Calling all Carb experts
Discussion
Hi guys - I'm a new member. Astounded by the technical knowledge that appears to be knocking around in this forum, I have a query that I hope someone can help me with.
I recently purchased a triple weber Essex manifold and a set of 42DCNF's that I'd like to slot into the Taimar I'm rebuilding. The carbs are in good nick, but I have no idea how to jet them for the Essex. The Weber Haynes Manual gives all sorts of spec's for original equipment applications (Aston Martin etc) but not for the Essex.
If anyone has any experience of this I'd love to hear from you. In return, I'll try and help others with lessons learned from the rebuild so far!
PS. Hope you're well MK1.
Thanks for the number - I'll give him a try (I wanna have some fun but try and stay above 10 MPG if I can!).
Out of interest, when you're jetting a carb, do you base it on expected power output or engine size/maximum revs?. The latter I can estimate, the former I'm still dreaming about.
Hi Panoz, I've gone for all the standard Essex conversions, steel timing wheel, big valve unleaded heads, Yella-Terra Rockers with screw in studs etc. I've also gone for less-sensible stuff like RS Williams (ex. Swaymar) steel flywheel, and an AES 'stroker' conversion mated with a +60 thou. overbore which takes the capacity up to approx. 3400cc - bit of an experiment but time will tell. I want to keep the car normally aspirated despite test driving 'MK1's scary (but fun) turbo down in South Wales.
As far as the fine tuning is concerned I'm getting Lambda sensor bosses welded to each exhust manifold on one side so that I can set up each carb indepedantly using a Lumenition air/fuel ratio meter. Before driving I can connect to a boss in the combined exhaust flow and hopefully monitor the on-line mixture in the 'cockpit'.
The 42DCNF's I've aquired have 70 (coarse) jets and 3.5 main venturis. I'd be very interested to know what you're fited with and whether you've used them in anger yet????
Thanks for your help guys. I've been V busy, but spoke to John Wade yesterday about the triple webers, and he had one piece of advice for me - sell 'em! This seems to be based around some years of experience trying to set them up properly.
Rather disappointed by this response and with a refusal to take advice from those vastly more experienced than myself, I'd still like to have a go.
From an airflow point of view, once the manifold is matched to the carbs and heads, this has to be the most efficient air flow pattern into the top of a stock Essex v6 engine (no splitting of flow or right angles etc).
From a closet boy-racers point of view I can't imagine anything nicer to greet you every time you lift the bonnet than a stack of three downdraft carbs on top of your engine!.
So what I now want to know is, what's so tricky about setting these up? - with the Lambda sensor and bosses, I should be able to tune each one on the drive to a sensible mixture at mid-range revs and then observe what happens when I'm cruising or boot it all the way to the top. If the mixture turns lean when I boot it, I'll need bigger accelerator jets - if its horrendously rich at low revs then I'll need smaller idling jets (or I can sit it on the drive again, get the mixture right when idling and repeat the process).
Any comments?
Rather disappointed by this response and with a refusal to take advice from those vastly more experienced than myself, I'd still like to have a go.
From an airflow point of view, once the manifold is matched to the carbs and heads, this has to be the most efficient air flow pattern into the top of a stock Essex v6 engine (no splitting of flow or right angles etc).
From a closet boy-racers point of view I can't imagine anything nicer to greet you every time you lift the bonnet than a stack of three downdraft carbs on top of your engine!.
So what I now want to know is, what's so tricky about setting these up? - with the Lambda sensor and bosses, I should be able to tune each one on the drive to a sensible mixture at mid-range revs and then observe what happens when I'm cruising or boot it all the way to the top. If the mixture turns lean when I boot it, I'll need bigger accelerator jets - if its horrendously rich at low revs then I'll need smaller idling jets (or I can sit it on the drive again, get the mixture right when idling and repeat the process).
Any comments?
Hi MK1. It's your block they're going to sit on - will you give me a refund if they don't work!
John Wade sounded like a really knowledgable bloke, but came across a bit miffed that I'd not come to him for the whole engine and as he put it, he 'doesnt like sorting problems for people who didn't come to him in the first place'. Anyway, he recommended a well set up single Weber 40 rather than the triple 42s, although he did say that if you can get the 42s set up well they'll give you a nice kick at mid range revs - don't really understand the reason.
The one thing I have learned from this string is that as with alot of things, the carbs need to be setup according to the spec. the engine, and there is no standard setup even for supposedly identical units.
Spin, yes I thought the same about the linkage so I've made one based around two threaded rods with locknuts so I can adjust the spacing of each link and set them to pull identically. My other concern (not knowing the history of my secondhand carbs) is that one may not be as 'tight' as the others and there may be slight differnces in response. I would hope they wouldn't be that sensitive!.
John Wade sounded like a really knowledgable bloke, but came across a bit miffed that I'd not come to him for the whole engine and as he put it, he 'doesnt like sorting problems for people who didn't come to him in the first place'. Anyway, he recommended a well set up single Weber 40 rather than the triple 42s, although he did say that if you can get the 42s set up well they'll give you a nice kick at mid range revs - don't really understand the reason.
The one thing I have learned from this string is that as with alot of things, the carbs need to be setup according to the spec. the engine, and there is no standard setup even for supposedly identical units.
Spin, yes I thought the same about the linkage so I've made one based around two threaded rods with locknuts so I can adjust the spacing of each link and set them to pull identically. My other concern (not knowing the history of my secondhand carbs) is that one may not be as 'tight' as the others and there may be slight differnces in response. I would hope they wouldn't be that sensitive!.
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