I have just had my original 400 rebuilt. Everything was pretty much stock, .040 overbore, except for the cam. I installed a TA 212 cam. The car is an automatic. I am having trouble adjusting the carburetor. Initially I set the timing to 8 degrees and the carb screws didn't have much effect on the way it idles. I have about 6-8 lbs. of vacuum measured on the advance line. I increased the timing to about 15 degrees and now have about 9-10 lbs. of vacuum with minimal effect on the carb adjustment but the idle is better (I had to re-adjust) and it doesn't cut off when put in gear. I have checked for vacuum leaks everywhere and can not find one, even replaced all hoses except for the brake booster. Are there any recommendations on where I should set the initial timing? Do I need to have the distributor degreed? What other things should I look for?
Your vacuum is way too low for that size of cam, you should be reading an easy 15-18" of manifold vacuum ( the advance hose is ported vacuum and you should have almost zero at idle) at 8-10 btdc timing and 725rpm idle. Start looking for leaks. Be sure you don't have a bad plug wire or other failing ignition component. Good Luck.
Checked the wires, they all seem to be good. Pulled each of them one at a time. There are only 4 vacuum ports on the intake. One for the brakes, one for the PCV valve, one to the transmission, and one for the heater controls. Sprayed carb. cleaner around all 4 with no change in the way the engine runs. Sprayed carb. cleaner around the base of the Carburetor and around where the manifold meets the heads and still no change. Any other suggestions? Is it possible that the manifold is bad? It is the one that came off of it and it was running fine before the rebuild. I have the manifold torqued to 45 lbs. Should I retorque it higher?
does it smell like the car is running rich. maybe the fuel bowl is leaking into the manifold, which would cause the idle mixture screws to have no effect on idle.
Was the cam degreed? Correctly? Definitely make sure your vacuum advance is using a ported vacuum. I just made the mistake of using full vacuum on my vac advance and it made my car miss really bad....a very erratic miss...sounded liek I had a big cam. Check that... I don't know what to say about degreeing cams, but it seems to have been a problem with other folks before.
First check to make sure the carb is only getting fuel from the idle circuit. Run the mixture screws in all the way to make sure the engine dies. if not, you are getting fuel from elsewhere in the carb. Torque spec sounds right. As mentioned you should have more vacumn that that. A very poor mixture will cause low vacumn.
You didn't say if the heads were milled and/or the block itself decked. If you did a lot of either or much of any combination of the two, did you check the fit of the intake manifold relative to the mating surface of the heads? If there is a mismatch here, you might not see any change when you spray the top side of the manifold since that side may fit much more tightly than the bottom. If you go through the carb tricks listed above and still can't find anything, try putting your hand over the choke horn to limit the amount of air getting to the engine, or manually close the choke until there is a difference in how fast the engine idles. If it drops RPM, there is no vacuum leak, if it picks up in RPM, there is a vacuum leak and you just have to find it. Keep in mind that anything connected to any part of the vacuum hoses is a potential leak. It's almost never something odd like the brake booster diaphragm or the Vacuum modulator on the trans. It's usually something way too obvious like the line at the modulator end is disconnected or old, cracked and brittle. Start with the easy and obvious stuff first. There is a reason it's the obvious and easy stuff.
Thanks for all the help! The carburetor is not running on the idle circuit. The idle is turned up too far and the throttle plate is slightly open. Did not have a chance to work on it last night other than to check that out. I will probably have to bump the timing up some more to be able to lower the idle screw enough. There seems to be plenty more room for increasing the advance. That will be my first attempt tonight. More to come. :grin:
I have bumped the timing up to aroud 15 degrees initial timing and about 36 degrees total timing. The carb is now on the idle circuit. The adjustment screws are about a 1/4 turn from bottoming out. Do I need to have my carb modified or are there other areas that I should be looking at?
A few questions for you.. .....1) What's the RPM? .....2) Have you checked the dwell? What is it? If you change timing or dwell, the other will change and need to be reset also. .....3) Is the vacuum advance disconnected and plugged while setting timing? .....4) Where are you measuring vacuum from, manifold or ported? .....5) Is your distributor hooked to ported vacuum or manifold? .....6) Float level? .....7) Have you tried this trick? If you have already tried these things, I apologize for restating them. Assuming that everything is mechanically sound, tuning is a balancing act like walking a tight rope. Idle air/fuel mixture, timing, dwell, idle speed, they are all intertwined. Hope I've helped
I am assuming you using a O-jet. That seems to be way too lean. What are your new vacumn readings? I realize it is just an idle only situation (for the most part anyway) but it will cause the engine to run a little hot if lest idleing for an extended period. If it is a quad what are the numbers on it? Adjust the mixture screws. for max vac or idle and then slow down with the idle screw
im still guessing theres fuel leaking into the manifold through a plug in the carb. but 15 initial and 36 total seems about right, thats what im running with my dist converted by dave. i assume the timing, dwell are correct and that your tuning for the highest vacuum or at least highest idle.
I am not sure what the engine RPMs are, I don't have a tachometer. It is too low, will try bumping it up a little. I have a Pertronix ignition, no dwell reading. I am measuring manifold vacuum from the advance port, I understand that on a 1967 it is unported. I will hook it to the transmission vacuum modulator tonight to confirm that it is the same. When I covered the air horn, the engine died so I don't think that I have a vacuum leak. The block was not decked during the rebuild. The heads had a very small amount taken off just to clean them up. I am tuning off of the idle circuit as far as I can tell. the throttle plate is completely closed at idle now. The quadrajet carb number is 7027146. I am planning to try it again tonight after work. More to come.
First of all, go down to Sears (or somewhere) and buy yourself a tach/dwell meter. The cheapest analog version, they work better than digital IMO. Should be around $10-20o No: Adjust the mixture screws. for max vac or idle and then slow down with the idle screw. You have to have all three; tach/dwell meter, vacuum gage and timing light to do the best tune. It definetely does not hurt to make only one change at a time and write this down in a notebook, along with an evaluation of that change. This advice works from novice all the way to the most experienced mechanic. Trust me! Back to your problem(s). Is it still running rich at an idle? Why do you think this? Smell? What is your true intake manifold vacuum right off the manifold? (lowest fitting on carb, or the fitting on the manifold that goes to the tranny) Have you checked the float level? If you look down the primary venturies, do you see fuel dripping? Hope I'm making sense and helping..
The manifold vacuum is 8 lbs. measured at the transmission port. When I crank it up cold it will not idle until it warms up a bit. Plenty of black smoke probably unburnt gas. Once it idles I no longer see the black smoke nor does it smell strongly like gasoline. It just doesn't idle properly and the mixture screws have little or no effect. Looked down the carb. and did not see gas dripping. Couldn't stay up there very long though. Tomorrow, I plan to double check that the cam was properly degreed at 4. I am grasping at straws now but I want to make sure. I have not checked the float level but have put my backup carburetor on and it acts the same. I am sure that the problem will turn out to be something very simple that I am overlooking but I just haven't found it yet. I will stop by Sears tomorrow and purchase a cheep tach.
It sounds like what everyone is saying should o No: make some differences in your vacuum reading. I'm pretty sure that you shouldn't even try to make any adjustments until you get the engine warmed up to at least 160. If you do any adjustments cold, they will not be the same as if the engine were warm. Also, one thing I learned when tuning my car is that you will find a very small range of tuning that will get good numbers, such as 17lb vacuum, plugs look good, doesn't huff at idle, responds to hard accel. and idles around 850 rpm. When you adjust your carb do it in small increments until you start to see improvement, if you go too fast you might over shoot the sweet range.
