Reviving an old "necro-post", here.
Further to my earlier rant about progression holes on 45 DCOE Webers, I've continued to do research (for yet another year), and have learned a few things about the massive, overwhelming stumble that occurs on DOHC 16-valve engines with them.
Apparently, the breathing of the newer DOHC engines is sufficiently good at low RPM's that, without modification, current "Series 152" 45 DCOE's can't supply enough properly-metered fuel to keep them running properly. When the butterflies are first cracked open a tiny bit, the carb throat "progression holes" are gradually & consecutively uncovered by the edge of the throttle plates, allowing fuel into the airstream. These holes, (3, in current model 152 45 DCOE's) simply aren't up to the task, and the engine will run hugely lean.
Up until recently, the "cure" (a Band-Aid fix, at best) was to use enormous idle jets to flood enough fuel into the carbs to keep the engine alive.
Optionally, you could have your existing carbs drilled for extra progression holes...but, this requires the services of a master machinist, experienced in this modification, and equipped with a special jig (no longer available anywhere - I've checked!) & milling machine. As for trying to do it at home, well, good luck with that!
Unfortunately, these carbs run on the "idle circuit" all the way up to between 3,000 and 3,600 RPM (so, "idle circuit" is clearly a misnomer), which comprises the majority of driving outside a race track. Even with massively oversized idle jets, there's a stumble (and sometimes even frequent stalling), clouds of grey smoke from unburned fuel, and horrendous fuel economy overall (think heavy truck, big block, full throttle fuel economy), not to mention trying to ignite all that fuel. There has to be waaay too much fuel all the way through the circuit, just to ensure there's enough available during the moments that the engine needs it.
There are now, however, 152 Series 45 DCOE's with extra "progression holes" in the carb body throats to help combat this issue. You can buy 152 "G" model carbs now, which have 4 progression holes per choke, and these apparently will solve the issue, for most engines anyway.
The Zetec (the engine I chose, of course!) is, it seems, spectacularly susceptible to this problem, and the "G" model 152's only go partway toward solving it. To that end, a company called Webcon in England (which pioneered the fitting of Webers to Zetec engines) came out with special, 5-progression-hole carbs, specifically for the Zetec. Purportedly, these carbs will actually CURE the problem in Weber-carburated Zetec engine, once and for all.
As there's likely no way I'll ever get my 3-progression-hole 152's to run properly on my Zetec (if I could, I'd be the first one, in 20+ years of trying & failing by experts), I'm negotiating with a company in England to purchase a set of the 5-hole Webcon carbs at a price that doesn't look like my mortgage payment.
We'll see - as I anticipate plenty of other variables to deal with in getting my engine to run, I'd really like to eliminate as many as I can. Having carbs that should work, right out of the box, would help a lot, I suspect.
_________________ Scratch building, at continental-drift speed, a custom McSoreley-design framed, dual-Weber 45DCOE carburated, Zetec-engined, ridiculously fast money pit. http://zetec7.webs.com/
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