Good morning guys. I’m having some minor tuning issues with my quadrajet. Car is definitely rich at idle and it has a bad bog at wot. I am a mechanic but have no experience with carburetor tuning. Anyone near Pittsburgh that could help me get this thing dialed in on the car? I would be glad to pay for your time.
Not anything you can't figure out yourself! What do you have the mixture screws set to? Do you have a wideband? What's the vacuum reading? As far as a bog, check the secondary air flaps to make sure they're not just flopping open. They should have some resistance
If the primary throttle blades are open too much, you'll get nozzle drip. That's when the engine idles on the main nozzles, and not the idle system. Symptoms include extremely rich idle, no response to the idle mixture needles, and hesitation from a stop. A bog when transitioning from primary to secondary operation usually has to do with not enough damping of the secondary air valves. There is a spring wind up adjustment for the air valves. In addition, the primary vacuum break should be holding the air valves closed at idle. With the car idling, make sure that primary break is working, and the long link is keeping the air valves closed. Between those 2, they should keep the air valves from flopping in with secondary throttle valves wide open.
I appreciate the response. You guys are speaking French to me, sorry. I am sure I could do some research and understand what you guys are asking/telling me. I was talking to a local carb “expert” and he is suggesting that since my engine is a little “cammed up” I more than likely had to increase the idle speed, which is correct. He is saying that the increases idle speed is bypassing the idle circuit and using the primarys as you stated Larry. He is suggesting some internal carburetor modifications I think? Thing is Ken built this carb for me so wouldn’t he have done that?
If you gave all the specs to Ken, yes, the carburetor should work. What you need to do is close the throttle blades more. Bigger cams like more initial timing. That means reducing the mechanical timing so the total isn't too much. If you want to experiment, temporarily advance the timing to at least 20*, at idle. Then back out the idle screw to close the blades. Then play with the idle mixture screws. Turn them in one at a time and see if they have an effect on idle quality. If you can set the carburetor up that way, you'll know how to have your distributor recurved. Don't drive the car that way as it will over advance at higher RPM. If only it was that easy.
Larry's suggestion is spot on, come to find 90% of carb probems are ignition related. Also remember, problem with cammed cars is the best builder can only guess how the car will react with YOUR cam, it often takes 2-3 tries to dial in the amount of idle air bypass and subsequent air/fuel ratios (and mine took more than that, and I know what I'm doing). Once youre run through Larry's advice, if you still have an issue give Ken a call and if you can take the carb off the car by yourself, he can walk you through the process of fine tuning.
I appreciate your comments, I did some online research and made some simple adjustments. I set the air screws with a vacuum gauge, i noticed that they made maximum vacuum at about one and a half turns out, after that the vacuum reading didn’t really change so that’s where I set them, I also set the choke and high idle. As you guys mentioned it is dripping out the primaries at idle, I turned the idle down to where that stopped and test drove the car, it was just too low, kept stalling out on me so I had to turn it back up. Is there any way to fix this with adjustment or does in need internal modifications? Also I didn’t notice the bog at wot on my test drive, could the air screw adjustments have affected that?
I have a HEI distributor that I plan on installing this season so I’ll play with the timing as you suggest when I install it. You state that I need more initial timing and need to limit advance so do I need to buy a kit with those bushings or stops that limit the advance weights travel? What kind of initial timing numbers should I be targeting? Or how do I know what initial timing MY motor likes?
There are no bushings for the Big Cap GM HEI. I believe there are weight kits including the center piece that limit the mechanical advance. You can also completely lock out the mechanical advance so you can run constant timing. An easy, reversible way to do this is the make a metal strap with holes that fit over the weight pins, and hold the advance mechanism in a full advance position. The only problem with locked out timing is the engine will not want to crank when hot. The way around that is with a crank retard like the one select able on some ignition boxes, or as an add on to your ignition system. The weight kit I referenced is somewhere in the Power Timing thread. In general, a bigger cam will want anywhere from 12-20* of initial advance. That means limiting your mechanical advance to 12-22* depending on the initial advance, and how much total advance you want to run. In any case, you can simple advance the timing at idle enough so you can close the throttle blades and get your idle mixture screws to be responsive. You just don't want to drive the car like that as it would over advance at higher RPM, but it would be a good experiment to see if you could get the carburetor to behave at idle. There is quite a bit of discussion on modifying the HEI advance curve in the Power Timing thread, https://www.v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/ (start at post #28)
Make sure float level is correct first. When carbs get shipped they get bounced around with nothing to dampen the float. Seen people buy high dollar Holleys from custom builders and then complain that doesn't run right. Then I ask "did you check the float level?" and they say "no why should I? I paid $$$$, it better be right?" Oh well.......
Man I didn’t really focus on the number, I was just watching the gauge until it stopped rising. I did have to increase idle rpm though to get the needle to stay steady and in the green before I made any adjustments, was that ok to do? I wanna say vacuum was around 20 inches but again that was with increased idle speed. When she was idling at normal speed the gauge was in the red and needle bouncing all around.
20" Hg at idle is normal for a completely stock engine. An engine with a moderate cam will be 5-7" LOWER, but it should be steady. I agree with Jason, a bouncing needle, that's a problem. https://www.classiccarrestorationclub.com/video/engine-vacuum-troubleshooting/
Oh boy, thanks you guys. A couple things I noticed on the attachment. They are saying to use a port on the intake, I was plugged into the big port on front of the carb, is that ok? I had a cheap gauge so before I get nervous I’m going to invest in a better gauge. I wasn’t fully up to operating temperature and it stated that I should be. The article didn’t say anything about what rpm you should be checking at? I mean as I throttle up it steadys right out, what does that tell you? If it was a mechanical issue I wouldn’t think rpm increases would fix it?
Manifold Vacuum is Manifold vacuum, doesn't matter where it comes from, carburetor, or intake. Yes, full operating temperature, Idle RPM out of gear should be roughly 900-1000 RPM. Vacuum should be steady. This is a video of my engine idling. I have a vacuum gauge in my engine compartment. That's a solid 15" HG, and the reading is steady.
