If it's any help, if the Weber "stumbles" you mention amount to a huge, off-idle flat spot, the usual cause is a lack of sufficient progression holes. The only solution until now has been to run the idle circuit massively rich to try to compensate for initial off-idle leanness, just to get it to run at all. Most have found that, once they're off the idle circuit (say, 3,000 rpm or so), it all works fine. Or, at least, it's easy to tune the main circuit to a proper stoichometric mixture.
It seems that engines with very sudden vacuum changes (large throttle plates, short intake runners, 4-valve DOHC heads, etc.) are the most susceptible to this condition. I'm running a Zetec, with a manifold with only 2" runners. The conventional wisdom in the UK (where such engines are common in Locosts) is that more progression holes are essential to cure this problem. The holes can't simply be drilled, willy-nilly, without totally destroying the carbs' effectiveness - they must be absolutely precise in size & location. We're talking .0001" accuracy here.
All sorts of different solutions have been tried, using every Weber part available, dyno testing, etc., with an absolutely zero success rate.
The Alfa aficionados in Europe have started using 4-progression hole 45DCOE's with some reported success. However, the Zetec, which apparently breathes much better (i.e., a much bigger gulp of air at the slightest throttle opening, due to it's extremely efficient flow characteristics), needs more.
To that end, Weber, in concert with Webcon in the UK, have designed 5-progression-hole DCOE's specifically to cure this problem for the Zetec, and it's anticipated it may be the cure for other engines with similar carburation issues. I just bought a brand new pair of these 45's from Webcon, and expect that I will be free of the off-idle stumble (in Zetecs, this is reported to be so bad that they backfire, buck, & often stall completely, at the first millimeter of throttle opening...unless the idle circuit is blubberingly rich). The extra progression holes (standard 152 series 45's commonly only have 3 progression holes, but it seems 5 are required) supposedly smooth the fuel delivery so that the idle circuit can be kept nice and lean, yet supply all the fuel needed for proper progression all the way through the idle circuit.
Here's a link, if you're interested:
http://www.webcon.co.uk/shopexd.asp?id=15161Just a thought....
_________________
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/
Login
Register
FAQ
Members
