http://www.ferrarichat.com/forum/showthread.php?t=20179&highlight=308+Carb+Sync I followed Birdman's carb sync tutorial yesterday in an attempt to sync my carbs. They were fine before I moved down to texas and the elevation change caused them to run a little lean and the idle was a bit low as well. In my ignorant attempt to adjust the idle (turned the wrong screws!!) and richen up the mixture (got that part right) I screwed up the sync of the carbs. I bought a SK Flowmeter tool and set to work following Birdman's thread. However, I could not get the front and back to even get close to the same by just using the linkage arms. The only way I could get the front to slow down was to use the linkage (which also caused the rear to slow down WAY too much - almost stall) and then to use the idle adjustment screw on the rear carbs themselves to get the 4kg/hr. I did get them all to match up (didn't get to test drive it yet but I will today. So my question is, did I do it wrong? Should I only be using the opposable thread linkage to adjust the airflow of the carbs? I fiddled with it for quite a while and just could not get the front/rear the same without using the idle screw. Note that it did not take much and I only used it on the one bank. THe other bank I set it so it just touches the side-to-side linkage and essentially does nothing. Thanks PS Yes, I searched the archives. Saw a lot about carbs, but didn't see to answer my question.
It takes a bit of fiddling with the linkage rods, and idle stop screws, but I can get my carbs spot on. Back off on the throttle cable adjustment nut also, there should be slack in this cable and it should not be used to set idle. The idle mixture screws should only be messed with in the very end. I usually set them at 3 turns out to synchronize. Maybe you have another problem, ie: timing, float level or spark on each bank. Once I get the carbs synchronized , I go back and try to get my idle down as far as I can go, then mess with idle mixture screws to get desired idle mixture (turn screw in until idle backs down, then turn ¼ turn out), then check sync again at idle. I rarely use idle stop screws to set idle because this causes backfiring when coasting (foot off the throttle), as the throttle plate is in the wrong orientation in relation to the progression holes in the throat of the carb. Also, make sure you check sync at 3000 rpm as this is crucial. Hope this helps, you may call me if you want more help. John 303 697 1763
to check operation at 3000 rpm, i then use the throttle cable adjustment nut (turn it out to get 3000 rpm as read in tach).
The first I would suggest is to check the linkage for wear, as these aren't new cars. I use an aftermarket ball swivel and some valve lapping compound to "round them", as shown in the pic. The stock linkage, if worn can make it very difficult to adjust with accuracy. The next thing I would note is to take care in how you adjust the idle. A common mistake is to crank on the screw on the side that sets the throttle plate position, which is the way US carbs are done. Not with the 40 DCNF. If the throttle plates are opened too much, they allow fuel to be drawn from the intermediate circut, as the ports that feed from that circut are just above the throttle plates. If you look closely, they are usually 4 holes in a diamond pattern, just above the TP. Adjust the TP with the screws, to a point that they just close, but do not stick,and this is a good starting point. Then adjust the idle speed screws to obtain equal flow all the way around. Personally. I prefer to have the linkage disconnected when adjusting the flow, then check it afterward with the linkage on, which will tell you if the linkage is correct. If you are not able to get the right amount of flow by adjusting the Idle air screw, as often happens with big cams, and even stock cams set on different opening and closing events as a means of moving the power band upward, you can carefully drill a 040" to .060" hole in each Throttle Plate, adjacent the idle air ports in the base as this will give it a bit more air. It is best to start small, then check it. If the holes are too large, solder them shut, and try again. And it is a good idea to check for two things: base plate flatness, as this will cause air leaks, and make sure the bearings are greased in the throttle shaft, as this will eliminate an air leak there as well. HTH. Enjoy! Image Unavailable, Please Login
Well I got it figured out. I had the linkage's (top and bottom) so screwed up that when I turned one, it pushed the lever arm AND the opposite turnbuckle linkage so that when one bank would speed up it would also speed up the other bank. Basically the pivot arm b/w the two linkages was moving when it should not. Also, the low temp. idle thingy ( ??? ) was not even touching the pivot arm, even when screwed in all the way!!! How screwed up is that. I finally got the linkage's set so that one would control one bank (speed up or slow down CFM) and the other linkage would control the other bank. I got them all close, then used the air bleed screws to make each carb match itself, got the idle mixture screws set close as I could and I set the idle speed screws so that they were just touching and not really doing anything (per birdman's instructions). Also, I had to much slack in my throttle cable that I had to turn several turns out just to get it too do anything. It's all working OK now. Took it for a test drive after I was done and it pulled like it did before I messed it up all the way to redline...nothing like a 8-carb V-8 screaming at 7700RMP. Thanks for the tips. I knew after I re-read my message earlier SOMETHING was screwed up so I went back and reset everything while it was all cold so that things made more sense linkage, turning screws wise, etc... and re-started from there. Supprisingly enough once I got things back to where it made sense, it was pretty close on first start up.
