Another source of vacuum leaks are the hoses, switches and diaphragms that make up the hvac system. On my car taken individually they weren't a big deal but having multiple tiny leaks caused a problem.
Thanks for the tips. I checked the other vac lines by plugging them off. I actually disconnected the HVAC system vacuum long ago since the previous owner ripped out half of the a/c stuff anyways. I know for a fact the HVAC vacuum did have a leak, as when I first bought the car and didn't know any better, I remember there being a hiss under the dash! I ordered two new .25" gaskets from Greg @ Quadrajetparts.com and already have them on. Time to test it out tomorrow. Hopefully there will be a little more improvement.
Ugh gaskets are on. Tested for leaks and the new ones are sealed. Still showing the same vacuum though.
Your going to have to re-adjust your idle and stuff. I suppose a good time to check something was with the carb off....the relationship between the throttle blades and the idle x-fer slots. Anyways, you can back the idle all the way down and start over, using your vacuum gauge. Helps to have a helper to hold the brake in "R" as you get it close.
Hey gents, I verified that my damper is indeed indicating accurate TDC. I used a piston stop and then made the two marks on the balancer and found the middle. It was right on top of the factory scribe on the balancer! That being said, my timing should be set right. I did a little light reading on the Q-Jet throttle blade vs idle transfer circuit issue. We could be one to something here, but the service manual doesn't provide any sort of spec that I can find for how open the blades should be. Is there a correct way to set this up? Edit: I read elsewhere that if you remove the carb as it is set up right now, and look underneath, the throttle blade should only no more than a 'small square' cross section of the transfer slot. Is that about right? I also now understand what WE1 was mentioning earlier about the vacuum being too low to to hold down the power piston. I read about a test you can do with a straw to see how far the piston moves down with the engine off so you can see if that vacuum is holding it down all the way at idle. I will give that a shot too. I suppose the wrong gasket could be an issue as well, but I bought the 4-hole 1703 from quadrajetparts.com, so I can't imagine I have the wrong ones for a 1976 Qjet...
14" vacuum should hold most power piston springs down, but I'm no expert on that. Shouldn't have any fuel flowing from the main circuit until the throttle blades open further. You don't really need to remove the carb to see the gap on the blades/bore. Simply back off the idle all the way and start over, just give it a little bit of opening and go from there. Pulling fuel from the off-idle transfer slots sucks to try to tune out, you almost have to close off the idle mix screws to do it. There's also more rpm drop in gear with that condition (throttle too far open at idle). Jim is 110% correct about the timing drifting around at idle and with too light of distributor springs. I keep some spring stock from the hardware store and bend them up as needed (mostly to save delays due to shipping and having to keep every kit on the shelves). Service manuals don't cover a lot of common sense issues or really any from a performance/modifications standpoint. This is where forums shine You don't have to spend your whole life figuring this stuff out.
I have used a small thin bladed screwdriver, and inserted it into the bowl vent. If you angle it toward the front of the carburetor, you can feel the power piston. With the engine off, you can push it down and feel it spring back up. With the engine running and the screwdriver on the piston, you can open the throttle and watch the screwdriver jump up.
Wow thanks so much gents. Definitely some things I will try. This is by FAR the most professional, helpful, and friendly board I have ever been a member of, and I have been on a lot; everything from speed boats and diesel trucks to rc aircraft and saltwater aquariums (yes I love hobbies of all types!). It is amazing how one little issue can lead you down so many rabbit holes. I thought I had this thing set up fine, but I am learning that just when you think you know what you are doing, something comes along and throws you for a loop! I had no idea that the damper could be off or the throttle blades could be too open at idle, etc!
Below is a picture of the screwdriver in the vent resting on the power piston. I sincerely doubt whether that is your problem, but it's easy to check. As far as the throttle blades being open too far, the Q-jet primaries are super efficient requiring very little throttle opening to idle. If the blades are open too far, the carburetor starts to run on the mains and gas will begin to feed from the primary nozzles (nozzle drip). The symptoms are always the same, a very rich smell at idle, completely unresponsive idle mixture needles, and a hesitation at the low speed transition from idle to on the gas.
