Mysterious Weber issue on 67S. HELP!!

[RetroSC]

Paul, I did some more checking on the items you suggested. The ball valves on the acc pump jets are seating and the accelerator pumps have good action. I set these to .5cc and tested all throates, which look good.

I completely dissasembled the carbs again and soaked them in carb cleaner then blew out all passages with brake parts cleaner. Nothing appeared to have any blockage and clean fluid came out all orifices.

I checked all the floats, needles, and surfaces. A side note on the floats, I used both the ones that came with these IDS carbs and my floats from my working IDT's. Even suspected the IDS high speed enrichment circuit might be causing me problems, so I temporarly blocked the passage by removing the squirters and mounting my standard tops that don't have the cutout. Same issue.

I just can't figure this out. Here's a video of it running with the IDS's with freshly cleaned plug. Lots of smoke and progressivly runs worse as the plugs foul up. Takes about 2 minutes of running before it just won't run anymore due to completely black plugs.

It's running so rich it doesn't pop or spit at all, just smoke. Normally when I put a new set of Webers on they just pop and spit until you get them dialed in, not these!

All adjustment screws make no difference in the running condition, idle mix, air correction, at extremes either way and it has virtually no effect. I then move everything back to my IDT's, jets, ventirues, floates, accelerator pumps,(everything!!) and it runs fine..... What the heck could be wrong with these things!!

Youtube link:

http://www.youtube.com/watch?v=LKtc6Zn6T0w

[2.70Racer]

RetroSC,

Your Weber problem is not mysterious at all. Think about your comment;

quote "All adjustment screws make no difference in the running condition, idle mix, air correction, at extremes either way and it has virtually no effect." unquote

If the adjustment screws make no difference and the engine is running: the fuel and air must be coming from someplace other than the idle circuit.

So where could the fuel and air be coming from?

The fuel and air is getting past slightly open butterfly's.

Where else can the air & fuel come from?

When setting the idle, the butterfly's must all be closed.

Weber has provided a path for fuel through the idle fuel screw.
Idle air is controlled through passages through the idle air circuit.

Flip the carbs over and look at the butterfly's. All three b-fly's must be closed. With some older carbs, (what Webers aren't old?), it is common for one or two B-fly's to be fully closed while the remaining B-fly is open.

Completely back off the idle speed screw located at the end of the butterfly shaft. There is only one for each 3 carb assembly.

For the idle fuel and idle air screws to have any control the butterfly's must be closed.

If the B-flys are open fuel and air bypass the control screws.

With air and fuel bypassing the control screws, they have little or no control, usually no control.

As I'm sure you are aware, the shafts must not be loose.

Make sure air can't leak past the control screws or the idle jet holders. May need O-rings.

[Fritter]

Are you adjusting at 900 rpm with equal vacuum on all throats using a snail?

Have you checked the jets with a jet gauge to double check size?

Are you sure floats are set correctly?

[RetroSC]

Doug, I guess that's what I do find mysterious about this problem. The butterfly's and shafts on these have virtually no play. All butterfly's line up good and close properly.

Idle isn't really the issue here, it's sort of a nonfactor because this thing isn't close to idling. The only way to make it remotly run is to continually jab the throttle(resulting in black clouds). If you let off it dies instantly, just gets flooded out I think.

I'm no expert on Webers, but this is probably the 5th set I've installed on a car and I've never had an issue remotly similar to this. As stated above, I can move everysingle component back to my IDT carbs and it run fine, has for years for that matter, but the shafts on those are shot and the idle isn't too smooth, hence these new IDS's with good shafts.

The floats are set at the high mark, acc pumps set at .5cc, all jets are known to be correct, 180 airs, 125 mains, 55 idles, F3 emulsion tubes, 32mm venturies.

[pcar9119]

Just a thought, but I had a similar issue last week with my carbs, I had it to lean, so i opened up the idle jets, while doing this, i noticed I had the idle screws turned in so far that the cams were actually engaging the acc pumps at idle, i couldn't get any adjustment in screws like your saying. no matter what i did, I couldn't get the thing run differently because I had the cams firing the acc pumps, take a look at that. It sounds crazy simple but it had me baffled for a day!!!

[Mycar]

This is an intriguing tale with no conclusion, was there a happy ending ??

Regards, Mike... running IDSs

[RetroSC]

Actually there was a conclusion, and I swear I posted it years ago.. but it appears to be gone. Anyhow, it turned out to be the idle air jet holders. Apparently different webers used a different screw, some with a raised seat, others not, almost like a washer/spacer on the seating face. Basically I had the wrong screws with the extra material thereby not allowing the idle air correctors fully seat. Surprised not more folks have run across that before with all these Webers floating around.

Totally baffling at the time.

Bill

[Mycar]

Thanks Bill, I didn`t expect a reply so soon on a three year old thread.

I`m in deep search mode, started hours ago, looking for info on spitting carburetors mainly 356 Zeniths but taking in 4 forums and getting endlessly waylayed on the way.

I do recall the the air jet holders been mentioned elsewhere but I couldn`t say where... or when.

Cheers for getting back to me,

Mike.