Weber 40 DCOE Carb Setup???

to be honest its best set up on a rolling road as they will get it spot on for you. You will get a load of advise which will only confuse you and may do more harm than good. It will cost a few quid but in my view its money well spent, you should even get a power print off too if thats what you want but make sure you tell them its a new engine and the spec of it too

From what I have read you should not drill the jets on either Weber or Holleys since it is very hard to mimick the smoothness of the correct jets.

As above though a rolling road who is familiar with Weber DCOEs should see you straight .

srun is slow running/idle jets . the F number is the air bleed and the first number is the fuel orifice size. not all various size slow running jets are available anymore so they may have to resort to soldering and drilling. as long as care is taken in the drilling and cleaning up the burrs then drilled jets are fine.

driveability is always the hardest to set up and can be a lot more than just changing jets. auxillary venturies are the 'sensor' for the fueling so different size ones of these can be used to make the progression more or less sensative as required.

float height will also have a profound affect on slow running and progression. book setting may not be the ideal but it'll be the place to start. raising the float height will make the main jets come in slightly earlier if it goes weak on progression etc but it'll make virtully no difference on full throttle. even modifing the progression holes can make a difference to driveabality, thats why certain carb part numbers work better on some engines rather than others. i think the prefered carb for Ford engines are DCOE9's? but by cunning modification any carb type can be made to work.

what you have will be fine to start with because you need to start somewhere. F11 on the emulsion tube rings a bell on Ford engines but i wouldn't worry until the engine has been dynoed to see what the fueling does.

40's on your engine once set up should be a good compromise between having good low end power and just sacraficing a little power at the top.

can you update the thread with what the tuner finally ended up with so anyone else searching will have a bit more info to work with . cheers

Bozwell, sorry to correct you but the F number most likely relates to the emulsion tube number - here an F16 which is correct for this engine type/spec (and a bit pricey if you have to change it)

the 'air' number refers to the air corrector, which affects the mixture at high engine speed

Just wanted to avoid any confusion

Agree totally barty!

i've got a xflow powered westfield with 2 x dcoe18 40s - best source of reliable online advice I found was the blatchat site (caterham owners) and the wscc boardroom (westfield). Lots of guys on there are/were running these carbs on xflows/pintos/zetecs/XEs/BDs etc and there's some great guidance there.

I really struggled to find a garage/rolling road that really knew how to fault find and tune these so I ended up reading the speedpro book and the haynes book and got to the point that I can happily work on set of dcoes, they're actually very straightforward to work on. The dave andrews jet program gave a very good starting point for the jets on mine too which were waaay out when I first bought the car.


edited to add - con2k, do you have a fuel pressure regulator fitted with your electric fuel pump? if not, you should invest in one - dcoes don't tolerate a fuel pressure much over 3psi and most electric fuel pumps put out more than this, eg facet red top.

Bozwell, sorry misunderstood which F number you were referring to there! Agree totally with what you say.

i didn't have much luck with 45F9 idle jets on my 1600 xflow (A2 cam), they caused the engine to spit back occasionally at low engine speeds, it was much happier on the 50F9s

Some fascinating information there, just some details to help from me:

I've had a car put on rollers. Not this one, just a standard fuel injection car. So a carb 'setup' will be a new experience from that point of view.

The car is a project. The engine is built up and now the carbs, but combining the two, cable linkages, fuel lines (vaccum hoses?) etc are not. Once the shell is painted and the engine is fitted and run in, I will definately update this thread with the details of Power, torque and any changes made.

Yes the car did run and will run a fuel pressure regulator. an FSE unit was removed and will probably be refitted.

As seen in the picture, it says the main jets have been drilled. This could be the current rebuild guy, or a previous person. I was not told which.

Westy, checking those links out now. The engine spec is very similar. But the higher lift 244 cam means it's guna be pretty poor low end anyway I'd have thought. Will a good setup help with low end if setup in such a way? The roger king spec has 130 Main and 140 Air compared to my 135 Main and 155 Air. (I wouldnt know at the moment with my current level of understanding, if this is a big difference). Then again, it's a different engine, different cam and variations in build quality/experience/understanding are bound to vary the reason for these settings.

The carbs are 40 DCOE's. A pair of '40DCOE 28' - non sequential serial numbers. About 2000 units apart I think. I don't know how to initially set them up at all. I told the guy rebuilding them that I had no understanding and it was new to me. I wanted them to be suitable to run in my cam for 20m mins without bogging down or being lumpy and then I can look at how they run more accurately on the drive.

Bozwell, your right in saying I wont be fine tuning the carbs myself. Atleast not initially. Maybe once I get my head around it ALOT more and alot later. So a High Dur. cam and Low comp engine aren't a great combo. Depends how High/Low mine is. The 244 comes in quite late and the 1300 pistons decrease the compression I think as they are bowled instead of flat topped (ignoring valve seat cut out requirements). A common level of specification (In fact I think the riginal engine work was carried out by Vulcan Engineering, but back in the mid 90's and approx 8 owners since then. Who knows what happened between then. All I remember is the car revved very high for a kent xflow and was nothing, nothing, nothing then really really lairy.