Sean, Glad you got it figured out and my tutorial helped! I haven't been on line in a few days. Birdman
Kermit hit on a great point. on my old 308 i had to replace all the ball and socket joints for the turnbucklesas they were severely worn and had way too much slack in them. one of them was so worn that the arm would pop out of the socket and the linkage would jam at almost wide open throttle. imagine that happening while driving in a neighborhood or school zone. yikes! with all the new parts and the floats re set the carb sync went much better.
What kind of ball ends do you guys have? Mine have a threaded cap that screws in against the ball, and has multiple holes in the end, with several crosses in the screw cap to put a safety wire through to keep the cap snug. It has also been my understanding, that in adjusting the syncronization of the carbs, you disconnect the linkage to both pairs of carbs, and balance the two pairs with the idle speed set screws on the left carbs, and the intermediate balance between the two carbs side to side. And that when the carbs are truely synced, you put the ball linkage back on and adjust it only to take up slack, not to increase any idle speed. Am I wrong here? Paul Colberg~
I agree with Kermit and cavallo_nero. Most people immediately go to the throttle position screw which just messes things up. Here is what has worked for me for years. Needless to say, before adjusting the carbs the ignition system must be spot on, the float heights correct and no vacuum leaks. From there I usually disconnect the carb linkage between the cylinder banks and inspect it for worn parts. Make sure that the adjustment threads and locknuts work smoothly. Slop between the ball stud and the rod end can be removed by gently tightening the set screw within the rod end. If the linkage doesn't transfer positive "no slop" movement, you will never get all the carbs working in perfect unison. Next I set the throttle position screws to just barely open the throttle, I mean that it is just perceptible that the screw, as opposed to throttle plate/carb throat contact, is taking most of the return spring load. This takes some time with constantly running the screws back and forth and feeling with you fingers for the slightest movement of the throttle shaft. Once that I am satisfied that all 4 carbs are set this way I'll start the engine. Usually to keep an idle I have to manually operate the carbs on one bank while adjusting the other bank. I check the balance "throat to throat" within a carb and open the air bypass valve (from a closed position) as necessary on any slacker throat. When both carbs are balanced "throat to throat" (not "carb to carb") I repeat the procedure on the other bank. By now the engine usually is running smoothly but slow. It is at the point that I consider a good foundation to start the idle mixture and synchronization process. Many people try to target a particular kg/hr airflow which I think is a mistake. There are just too many variables not to mention the fact that a Syncrometer isn't exactly a scientifically calibrated instrument. The objective is to have all 8 throats flowing at the same rate relative to each other. If you start with the throttle plates all equal and the throat to throat flows even within each carb, the syncronization process carb to carb on each bank and then bank to bank will take only small adjustments. Granted you will be moving the flow meter from throat to throat, carb to carb for a while to get everything even but you shouldn't need any gross adjustments. After I get all 8 throats flowing at the same level I set a reasonable idle speed with the throttle position (idle speed) screws turning them both equally. If it takes more than 1/4 turn I get worried. Recheck for equal flow on all 8 throats. Remember all this so far has been done with the bank to bank linkage disconnected. Next I shut off the engine and start on the linkage. This is were one can easily destroy all the good work already accomplished. At this point the throttle shafts on the front and rear banks are resting on their respective throttle position (idle speed) screws. The linkage needs to be adjusted so that both shafts begin to move at EXACTLY the same time. Each link from the bellcrank operates like a miniature turnbuckle altering it's length to accommodate the relative distance between the stud balls on the throttle shaft and the bellcrank. If a link is too short it will pull the throttle shaft off of the idle speed screw, too long will rotate the bellcrank and pull the opposite bank throttle open. Ditto for the link on the other side. Lots of variables at work here. BTW, the high speed idle screw should be backed well away from the eccentric cam, the bellcrank rotated firmly to it's closed throttle position and there should be some slack in the throttle cable. Typically I will adjust the links a little long to insure that the bellcrank does not reach it's stop before the shafts come to rest on the idle speed screws and to allow some "cushion" for the inevitable idle speed screw adjustment to come. When I think that I am getting close to what I need I'll secure the locknut on one end of each link and continue the process by just slightly rotating the other rod end. It takes quite a while to get the linkages adjusted correctly and this is one case where "close enough" isn't good enough. I have found that even small differences in the torque applied to the last lock nut on the linkage can be the difference between crisp throttle response and a slight