I've just arrived in Colorado with the '67, and my Q-Jet is doing something new. After driving at freeway speeds, my idle is staying high (~2500 RPM) when I'm off the throttle. After shutting off the engine for a few minutes, the idle speed returns to normal. The throttle linkage to the accelerator pedal is not sticking, nor is the primary shaft. The power piston is staying down while the high-idle condition is happening. I do notice some fuel out of the top towards the secondary bores, which means the bowl fuel level is high. I believe my float may be stuck low. The carb is a re-built factory 4MV core for 1967: carb number 7027241 which I re-built about 2 years ago: http://www.v8buick.com/showthread.php?242604-Q-Jet-Quartet&p=1982826#post1982826 This would be number 4 from that thread. I've used it for 2 years with zero trouble until now. It has all of Cliff's new parts in it: idle tubes, bronze primary shaft bushings, new blue ethanol-resistant pump cup, new large float, .125 seat with new needle, 73 primary jets and 37 rods. I installed custom screw-in primary well plugs with Marine-Tex, so I do not think they are leaking. If they were leaking, the high idle would stay high and the bowl would drain empty...which it is not. I think all that hauling ass across Nevada/Utah/Wyoming has gotten my float to start sticking down. I took off the top of the carb in the hotel parking lot, and checked the float. Looked okay, but I know that can be deceiving. The bowl was 1/2 full of fuel. No gunk visible in the bottom of the bowl. Power piston okay. Metering rods okay. Pump okay. I took out the float and needle..didn't see any gunk on the tip. I used a small screwdriver wrapped in a gas-soaked rag to clean any carbon out of the power piston bore. I re-installed the rods and power piston, and checked the spring tension. Worked fine. I wiped down the float with the gas-rag, re-installed it, and bent the tang to make it about 1/16" lower. I noticed if I pushed it all the way down, it would occasionally stick...but I thought the added force from the needle would compensate. I put it all back together, and started the engine. Purred like a kitten. Drove it around town. Seemed fine. I let it sit for an hour, and took it around town again. Once my engine shifted into second, I noticed my idle go up again. It stayed up. I parked it. Idle was still high. Checked power piston: it was down. Shut it off. Waited a few minutes. Started it back up. It idled normally. I think cleaning everything helped...but maybe my float is fouled with fuel and is too heavy. The high-idle seems a little lower than before. How long do floats normally last? I've been using it for about 2 years....maybe that's their shelf life. This new gas may be screwing things up in more ways than one.
Len, The float level generally doesn't have an effect on the faster idle. I would check: 1. make sure your choke is completely disengaging and letting the fast idle cam release. 2. Make sure your secondary air valves are closing all the way and aren't sticking just before they close. 3. make sure your secondary throttle blades are closing all the way and aren't sticking. #2 is the most common, and is not easy to notice. Many times they hang up about 1/8" before complete close, and this lets in air and lifts the secondary rods. If you got your parts from Cliff, you should be fine on all of those. I wouldn't be thinking parts issues at this point.
I just checked it after letting it sit about 40 minutes. Started it up, and idle was high. Bleeped the throttle a few times, and after about 1 minute, the idle returned to normal. During the high-idle, the secondary air-doors were slightly open, but pushing them closed didn't seem to lower the idle at all. Maybe there is something hanging up on the passenger side of the carb. The fast-idle cam was all the way down, but maybe some teeth on the follower are hanging up and keeping the throttle plates open even when the throttle is totally off. I'd adjusted the fast-idle a bit tighter a few days before I left on the trip so that it would stay on longer when the engine was cold. I'll try adjusting it some more in the other direction, and see if the problem goes away.
Carman, I think you're onto something with the secondary air doors being open a little bit. If the secondary throttle plates were closed, the air doors above them wouldn't be getting sucked open. Something must be keeping them open a bit, and it's allowing manifold vacuum to pull open the air doors & lift the rods. I'll take another look after the thundershower passes...it just started raining in CO.
Carman is *the* man. Looks like my secondary throttle plates are staying open a touch, and that's what's causing the high idle. I was able to push them open by hand a bit (on the throttle linkage tang) while the engine was idling, and they stayed open. Idle was high. Pushed them the other way: idle was normal. The secondary return spring is either weak or dirty. I gotta get me some solvent & clean it up. All across the countryside, I was staying on the primaries, and barely hitting the secondaries unless I hit a steep hill or had to pass someone in a hurry. All that dusty territory has my spring all dirty, and the secondaries are getting stuck open. Thanks for the help!!! :Smarty:
Update: the issue is fixed. My secondary throttle shaft spring was all gummed up & coated with 5 states worth of highway dust. A few shots of carb cleaner later, and presto: I have my spring tension returned. I can snap the secondary tang and the shaft returns to fully closed every time. Next long trip I take, I will be sure to keep these springs clean!!!
Great news Len!! Those things just get a little sticky sometimes. Glad you figured it out. Those little things like that are always frustrating.
Back from CO, my Buick took 3rd place in the modded class. My secondaries started to stick again, even though the spring was clean. Turns out the rod connecting the primary shaft to the secondary tang was hanging up in the slot. I changed the rod out to a shiny new one with fresh cad plating, and adjusted it for the proper slack. Problem seems to be all gone now (fingers crossed).
Any pics of the piece that you think was sticking. I have a brand new 72QJ with divorced choke and idling at like 1500rpm and cannot for the life of me figure out what's going on. I have done all the obvious stuff already. Where is this "the rod connecting the primary shaft to the secondary tang"?
This is the secondary throttle rod: http://quadrajetparts.com/rochester...her-linkage-secondary-throttle-rod-p-312.html The part with the clip connects to the primary shaft. The other end loops through an oval hole in the secondary shaft, and the end of the rod pushes against a tang at the top of the secondary shaft linkage. Over time, the sharp edges of that oval hole will wear a groove into the rod and make it stick. When it sticks, the secondary shaft won't return to the full-closed position at idle. That is what makes the idle jump up to 1500 RPM or more. If it happens again, try pushing your secondary shaft closed by hand.
just a tip: an ez way to check for this secondary throttle sticking open condition is to get the engine running and at the high idle. manually open the secondary air flaps with your hand. This should bog the engine down and possibly out. If the secondary throttle blades are sticking open. If there is no change when you open the air flaps then the secondary blades are not sticking open.
I'll try to look at it this weekend. Several people seem to believe something is getting hung up on my choke linkages because upon initial start and warmup, the first punch of the throttle brings RPM down, if you touch the gas a second time (I'm talking with the engine fully warmed up now) the idle flies up and stays up. Also, I am thinking my distributor might be whacked a little. Wondering if my weights are intermittently getting hung up or if springs are weaking.
