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????
Actually the use of O2 sensors as a tuning tool, is one of the least expensive deals going. Install sensor(s),if can't find boss, use an oil fire ring for sparkplugs, believe it or not the threads are the same (in US anyway ). Use your trusty voltmeter, must be capable of 10 megohms (minimum)impedance, and read voltage. Positive to sensor,start car, sensor MUST be at least 5-600 degrees, lean mixture= low voltage, rich= high voltage.....easy as falling off of a log. Jet for idle,mid range or foot in fan jetting. Nice thing is sensor automatically adjusts for weather conditions or changes in elevation...after all it's only reading the oxygen content of exhaust..while you are welding in bosses, put in a vacuum tap (pipe ) in exhaust pipe also...hook up vacuum gauge and read amount of vacuum in system...higher, more scavanging/efficient, low vacuum giving away HP....enjoy gents
Hi lets keep this one going as my 3000m has just come out of engine rebuild with triple Webers , big valves and a nice warm cam - we've left the stroke and flywheel alone and gone for balancing (uses heavy metal - hope its not depleted uranium - have to see if it glows in the dark!)I got rick wood to set the carbs up but it was some years ago and I'm not sure if he jetted them correctly - incidentally John Wade is well worth talking to - he baffled my sump and it is excellent. It's his copyright so don't ask me for pictures.
Jasper Gilder...sounds like a real nice setup, nice to see folks starting to pay attention to oiling systems, another forgotten performance area, inexpensive also (excluding dry sump systems ! ) Baffles are a sure way to keep the dead dinosaurs where they belong, at the pickup...ANY device that helps control crankcase windage,foaming and pressures is good insurance and a free HP gain. Oil restrictors, scrapers for crank, wipers, louvered or screen type trays, pans with kickouts the list is endless. Look at it this way, at 6000 rpm, how many quarts/liters of oil is ACTUALLY in the oil pan ? Keep it where it belongs and can be used...whats easier, spinning that crank through oil or air ?..not to hard to figure out is it ?
sjam, there is now a very confused panoz!! i have had a quick look and they seem to range from 135/140/145? (thats reading them from the top). since purchase from a circuit race capri i have never used them, a stab in the dark i would guess that they have been bored to the same?
jasper, have you thought any more of hillclimbing yours?
jasper, have you thought any more of hillclimbing yours?
Admittedly for the DCOE, there's an interesting page at:
http://members.aol.com/dvandrews/webers.htm
It sets out the choice of venturis for size of carb/size of engine cylinder, along with formulae to enable you to get a rough idea of main jets, air correctors and emulsion tubes.
I wouldn't expect that a DCNF is too far different to a DCOE or DGAV on the inside. I've used the formulae to get close with jets for the 32/36 DGAV on the Vixen.
Spin
http://members.aol.com/dvandrews/webers.htm
It sets out the choice of venturis for size of carb/size of engine cylinder, along with formulae to enable you to get a rough idea of main jets, air correctors and emulsion tubes.
I wouldn't expect that a DCNF is too far different to a DCOE or DGAV on the inside. I've used the formulae to get close with jets for the 32/36 DGAV on the Vixen.
Spin
ps
Found a page detailing standard fitments of all common Webers and their jets - perhaps the V^ would be like the Dino V6?
see:
www.triumphspitfire.com/jets.html#dcnf
Hope it helps.
Hey panoz - you're taking this too seriously, man. Just think smooth, that's the way to more speed....
Also, lose about 400 of the 2240lb the 3000M weighs!!
Found a page detailing standard fitments of all common Webers and their jets - perhaps the V^ would be like the Dino V6?
see:
www.triumphspitfire.com/jets.html#dcnf
Hope it helps.
Hey panoz - you're taking this too seriously, man. Just think smooth, that's the way to more speed....
Also, lose about 400 of the 2240lb the 3000M weighs!!
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?
You are probably right in that selection of jets is not that complicated! I've not had a close look at a triple Weber set-up but I can imagine that the linkages could be a problem area.
If one throttle plate opens or closes marginally in front of / behind another then the vacuum in the body will change and hence the fuel will be metered in at a different rate.
One easy way to find out more would be to go to a Historic Touring Car race where there are bound to be lots of Group 5 (?) Capris.
Spin
If one throttle plate opens or closes marginally in front of / behind another then the vacuum in the body will change and hence the fuel will be metered in at a different rate.
One easy way to find out more would be to go to a Historic Touring Car race where there are bound to be lots of Group 5 (?) Capris.
Spin
Go for it SJAM the carbs are a good looking bit of kit but there again so are a nice set of injection throttle bodies. If you can't get the mixture right with them then try another engine!! What did John Wade recommend in replacement as a matter of interest? sorry for the late reply but tied up a bit out here as you can imagine! Good thread though lets keep it going.
Edited by mk1 on Saturday 13th October 08:50
Edited by mk1 on Saturday 13th October 08:50
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!.
Message for Panoz - I will try hillclimbing. Ideas on saving weight at little cost and work on the car... try visiting www.weightwatchers.com - off for more lettuce!
I you can get it to splutter down the road you could try a good rolling road place that remembers what a carburettor is. I recommend Aldon Automotive in Cradley Heath near to Birmingham. They did a great job on my MGB that I Hillclimb and Sprint and have just booked my Taimar in for them to set up the new engine now that it is run in. Its got the standard DGAS carb but the engine is 3.1litre with Stage 1 heads and fast road cam.
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