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Progression holes

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Hi 02ers, I've got a 32/36 DGEV on my 02, and I've always had an annoying stumble at about 2-2.3k rpm and slightly rich running. I always thought it was the jetting, but rejetting to CD's specs and a rebuild kit didn't help as it still stumbles at 2-2.3 and runs a bit rich. Today I had a closer look at the carb and found that one of the progression holes is significantly bigger than the other, and also a small extra hole has been drilled slightly upstream of the other hole. So I plugged the small 3rd hole with JB Weld, but don't know if I should somehow close off some of the larger hole as well. It does make sense to me that this is my problem...both running rich AND stumbling at that rpm because of too much fuel coming through the progression circuit. Also I've pretty much eliminated the basics: jetting, float level, vacuum leaks, etc.

So my question is, is that second hole meant to be that large? Anyone want to compare progression holes??




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Guest Anonymous

Well before I ever heard of CD(Sorry he sold it!)'s formula, I tried something similar except that I used solder for the progression holes. I found the exercise to be futile in that despite my effort to approach things scientifically, each time I refitted the carb I would notice an entirely different operational quirk. Some of these quirks were remedied by timing and spark plug changes including something as simple as a larger gap or warmer plug. I had been ultra sensitive to flat spots or progression issues and even resorted to a dyno and an exhaust gas analyzer which was made available to me by a shop that set up Porsches.

I kept notes (which I have not been able to locate along with my hundreds of jets) so I am working from memory. CD's recommended jetting setting is ok for a start, but I agree it is not necessarily the best setting for all 32/36's. There are two things you did not mention that I found could have a dramatic effect on progression: emulsion tubes and float setting. I recall from a few dyno readings that the lower rev power curve was changed enough to account for progression issues by changing the emulsion tubes two or three steps.

Look at the other boards that use the same Weber carb (Datsun 510, MGB, Ford Cortina, Audi and VW). Pay careful attention to the emulsion tube recommendations and go from there. Just because your carb came with a middle-of-the-road F11 or F50 doesn't mean you should stick with them. In a perfect world, you would have many versions of the same carb to swap and test.

If you look at the BayArea02 article (search the archives) on setting up these carbs you will find a WIDE disparity of "expert" opinion on jetting, emulsion tube settings and even manifolds. The only one's that are correct are the ones with proof via the dyno, racetrack or your billfold.

You may recall the expression: when in doubt, lean it out. If you are on the leanest edge, you will likely experience progression problems. One of the things that manufacturers tried to overcome this issue is substantially widening the spark plug gaps. Of course they also went to much better electronic ignition systems to ensure reliability. If I were you, before I tried anything else, I would try widening the plug gaps to .035 - .040 or even wider. Its easier than trying to locate Weber parts.

If I locate my notes I will attempt to supplement this post. If you achive any measurable success, please post your results. (I am rebuilding an MGB with very worn SU carbs but I am considering using the Weber.)

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Thanks Hector, my plug gaps are on the small side so I'll open them up to see if it makes a difference, I'll look into the other things you mentioned as well. I'll also probably take it to a Weber guru and get him to look over it, and if necessary get him to close up that large progression hole a bit, hopefully without having to remove the throttle plates and causing more problems...

If I manage to fix it without swapping over to another carb body I'll post the results. Thanks again for your input mate.

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