Need Help I have a 1972 Fiat 850 spider thats all orignal and with help from every one here last summer I have solved my electrical problems no more hot coils dim lights etc. Thanks every one. Over the past winter my now 17 year old son and my self pulled the engine tore it down cleaned decarboned replaced all gaskets seals new head old one was craked by exhaust manifol studs . Built nice 4 into 2 header for it and put on very nice paint job. Car starts right up runs good from 2500 rpm and up but can not get it to idle smothly. It has a 300 to 400 rpm surge . This was pretty much the case last summer also. Rebuilt carb read all the weber tec tips made some but very little improvement. Is there a direct bolt on replacement avaliable out there so I can throw this 30dica carb as far as I can. Engine is stock except for header low milage dosnt smoke use no oil has good compression and will run at higher rpms like a champ.Any sugjestions for direct bolt on no modifcations dependable better fuel milage nice smoth idle.Being a 1972 all the emisions stuf is going where it belongs in trash .Would like to keep oe air cleaner box for show reasons . Sugjestions links ???? thanks George

how are your motor mounts. does it still surge if you disconnect the throttle cable from the carb. sounds kind of odd, but may have a soft mount that allows the motor to rock, pulling on the throttle then letting it off.

Over this winter engine recived all new gaskets, seals ,timing chain and gears, head , decarboned. Had the carb problems befor this also. I DISASSEMBLED carb cleaned set float new needle and seat new gaskets. It acts like I have no idle circut at all. I did read on another post somewere that to clean the idle circuts plugs need drilled out to gain access to them. I have a very strong automotive back ground 30 years from in shop to parts counter pro.I am by no means a weber carb person at all but with a little good directions i can make it happen.Remember I stareted in this field i the 1980s when carbs were dissapering an fi was taking over.Car starts right up cold a little hard to start warm but will start. Idles very poor low as it will stay runing 1200 rpm, surges loopes 1200 to 1500.Can take the one and only mixture screw out all the way ,remove it from carb completly and it makes no differance at all.The only spot it does affectis 1/2 to 1/4 to bottom where it will shut car down.I have read the weber adjustment and tuning guide sever times ad carb is not responding as it should.I worke in the small engine industry for a few years and recall welsh plugs in some carbs had to be removed to gain access to tiny screens that would trap dirt and become pluged. I have blow up of carb and dont see any such refferance . What if any thing needs drilled out to achive complete cleaning. Picks advice anyone. I know the 850 spider seems to a be the black sheep of the fiat family every where I go any help appriciated. George

You might switch out the throttle cable. It's a wire rather than an actual cable, and as such it binds in the housing on the way back to the motor. Mine got replaced with a brake cable from a tandem bicycle because of the same symptoms, and it transformed the car. It's cheap and easy.

mayby your jets are too big

Jets are the right size, only likely plugged.. Idle fuel jets on these things plug and are sometimes stubborn about staying clean. You do not need to drill/etc.
Does idle improve with hand over carb?? or choke slightly closed? If so, yes, idle mix system defunked ( that's a tech term)
Can you post of blow-up of that carb?

Tore down cab today soaked every thing in deep creep reassembled adjusted and works perfect. Next problem #3 Cylinder is getting antfreze in it when car is shut off.Has new head 1.7mm gasket from C J Oberts. Going to try retorquing. Any insite?? Retorque hot cold warm ???

glad to hear you got it under control
cold
try some barrs stop leak

Tore top end back down Sunday 3 bolts near # 3 were so lose you could turn with your fingers. Retorqued to 40 ft lbs.Is it common for them to come lose I didnt use locktight but did give them all a good coat of permatex thread sealant . Went for 1 hr ride shut off car came back latter Still got very small leak in #3. Against every thing I belive in seals leak replace it gasket leaks replace it etc. Because of lack of good machine shop near me and part being so hard to get for this car in went the dreaded bars leak. Three days later no more leaks I know this is by far not the correct thing to do but whats a man to do. My 17 year old is looking for a elcamino to build his Fiat days are coming to an end.