No connection to your problem IMO. I ran my ex-'78 308 at both 3 deg ATDC idle (when it had the stock R1/R2 set-up) and at 7 deg BTDC idle when I went to a single-trigger (Crane) set-up. The only difference was that at 7 deg BTDC idle, the airflow thru each barrel had to be reduced to ~3.5 Kg/hr to hold the 1000 RPM speed; whereas, at the 3 deg ATDC timing, the airflow was more like ~4 Kg/hr at 1000 RPM (so this make things less sensitive to slight mechanical wear/variation in the throttle plate mechanisms) -- but, in each case, no problem returning promptly to 1000 RPM after releasing the throttle (and 3 deg BTDC would just be ~1/2 way in-between those two values). I checked my old notes and the "average" amount the idle screws were open was more like ~5 turns (rather than 4), but as Philip suggested, you can just try optimizing the mixture on each cylinder when you're running at the 1000 RPM speed. If all cylinder are working you should only have an RPM drop by going too lean or too rich. If the idle RPM increases then you go back and reduce the airflow to reduce the RPM (and retweak the mixture again at the new airflow). Bottom line is that when you think you've got the mixtures right, and it's running at 1000 RPM idle, as you pull each spark plug wire you should notice an RPM drop (and "hear" the intentional miss).
Docweed, my .02 The idle 'mixture' screw only adjusts the mixture coming out of the lowest progression hole which is the one which should be operating when the engine is ticking over. If this idle mixture is not correct, the only way the engine will run is with the speed screws opened some more so it runs on the other progression holes but then only at around 2000 rpm. So I think if you get the idle adjustment correct on all carbs then it will idle at 900-1000 rpm. There are various ways of doing this - colortunes, CO meters, looking at the plug colour, exhaust smell. In my (limited) experience they all work reasonably well. You guys with more experience, please shoot me down in flames but I'll stick my neck out again . When the mixture is more or less correct, the most sensitive way of fine tuning the carbs I found was to put your fingers over the throats and therefore introduce a restriction. If the engine speeds up it is too weak, slows down it is too rich and so on. Hope this helps...
34 degrees BTDC should be the advance on the crank at 5000 rpm (engine speed). 7 degrees advance at idle is fine. Overrun is after you have accelerated the engine to higher RPM and then release the throttle. RPMs come down. I understand it is hanging at 2000 RPM. I'll repeat my point, I think your idle mixtures are too rich. The engine is happier at higher RPM as the mixture is being diluted with a stronger airflow. Back the mixture screws in as advised and see if that cures your problem. If so, you are done and not faced with pulling the distribs. Philip
Thanks everyone for your advise...I'll try them tomorrow if I can. Two things I'd like to mention as they may be significant. 1. there is a strong smell of fuel so that should suggest the mixture is too rich and 2. the air flow measured with my synchometer (even though it's a relative measurement) is about 8 Kg/Hr at 1000 rpms and most data that is mentioned in the threads say around 4 Kg/hr is more common. Would this suggest anything and if so what should be done to deal with it? I should say that when I started to do this tune up all throats were the same and this was the measured amount. In any event I'm anxious to try your suggestions. Tip: You guys probably already know this but maybe it will help someone that hasn't heard it. I mechanic mentioned it to me today. If you suspect a vacuum leak just spray some carb cleaner or ether on the possible leak and if the engine increases in rpms then you have found a leak. Don't get any sprayed in the intake or you will also get an increase.
Something is definitely screwed up. 8kg/hr would make the engine lean, but you say there is a strong smell of fuel, but you will smell the fuel on top of th engine as you lean in to turn screws etc. since everything is opened up. Are you sure you don't have the idle speed screws turned in? The two idle speed screws should not be touching the stops on the carbs while you are setting the carbs (or they should be 'just' barely touching). It sounds like you turned the turnbuckle to far and the idle speed screws are holding things open causing high air flow. Also, check that your warm-up regulator is not hanging up things. It's that device off the water line in the valley of the V with a rotating arm on it. There is a screw that will push on the throttle linkage assembly b/w the carbs and hold the idle RPM's up when the engine is cold.