hesitation. If your hand is large enough, you can put your thumb on the throttle shaft arm where the idle speed screw hits (rear bank) and stretch a finger to the same place on the front bank. Use the other hand to pull on the throttle cable (don't push or pull on the linkage itself) and you will be able to feel even slight differences in when the throttle shafts start to move. Sometimes you might have to put a finger from each hand on the shafts and have a helper operate the cable. Once you have reached carb synchronization Nirvana, use the high speed idle cam (and maybe a small stick) to hold the engine speed at 2-3000 rpm and recheck the flow rate on all 8 throats. If one bank is now different than the other, your linkage is not yet adjusted correctly. The throttle response should now be nice and crisp. Also have a helper hold the gas pedal to the floor and confirm that the carbs are fully open (engine off of course). Adjust the cable to achieve full open throttle and a bit of slack at idle. Dont get hung up on a certain number of turns of screws or kg/hr. Too many variables for anything other than ball park figures. Luigi at Rockos Auto Palace may have ran your idle mixture screw into its seat with 50 ft. lbs. of torque back in 1983. Now instead of a nice taper it looks like an hourglass and flows more fuel at 1/2 turn out than your buddies idle mixture screw does at 4 turns out. Getting those two little links adjusted just right, although often downplayed, is IMPORTANT, IMPORTANT, IMPORTANT. BTW, those adjustable links, rod ends and ball studs are American sized. Although most new ones are now plastic, the old metal style can sometimes be found at vintage tractor and car supply sources. I hope that I havent added too much to the confusion. There are probably things that I do intuitively and have failed to mention. This is sort of a "start from scratch" procedure as I have found that trying to build on what settings are already there usually results in chasing your tail around the tree. To recap, the goal is equal air flow in all 8 throats (relative to each other) at any RPM. All throttle shafts moving at exactly the same time. Minimal throttle plate opening at idle to avoid engaging the progression circuit. Proper mixture as set with the idle mixture screws.
I have the same ball-ends as you have Paul and yes, you adjust those screw parts till they touch the ball, but not overly tight that they drag, but not too loose either that they slop. I always safety-wire them afterwards. I adjust those ends and leave them on there and just remove the rods to do my sync'ing. When set, I thread the rods back into the ends and set so that they keep the carb adjustments without affecting them (Like Sean mentions how he discovered how turning one more cranks the other bank of carbs more open). Kermit, I have tried your method many times before using the air-bypass screws to set idle speed and have never had success. I've always used the throttle-stop screws and with that, have achieved proper idle speed and smooth transition through those progression holes. Is it just a fluke, or are my (stock and what appears to be all complete and original) carbs that well dialed in from the factory? My progression holes look like these in the photo below (pictured from the bottom of the carb, so is an upside down view): Image Unavailable, Please Login
This is where I had a problem. When I moved the turnbuckle, things just did not move right. It just did not make sense and once I posted and read it to myself, I said "Something's wrong"!!! So I went back out to the car (it was now cold from overnight shut off) and started playing with the turnbuckle/linkages and realized they were not right. I messed with them until the moved in a way that made sense (like you said, at the EXACT same time) and started over from there. It runs nice now although I'm not sure that the kg/hr is exactly the same through the rev range as I did not test it. But when I held it at 1500 they were all pretty close.
same ones. the problem with the turnbuckles and ball joints on my old car was the threaded screw ends were so worn out and the balls were so worn down that they had slack in them , even with a cotter pin or safety wire in place.
Dealer or FoUK has new ball ends of an updated design. The original metal is soft and they'll wear to an elongated oval which introduces "slop" in the mech and hence means your sync'ing efforts are not rewarded as well as they should be once off idle. Philip
Peter, you are one lucky SOB, LOL! Yes, those are the idle transition into the intermediate circut. And haveing it turn out right is quite unusual. As you can see, they aren't toofar off of fully closed, hence the advisement to watch for this. Miked hit it all pretty muchright on, especially the throttle end travel. I once failed to check that, and after an exuberant dyno run, found I had bent the pedal mechanism. OPPS! I used a standard ball end, available at places like McMaster Carr, took the nice hardened ROUND ball for the lapping. The stock ball being attached to the carb linkage prevents doing much with it, and this method tightened them up clearance wise. Philip hit it right on the head. Even the perfect synch job, if the linkage starts pulling one carb open before the rest, due to slop, it will be into the intermediate circut (fat running there) and the rest wont be opening yet. So to get the right RPM idle, one carb/cylinder is dialing in while the others remain on idle circut only,and dialing out that miss can drive ya crazy!
