Ok guys the secondaries on my new carb aren't opening. There is a lever on the passenger side of the carb that is suppose to get knocked out of the way when the throttle opens so the secondaries can open but it isn't moving enough. So the bar on the secondaries gets caught and wont allow them to open at all. How do I adjust the bar where it will get out of the way? By the way its an 800 Q-jet. Thanks in advance. C.J.
Secondaries Your secondary throttle blades ARE opening - they are mechanical on a Q-jet and open with a progressive linkage. What may not be opening is the secondary air valve. This is the flap you can see on the top of the carb, and it opens under engine vacuum and also raises the secondary metering rods to allow fuel into the engine. Is your choke hooked up? Is the fast idle working? There is a lockout that keeps the secondary air valve closed until the choke opens. If your choke is not opening the air valve won't open either. Also, the air valve is modulated by the vacuum break on the passenger's side of the carb. This is a small vacuum diagphram that holds in with manifold vacuum. It releases slowly when vacuum drops and allows the secondaries to open. The air valve on a Q-jet will often not open when the car is stopped, you have the hood open, and you wing the throttle. The valve only opens when the engine is under load and needs more air, creating a vacuum under the air valve so it gets "sucked" open. There is a small spring that is adjustable to tune the amount of vacuum required to open the air valve. I suggest that you go to Amazon and buy Doug Roe's book on Rochester carbs - it costs less than $15 and will give you all the right info on your carb.
I realize that the air valves on the top won't open unless the car is running because it requires vacuum to open them. But the mechanical valves aren't opening either because of some kind of stop mechanism on the passenger side of the carb. I guess its there for safety reasons but i'm not sure what it does. All i know is it is stopping the secondaries from opening. My old Q-jet didn't even have one on it. It was a 69 and the one on it now is a 73 i think. I could probably just cut the thing off and it wouldn't make any difference. I just wanted to see if there was a way of adjusting it. I can't find one. The little lever i'm talking about was designed to stop them from opening but i'm not sure why. Its just not getting hit enough out of the way for the secondaries to open.
It locks the sec. out until engine is warm/choke open. The fast idle cam kicks it out of the way when its off fast idle. Some carbs have a pin on the choke that kicks it out of the way. It's to keep it from bogging when the engine is cold. I took mine off. I'm smart enough not to nail it with cold oil anyway. Just loosen the screw holding the choke mech to the body enough to pull it out. If you pull the choke out too far you might drop the linkage in the carb. Not the end of the world, just a little more work. Have fun!!
Sorry guys i don't know a whole lot about these carbs but i'm trying to learn. Ok i went and looked at it and i don't really see how its gonna fix itself at it warms up but i'll take your word on it. Now let me ask you another question. I just bought the carb and put it on. I started it up and it ran fine but its idling very fast. And the idle adjustment screw is all the way out so is there another idle adjustment somewhere i'm not aware of? You said something about fast idle and a fast idle cam. So is that why its idling so fast, because its cold? The old carb never did that when i started it cold. Please help me understand all of this.
Ok, i just went out and played with it again. Started it up, its still idling too high so i tryed to tap the foot petal but that didn't idle it down instead it just revved higher like the throttle was stuck, but the throttle isn't stuck, i checked it. Whats the deal? After I tapped the pedal it did rev back down just very slowly but its still Idling way too high. How do I get this thing adjusted out where it will run smoothly and not redline on startup?
Does it slow down when you push the fast idle cam down??? fast idle cam is on the choke side of carb. It's a lever looking thing that comes out about flush with the front of the carb. Not really a lever, it really is a weight. Did you let the engine warm up??? Is the choke hooked up??? Is it a devorsed choke or is the choke coil mounted on the carb??? It may just need an adjustment if its fully warm and the choke still closed or on fast idle. Let me know, I use to build 3-5 q-jet's a week before FI took over. I don't have my camara here or I would take some pic's for you. I have to get back to work, I'll try to check on this later.
Not the greatest pic, but it does show where the fast idle cam is located. It should move freely on a warm engine. Right under it is the fast idle adj. screw.
Well the secondaries opened up after the engine got warm as you said it would. Don't know exactly how or why but it did and thats all that counts. And I found the idling problem today and feel like a real idiot for not realizing it before posting but thats the way it goes. There was a "thingamabob" mounted on the intake manifold. Emissions something maybe? I really have no idea. it was screwed to a bracket on the intake. It looks like a saucer with a screw running through it and a spring on the other side. On the stock carb it sat flush with the throttle lever on the drivers side of the carb, but the lever on the new carb was bigger so it was holding the throttle partly open. So i just took the thingamabob off and it fixed the problem. It Idles great, runs good and has good power. After all the warnings about getting "parts store carbs" i was kinda nervous about buying one but now i'm glad I did. Besides it was rebuilt by Holley so I don't know why it wouldn't be built right. As far as i'm concerned it beats the hell out of paying $450 for a new one.
Is the saucer thing you have on your car the gold looking thing on the back of this engine in the picture? Sounds like what you ware describing is a cruise control unit. It has a chain that attaches to the throttle linkage on the carb via a ball joint.
No the thing i'm talking about is quite a bit smaller and should be mounted right under the snorkel in that picture. I'm not sure but that might be a piece of it peaking out but i really can't tell with the snorkel in the way.
Anti-stall dashpot. When the engine rapidly goes to idle, it slows the throttle down the last little bit to keep it from stalling. A sudden surge of engine vacuum on decel causing it to to go rich for a second, causing high HC out tailpipe and sometimes engine stall. Now you know more than you need too.
Well alright then. Thanks for the bit of info. I appreciate all the help guys. thanks a lot. C.J. Myers