Yep... those symptoms sound familiar, except the hesitation. However, my perception might not be accurate as I've never driven another 455!
curious, have you backed out on the idle mixture screws at all or twisted em in w the vaccum gauge hooked up, to get the best idle vacum??/
Yes that is how you want to adjust the idle mixture screws. Start out by lightly seating both screws with the engine off. Open 1 1/2 turns and start the engine. Adjust till you get the highest vacuum reading. Then turn them clockwise a 1/8 turn or so. Make sure you're throttle blades are as close to closed as you can. That includes the secondaries too. You want a very small opening in the transfer slots so most of the air is coming through the idle system and those adjusting screws and not past the primary blades
You should be able to kill the engine by seating those idle mixture screws. If not too much air is coming in past the throttle blades (primary or secondary) or a vacuum leak. You can adjust idle rich/lean by the APT screw that is in the center front of the base plate. It is a tapered tip machine screw that protrudes into the cavity that the power piston tip rides in. By moving that screw in or out it raises or lowers the power piston. Unless somebody has fooled with that screw it will be behind a small tamper proof cap. But easily removed for idle fine tuning. One other thing that is commonly done and that is while using the thicker base gaskets the mounting bolts up front and nuts in the rear are over tightened. Warping the body. That's why I like the thinner gaskets that don't compress as much.
As Jim mentioned you don't want the mechanical advance moving at idle. A little stiffer spring will cure that. You can mix and match differing spring tensions to get where it is stable at the lower rpms. Different sized weights can also be used. It's all bases on centrifugal force. I make up springs too as was also mentioned. Easy to do and cheaper and less time waiting than buying them.
Ok so the plot thickens. I said the heck with it and removed the thing so I could study it off the car (sucks to be short and try to work over the fender!). I found some interesting things for sure.... 1) There appears to be a decent amount of fuel soaked into the air horn gasket and around the accelerator pump. Could that be a sign of a improperly setup float? I also recently had the car tilted pretty far up on one side while removing an inner fender for an unrelated project. I did smell fuel at the time, so perhaps this is fuel that spilled out of the float during that whole ordeal... 2) My idle adjustment screw was almost all the way out. Backing it out all the way left me with this: You can see that that throttle blades are pretty oblique to the throttle bore, and the transfer slots are pretty exposed. 3) I could not figure out why the heck the throttle would close all the way. Was there binding? Was it broken? After some tinkering, I figured out it was the fast idle adjustment screw that was the issue... Backing it out allowed the throttle blades to close more, leaving me with this picture with, both the idle and fast idle screws backed out so that they are not moving the throttle blades. So, it would seem that my idle transfer circuits were very exposed as you guys suggested. I also have that fuel logged airhorn gasket, which is a bit of an unknown. I removed the idle mixture screws and blew the holes out with compressed air. I could not see any obstructions. I have not run it yet, as I wanted everything to dry out on the bench really well. I am also a bit concerned about that gasket, and whether or not it needs to be replaced, or the float checked. I have not messed with the float, and it was set by Ken from Everyday when he built it about 2 years ago, so I trust that he did it right for sure. I always use a torque wrench set to the service manual torque to install the carb to the manifold, so I don't think I warped it, but that doesn't mean it didn't come like that. I don't remember there ever being wet gasket in the past. The other weird thing is the fast idle screw. I am pretty sure I have not touched that thing, so it has probably been like this the whole time it has been on my car. The choke is a bit of a mystery to me (electric kind), so I am not sure what I now need to check on that to ensure it is still set up properly. Time to bust out the service manual again.