I think my best bet is to do some furhter research into the variations and then I'll have a better understanding of what I should expect. Unless someone comes in and tells me the DCOE28 versions are completely wrong for my engine? - I'll be fairly disappointed after paying out for the work, but would assume the jet settings I was provided with are the reasons for the Version numbers and are now matched to the 1640 xflow.

Many Thanks to all.

if you tried both of these combinations one after the other and watched the mixture through the range at full throttle i would say the only difference would be slightly leaner at the lower part of the rev range for the 130main and 140air. the mixture at the top part of the rev range should be about the same for both settings. why is this you ask?

i'll try to explain so when you see what the tuner is doing it'll hopefully help your understanding of what is going on.

if you only had a main jet in a carburettor, as the rpm rises the mixture gets richer and richer due to the higher air flow increasing the venturie affect. to stop this from happening air is introdued to 'slow down' the fuel. that is the job of the air corrector. the emulsion tube then allows the air to bubble/froth the fuel to make it ligher so it reacts quicker at rpm changes.

say with your 135 main and the 155 air the mixture was very rich at 3000rpm but good at 5500rpm. to lean off the fuel at 3000 will need a smaller main jet, but this will lean through the whole range which will hurt the top end. to richen the top end back up a smaller air corrector is fitted to lessen the braking effect of introducing air into the mix. with me so far?

with a wild cam you will need loads of fuel at the top end. but this will probably make the bottom end too rich to even run properly. to over come this it may be nessesary to fit a smaller main jet but go way down on the air corrector. something like 125 main but a 100 air. (mains are small jumps in sizes and airs are big jump in sizes) you should be able to work out what this affect it'll have

emulsion tubes will also help in changing the mixture through the range because they have different hole positions to bubble the fuel different amounts at different rpm ranges. for example an F7 is a lot more sensative at lower rpm so will be richer at the bottom and an F11 is leaner at the bottom end, irrespective of what jetting you use. F16 is about middle of the range. these take a lot more experience to know when to change them.

so that was just the easy main circuit, but what about progression? at the flange end of the carb there is a little brass plug above each throttle. if you remove this plug and look down the hole you will see drillings. these are progression holes and each hole works to pass fuel from the idle jets. as you just lift the throttle to say 1100 rpm the butterfly will uncover the first hole and as you increase to say 1200 it'll uncover the next and so on (usually only 3 holes). by 1500ish the main circuit should just start to come in. for different carb types they are usually in different positions and for 16valve engines they usually have 4 progression holes.
so the first step would be to set the idle mixture then open the throttle a tad to see what the mixture does. if it goes lean then a slightly larger idle jet is required so fit new jet, reset the idle mixture and raise the throttle a tad again.
what if that is all now fine but as you open the throttle more it still goes to lean. you could try an idle jet with the same size drilling but a smaller side air hole (does the same as the air corrector on the main circuit which you should hopefully by now know exactly where this is going) fingers crossed the mixture at progression is now good. you shouldn't need to touch the progression holes but if there is still a problem then raise the float height slightly to see if that richens the progression. if not then drilling the progression holes very slightly (or even adding a fourth) may be the only answer. BUT there is no going back so if it goes wrong it'll be a pain to sort.

many years ago i had an Aston martin DB6 with Webers on the rollers to sort progression as no one else was able to sort it. after trying every idle jet combination i got the micro drills out and drilled a fourth progression hole slightly larger than the rest. it worked ;D . i had to put a large idle jet in to resort the mixture but the difference was amazing. the owner came back a week later very happy to tell me it had also gone from doing 9mpg to 15mpg.


anyway, with a big cam at low rpm the engine is very ineficient so you can actually run a lot more ignition advance at the bottom compared to a standard engine than you think. once your engine is running it'll be worth making an ignition advance graph to see what is going on. take an ignition timing reading from idle and every 500rpm from there.

so

idle 10 degrees
1000 rpm 10 degrees
1500 rpm 14 degrees
2000 rpm 18 degrees
2500 rpm 24 degrees
3000 rpm 28 degrees
3500 rpm 35 degrees
4000 rpm 35 degrees
4500 rpm 35 degrees
5000 rpm 35 degrees

only as an example.

max advance is usually around 3,500ish. you may find the engine likes 28 degrees at 2500 rpm but not like more than 34 at 3500 rpm. it'll be trial and error but can make quite a difference to how the engine performs at the lower rpm ranges.


hope it all goes well for you as carbs once set up can wok really well. it's just finding someone who will go the extra and not be afraid to do more than just change jetting.

problem with jets are that they cost about £8 for four so a few sets will end up costing a fair bit when you only need one set. a rolling road set up for carbs should have quite a few jets in stock but they don't always have everything because it's £thousands tied up in jets, chokes, emulsion tubes etc.

best bet would be to buy a set of micro drills and a drill holder plus a soldering iron. that way you can experiment with any number of jet sizes and once you have the combination that works buy that size new.

This Four Stroke Performance Tuning book is well wort buying as it goes into loads of detail about every aspect of engine tuning for example there is a section on exhaust manifold design with ideal primary sizes/lengths etc and goes into good detail on how all the different collectors and mergers affect power.

a carb syncrometer is about £30 but it'll be a good investment as the carbs will need a little tweak every now and then. it makes that job so much easier. probably find after a few goes setting up the balance and idle mixture you will just be able to get it right just by the sound alone.