tuning idf carbs-Questions

[bman]

Hello, I have couple questions on tuning these things. My setup is as follows 2liter engine -40/80cams,9.8 pistons,large valves and springs, 70 idfs with 52 idle jets,mains 130,air 200, vent 32 . I have a sychrometer for balancing the carbs.I know the initial setup for tuning is to set idle mix 1turn out and speed setting 1/4 to 1/2 out .Air bypass screws all the way in. The engine idles great with with all 4 idle mix screws turned all the way in,and speed screw barly touching(idling between 850 and 1000 rpm),which led me to believe that idle jets of 52 are to large.The spark plug might show it running a little rich but not to bad.On the scale of the sychrometer the front carb of each cylinder is 5 on the scale and rear carb on both is 7.Backing out the idle mix screws does very little to changing the sychrometer,of course the engine speeds up or slows down-actually runs worse with idle screws not turned all the way in.Ive tried 50 and 47 jets as well,it runs well with idle screws all the way in also??? Any ideas? Do I need to get smaller jets? Or am I doing something wrong or missing something? As to sychronizing the carbs,what am i looking for,the highest equal volume on all 4 cylinders,do they have to be exactly the same? My concern is to get the car to pass emissions eventually.

[So Cal Mark]

you need to sync the carbs and idle speed is critical. If the throttle opening isn't perfect, the plate won't be in the proper postion with the progression holes, causing stumble on acceleration. Your jetting sounds like it's in the ballpark.
If you can't get the throttle plates in the right position, you might have to drill holes in the throttle plate. Set the idle speed with the two carbs disconnected from each other initially

[mdrburchette]

Like Mark says, make sure the throttle plates are closing. You initially want to start with the linkage disconnected to ensure this. You've got the air bypass screws all the way seated and you're showing 5 on the front choke of each carb and 7 on the rear. By opening the bypass screws, the vacuum will increase, so the higher number is what you want as your base to synch the rest to. So, open the bypass screws until you get 7 across the board. Once you get your vacuum the same in each choke, you can start fine tuning.

[So Cal Mark]

good advice Denise, but I'll again stress the importance of setting the speed settings with the carbs disconnected from each other before adjusting the air screws

[mdrburchette]

Yep, that's what I meant.

[gary124sport]

Here's what Denise and Mark are saying. Sync the air flow / vacuum between the barrels of each individual carburetor BEFORE you sync the two carburetors to each other. Turn all the air flow screws in. Then working with one carburetor at a time turn out the screw of the lower flow barrel to match the higher flow barrel. Do the same for the other carburetor. It is best to do this with the engine running as slow as possible thus increasing the sensitivity of the measurement. Also, as Mark said make sure the throttle plates are closed otherwise the air correction screws effect is negated. AFTER this is complete then balance the carburetors to each other with the linkage screw between them. I've bee running twin IDF's on mine since 1982 and they are very easy to maintain once they are set up and you understand how they work. They require very little attention once dialed in.

[bman]

Everyone thanks for your replies,ill check what you suggested.There dosnt seem to be problem balancing each cylinder on either front or back carbs. Now the linkage adjusting screw where is that? Are there two separate shafts with some type of collar that mates both of them together? If so should that be loose when working on each carb individually ? Should I start out with the smallest idle jet since it didnt seem to make a difference?

[So Cal Mark]

there are levers with an adjustment to synch the carbs together

[FMO]

Here are a couple of links how to tunes a pair of Weber IDF\ s

http://www.rescue912.com/spider/WeberIDF_Tuning/
http://www.redlineweber.com/html/Tech/i ... ntrols.htm

regards
FMO