the only things I've tinkered with were the valve covers, so I'm prety sure the passenger one leaks from the rear inboard side. Which is not such an issue, as I already have some M/T aluminum VCs on order from ebay, ran me $32 with the shipping - I'm gonna wait for those to come, then deal with the oil leak. Also there is some awful valvetrain noise from under the driver side VC, but I never set the valve lash, so I guess I'll have to do it during the VCs swap. Will see how the whole thing goes, but I can definitely say the engine is worthy getting fixed up

[gadget73]

Is your QJ an electric choke or a mechanical heat choke on the manifold? You can always just run a manual choke if its being bitchy in the cold. Boats dont have much of a problem with no choke because the throttle can be set wherever. They dont have high idle cams.

[Archangel]

Eh, I might not have a high idle cam either, as a matter of fact I have no clue as to what's inside the engine - I know it's been rebuilt, and that it has a "mild" cam (which may explain the unwillingness to idle low), but that's about where it all ends. How do I know if it was an electric or hot-water choke?

[gadget73]

A high idle cam is on the side of the carb, its an eccentric thing the idle stop rests on to keep the throttle open more so it warms up faster. Electric chokes would have had wiring, and a round black plastic disc on the side. Usually you'd see where it would mount. Heat stove ones have nothing on the carb, just a spot for the linkage to hook.


Thats a remote choke type


is what looks like a heat riser type choke. Electric chokes look extremely similar but have a wire terminal


thats the remote heat choke. That thing screws to the intake manifold.