Weber questions

Like "seagull "wrote, I have exactly the same problem . . .misfiring and popping. This occurs primarily at idle and off the line acceleration. However, if I'm at about 3000 rpm going from 3-4th or 4-5th, its nice smooth acceleration. Also nice and smooth if I'm crusing on the freeway at 60 -70 and I punch it. But again, really lousy performance at off-the-line acceleration. What is the deal ? The mechanic replaced emulsion tubes and some jets and it runs a little better but still exhibits this behavior. I cannot figure out what is going on. I'm almost to the point of completely replacing the carbs but it seems a little costly at this point ?

-Would a rebuilt or new carbs do the trick?
-Could there be dirt in the carb bowls?
-Dirt coming from the gas tank?
-Any experience with replacing jets?
-Any experience with replacing emulsion tubes (what exactly do they do?)

Any experience wit hthese problems would be greatly appreciated. Thanks !

You didn't say your year/engine size, but I'll relate my experience so far - I have a 74 911 with 2.7 that was converted from fuel inj to 40IDA Webers by a previous owner. My research shows that these carbs are engineered for a 2.0 liter engine and need some changes to make them more suitable for the much larger engine. Call PMO @ 310-393-5423 and speak with Richard - He can't be your mechanic over the phone but he can tell you the most appropriate venturi, main and idle jet sizes to use -My venturis were 30 and recommended is 32, my mains and idles were also too small. He also recommended a slightly hotter NGK spark plug. The parts haven't arrived yet, so I don't know how completely they will get rid of my problem (popping, poor/rough normal running) but I expect to see an improvement. Unfortunately, symptoms like these can have multiple problems - I replaced my plug wires, points, rotor & distr cap to insure they were contributing to the problem. PMO also has a couple of special tools to help adjust the carbs. The prices were very reasonable, I thought - $72 for 6 venturis and jets @ $18/set. I get pretty deep into he technical stuff and I'll be glad to talk you through any thing you'd like to know more about - most of my experience is for cars before fuel injection and all the electronic control gizmos - I can be emailed directly if you/anyone would like - lturner@erols.com

Thanks for the reply. I have a '71 911 T with a 2.2. It was originally sold with Zenith carbs from the factory. It was obviously converted to Webers at some point. I had a mechanic replace some jets already and I think they replaced some emulsion tubes also. It runs better but still far from what it should be (in my opinion). I put the stock air cleaner back on instead of the K&Ks because I thought it would reduce the chance of dirt getting into the carbs. The bowls were checked and they are clean. The gas tank is clean . . thus I don't think it's a dirt issue. It was just professionally tuned with new points, plugs, timing, valve adjustment, etc. Would timing contribute to the problem ? I'll try plug wires next. I noticed some gas around the gaskets on the left bank of carbs. I am thinking seriously about rebuilding the Webers myself. It seems like a complicated task but I think I'm willing to give it a shot. Is there a book I can get to show me a schematic and details on rebuilding these Webers ? I also need to get the tools necessary to "synch" and adjust them once I re-install them. I assume I can get these from PMO. Any more advice is greatly appreciated . .. dsanguinet@earthlink.net

Poping back thru the carbs at idle is usually the result of being too lean on the idle circut.
BTW the idle circut is what the engine runs on up to 2500/3000 RPM.This can be caused by a number of things.
In my own case(2.4L),I have it down to two cylinders when the engine is cold. When warm,it pops infrequently(never at over 3000 RPM). I'm working on those.
The first thing to do is put in some fresh plugs (NGK BP5ES). This alone made a tremendous difference(the Bosch were also new).
Pull out the idle jets and check to make sure the passage is clear. If not,blow out with air.
Without writing a novel, the carbs must be ballanced using a Synchrometer or similar device.
A book dealing with the carbs is must have item if your going to fool with them. Being such a fool,I have Weber Carburetors by Pat Braden. Tuning steps are in there.
Unfortunately, he talks about fresh carbs and not used & abused ones like most of us have and dosen't deal with stuff like dirt.
Another source of lean pop is clogged idle passages.This is my next step to fix my two reluctant holes. The solution(I hope) is to remove the idle jet and spray carb cleaner thru the passage to disloge any crap therein.
Reading the plugs is a big help in isolating bad cylinders. Plug electrodes(insulators) should be grey, white is lean, black is rich.
I have K&N filters and the top shields undersides show stains(fuel) at the offending holes.
All this assumes the ignition & mechanical systems are right.
I am learning to deal with Webers and certainly don't have all the answers but am slowly climbing the learning curve.
J P Stein