It is possible that the air horn gasket has shrunk up a bit, especially since it sat for a couple years, so snug up all those screws, and the base plate screws too. As far as electric choke operation, the choke flap should just be lightly held closed when the engine is dead cold. The choke pull off should then crack open the choke about 3/16" gap immediately when the engine is fired up. Then the electric choke coil should open the choke gradually the rest of the way until the engine reaches operating temp. The electric choke coil can be adjusted to open the choke more slowly or more quickly by loosening the 3 housing screws and rotating the choke coil a small amount. The choke operates the fast idle mechanism, which is a cam plate with numerous steps on it. The fast idle screw contacts these steps. When the choke is closed, the screw should contact the highest step. As the choke opens, the cam is moved and the screw contacts lower and lower steps until it does not touch at all when choke is fully open, and then the regular idle speed screw takes over. If the throttle is not touched the cam will not move to the next lower step. That is why you have to whack the throttle to get the idle speed to drop after the engine is first started cold. Hope this helps.
If the idle mixture screws are unresponsive then air is being drawn around the idle system and not through it. Hopefully by backing out the fast idle cam screw it will close the blades so the right amount of transfer slot is exposed. I wouldn't be too concerned with a wet gasket. Dry it out and reuse it. Setting the floats is pretty at straightforward but you'll have to remove the air horn. A 5/16" setting should be real close to what you want. Most likely Ken set it in that neighborhood. You should be good there.
I have had my carb apart probably ten times in the last two years. Usually its making small adjustments here and there in hopes of finding tiny improvements. I have re-curved my distributor probably three or four times now. Here is what I have experienced so far. Mine is a (presumably) stock 430 but makes 22" of vacuum in park @ 775rpm. When I got the car it was making closer to 15-17" at the same rpm and I have not done anything internally to the engine at all only corrected vacuum leaks and tuned it. 1. Float setting is VERY important. It effects pretty much every aspect of how the dang thing functions. Having a float setting too high can cause the engine to idle funny. 2. You would be surprised at what a set of fresh gaskets (I have a carb shop literally down the street from my house lol) will do. I have found that even if the gasket looks good they really can only handle being taken on and off a few times before losing effectiveness. 3. Accelerator pump!!! get the one that Cliff sells. I had to make a minor adjustment to mine as the garter spring was not quite as taut as it should have been but now it works awesome. 4. Slight gasket matching mod. I noticed the driver side accelerator pump shot was not pumping out as much fuel as the passenger side. I opened the driver side gasket passage with a slightly larger sized drill bit. This evened the streams out and solved a off idle hiccup. regarding the distributor 1.Get a hold of the distributor spring kit from Crane cams. The Vacuum advance that comes with it is way too easily actuated by an engine that pulls decent vacuum even when the preload is set to max. A homemade limiter on a stock style canisters works a lot better. 2. Use the bushing that comes with the kit. It pumps the initial timing a little bit and limits the max. I have found that my engine runs best with about 30-32* total mechanical advance all in around 2k rpm. Current set up is light (yellow) spring and silver (medium). 3. Use manifold vacuum for the advance. My engine is smoother more responsive and runs significantly (as in 20+ degrees) cooler with a constant vacuum source at idle.
Wow this is driving me nuts. I had the engine warm, choke off, and the primary throttle blades all the way closed, and then I went to adjusting the mixture. With the blades all the way closed and the mixture screws out approx 1.5 turns, it would idle at about 500-550 with 14" hg of vacuum. I adjusted the mixture screws first before even touching the curb speed to make sure the dang throttle blades were not over exposing the transfer circuits. After adjusting the mixture screws, I saw 15" hg. I then bumped the idle up to about 750 and readjusted the mixture, but could not get higher than 15". The mixture screws were a little more responsive, but still didn't change much. I tried closing the idle mixture screws all the way and the engine did not like that. it BARELY stumbled on, but still chugged and stalled off and on like that. I guess there is still some air getting in somewhere. I checked for the base gasket leak again and it was good.I have sprayed the throttle shafts and they are good. I looked down the primaries with a flashlight and did not see any drip when idling. I still need to check the power valve with the screw driver when running to see if it is not seated... but before I did, the thing that happened in my OTHER post happened.... argh! Edit: The airhorn gasket which had tried out is now soaking wet again. Going to check the float for sure now. Perhaps it is leaking internally and dripping below the throttle blades?