Sean Thank for yours comments because it brings up a point that I don't understand. Yes the idle speed screws are turned in slightly (the ones on the driver side carbs. and see my comments about the adj screws on the center linkage below). I started by setting the idle screws just resting on the stops with no movement of the throttle levers. The other adj screws were as follows: air bypass to the seats and the mixture screws out 4 turns from seat. I disconnected the linkage from the pivot lever between the four carbs. I'm working by myself and I could not get the car started. It would not run long enough for me to get back to manually work the throttle levers so I turned the idle screws in maybe a half to one full turn just so I could get it started. I then turned the screws to obtain 1000 rpms. I did this so I could proceed with the synchronizing. I then turned one of the screws to balance front and rear. (All carbs. are balanced it this point.) I thought I'd do this first then deal with the idle. I know the idle screws should not be open much as it affects this progression circuit deal. Here's my question if the linkages are removed and the idle screws are not supposed to move the throttle plates how are you to obtain an idle? Do you use the air bypass screws or mixture screws? All my air bypass screws are all the way to their seat except one. Another question what are you supposed to do with the adjustment screws on the center linkage? I started by turning the screws out so there was no contact but the backup spring keeps it in contact. I did adj them to obtain side to side balance but I have no idea where the starting point s/b. Could there be something wrong in that center linkage adjustment on both front and rear? If I remember correctly those screws were turned in a lot. Is this part of the problem? I'm curious about your thoughts on this center linkage as I read in a past thread that you were supposed to leave this adjust alone and only change it get side to side balance. Some other threads in this post suggest I spend more time adjusting the throttle mixture as I may be too rich. I admit that I didn't allow enought time for the carb to normalize and I smell fuel out of the exhaust. Oh there is no interference on the warm-up regulator. Well thanks again Sean for any suggestions. .
OK, undo all that. Do not allow the idle speed screws to set the speed. Its hard to explain w/o a photo so bear with me. On the drivers side carbs, on the right side of those carbs (as you look from the back) is a screw that faces you on the front and rear carb. Do not allow that to touch the stops. Unscrew it all the way. Hook back up the turnbuckle assembly and get both lengths about equal. If the car will not start, use the thottle cable to pull on the assembly and act like you in the car pushing the peddle. Loosen the nut where it passes thru the front cam cover, screw out the assemble a little bit and then tighten the nut. Dont worry, well undo this later. You cant, (see above). The turnbuckle assemblies will mess this up when you re-hook them which is why you dont use those two idle screws to set the idle speed. And that is all they are used for (side to side balance) not for setting idle speeds. They will always contact the assembly. Dont try to use them to set the idle speed or youll get yourself in a bind. I did the same thing. You need to go back to step ZERO and start over (sorry to say). Get those turnbuckles hooked back up and get them about an equal lenth. Back the idle screws out so they dont touch anything (the ones on the front an rear drivers side carbs). Put the air bypass screws all back in all the way closed. Use the throttle cable to artificially speed up the car and start. Try to get it to 1500 RPM or so using the throttle cable. Now, using that screw that is on the linkage b/w the rear carbs, adjust that in/out until all four throats on the rear are about equal (this is the side to side balance screw). Now do the same to the front bank (this screw is hard to reach b/c it faces the front of the car). Again, get the 4 front throats about equal (the front and rear will likely not match each other but should be close to 7 kg/hr dont worry, well fix this in a minute). Now play with the turnbuckle assembly to get the front an rear equal. Make small adjustments b/c just a little turn will make a big difference. Now go to this excellent post by Johnathan and start at post #11. http://ferrarichat.com/forum/showthread.php?p=67313280#post67313280 If you get totally confused, send me a PM and we can hook up on the phone and discuss it.
Sean You don't know how much I appreciate your help...thank you. I'm going to do exactly as you instruct but I am going to have to pause for a short time as I think I need to rebuild my carbs. Let me explain. This morning I when to the garage to try some of the suggestion you, Steve and Phil gave me. I figured I'd start from the begining so I started by checking for vacuum leaks. I was removing the idle jets and I found a torn O-ring. I went to the local foreign car parts and got 8 new O-rings. We thought the same size (1/6 thick, ID 3/16, OD 5/16). Replaced all of them then proceded to start over. Turned the idle mixture in to the seat and back out 3 turns. Warm up the car adj the idle to 900 rpms with the idle screws (I now know that's wrong ) and started to turn the mixture screws in 1/2 turn at a time while watching to electronic tach. As I turned it in the speed kept getting higher until the screw closed on the seat. Now I'm really confused and depressed. I sprayed some carb cleaned on the idle jet and the rpms increased. Is it leaking around the new O-rings and if so why is there such a high reading on the synchrometer (8-9 Kg/hr) and wouldn't this make it extremely lean mixture? I'm baffled and I'm sorry I got you involved in this mess. I don't want to replace the old O-rings so I'll hunt down some rebuild kits and redo the carbs. When I'm done I'll follow your instructions. I'll be signing off for a while and I hope it's OK to contact you later. Thanks. Chuck
