Quadrajet four barrels don't open.

[vince1]

Ok, what has to happen? I know the choke has to be open. Not running I open the throttle all the way and the linkage to the throttle shaft seems OK. I have never seen the plates up top open. Which port does the vacuum line to the (choke?) pot go to and when does the vacuum come on? I would suspect at full throttle??

edit: The 79 C10 engine is in a 66 C10.

[vince1]

At idle the pot lever pulls back preventing those top secondary plates to open. The line goes to the port coming out at an angle from close to the top of the carb which is close to the fuel inlet line. Is that correct?
The engine runs like crap and I can't throttle it down low enough with the throttle linkage stop screw. How could I test for a vacuum leak?
My heart is not in this. If I had played with these SBC's when I was a kid I suppose this would be easy now.

[geezer#99]

Post some pics of your carb.

[truckin 79]

Well it does sound like something is going on with carb. When truck reaches normal operating temperature and choke is all the way open. Well first make sure choke butterfly opens all the way. Then place your hand over carb mouth lightly and if it idles up higher then it is running lean and probably a vacuum leak. You could also check to see if exhaust smells like gas or check spark plugs as well. You could also just look at rubber lines and look for cracked or brittle vacuum lines.
The opening of the secondaries would not affect at idle only wide open throttle. It takes a plethora or things for secondaries to open. The choke has to open fully and that should keep secondary lock out tang pulled back, then the primary choke pull off needs to have good vacuum and then the secondary choke pull off needs good vacuum as well. I have always disliked quadrajet secondary opening is basically mashing gas pedal all the way to the ground to make it kick in.

[Dead Parrot]

If it has power brakes, a leaking booster can be a source of vacuum leak. I know from experience that a booster can leak enough to mess up idle while still providing enough boost to make you think it is fine.

2nd the picture thought. There are many variations of Q-jets.

[Bandit130]

The way I test for vacuum leak is to start a cold engine, spray carburetor cleaner all around where there are vacuum lines and around carb and brake booster. When the RPM's change, that is where the leak is.

DO NOT SPRAY ON A HOT ENGINE.

There are other ways, but for me this is quick and easy.

Good Luck!

[vince1]

click to see full imges

Hose above fuel inlet goes to the vacuum pot.
Hose down low to right of picture goes to distributor.

[kwmech]

Very rarely will you see the upper flaps open while you rev the engine without a load on it. Spring tension on the flaps can be adjusted by loosening the set screw and adjusting the spring tension with a small screw driver

[vince1]

I rarely use the truck.

Last time was a haul to the dump. Before that was hauling about a 3/4 yard of cold mix asphalt. Of course I protected the box with a $10 sheet of OSB. Before that was hauling some 16' lumber. You don't see the idiot trucks of today being able to do that. I get thumbs up and comments every time I go out.

Still the running rough and excessive fuel consumption seems recent. I'll have to spend more time looking at it. It won't fix itself.

[geezer#99]

By the amount of shiny gas stains at the accelerator pump, I’d say you’re flooding. Floats too high or needle/seat not sealing.
The hose you have for the choke pull off can be hooked like you have it, but there should be a port at the back down low on the carb base to use. Possible vacuum leak if it’s not capped.

[vince1]

Thanks guys. I will figure it out.
It was starving when going up hill under power and that was OK after I changed the carb fuel filter. Could that have changed anything? It seems like my problem may have started right after that.

[vince1]

I think geezer has it. I will change the hose to where he says it should go and look into the flooding.

When I changed the filter a couple of weeks ago I could not blow through it but there was no dirt inside. Anyway it burned a lot of fuel last trip so I agree the float needle must be stuck open.

I'll also get a can of carb cleaner and check for vacuum leaks. The two long bolts at the front holding the carb down were slightly loose but not enough to make a difference. I got about a quarter turn on them.

[Bandit130]

If you rarely drive it and your fuel has ethanol, you probably need an additive for the ethanol. Also sounds like it is time for rebuild.

[Dead Parrot]

Getting a small bit of dust/dirt/bug into the filter housing during a change is fairly common. If things go well, it passes through without issue. But sometimes, it will stick in the needle/seat area and cause flooding.

Engine off. Might try hand operating the throttle until the accel pump quits squirting. Let it sit for a bit before starting. If there is some crud in the needle/seat, Full gas flow with the needle full open might clear it.

Some of those hoses look old. Fresh hoses with fresh plugs might fix a vacuum leak. Possible one got moved and cracked during the filter change.

[Loco83]

Wouldn't hurst to give that Qjet a good spraying with GUMOUT carb spray cleaner.

[vince1]

I looked at it today and found a few things wrong.

1) That little pipe down low at the back of the carb coming out at an angle had nothing on it. I moved the vacuum pot hose to it and blocked the other one.
2) The coiled spring on the secondary throttle shaft was just sitting loose. I pulled the tab under its designated hook.
3) The throttle linkage is not correct and does not rotate the main shaft far enough. I will have to modify it to work properly.
4) The plugs are black and it is obviously burning rich. Maybe I'll have to go over the carb again, check float level, smaller jets perhaps and finally bush the throttle shafts as they are somewhat worn. New 2 barrel carb and manifold?
5) I pulled some plug wires and when I got to #5 I did not hear much of a difference in sound from the engine but immediately heard the wire sparking somewhere to ground, probably back at the distributor. I swapped #3 plug with #5 and no difference detected. I don't think it misses under load but I will definitely have to look into that, maybe get a new distributor cap.

Edit: It's actually running pretty good again, no more sticking float.

[GSP7]

Get Cliff Ruggles Qjet book. He sells best rebuild kit, call him or he has a parts and forum web site

Read It, study it, until your head spins. Then you might wanna get a holley or a Edelbrock

That looks like a good year carb. Looks like Calif emission carb... What is the carb #

[vince1]

Where is the carb #? I don't think I'll look for a while until the air cleaner comes off because it is running good again. Maybe it was the rap on the side of the carb that did it. I will change the pivot point on the carb to coincide better with the 66 linkage. There is a hole further down closer to the throttle shaft that will give better response and I will modify a bolt to put in there.
Electrical tune up kit is also on the agenda.
Thanks for the tip on the book.