OK
sounds like you have it right
that fella on the link you list has his head screwed on
do you have the suggested emulsion tubes F6? if not it will never work....i promise i went through this with mine.......
i'm trying to feed a 700CC cylinder with a cvarb designed for 400cc to 500cc Cylinders on a 2 litre 4 or 2.5 litre 6 and mine is a 4.4 litre 6
do you have the 120 140 or 150 needle jets
set the float height with an 8 mm drill bit between the lid and the float. its the easiest way, ideally you set float height with 1 tab and you need a setting for float droop and get that right as well.
8 mm from the lid rather than 6 alters how hard the needle jets will be pushed when closed. sounds like a bodge, but presume he caters for it with his jetting and emulsion tube suggestions
the rest of what he says makes sense to me when i think about my own weber DCOEs i think following his lead makes sense
you will not get anywhere if the BOLT IN configuration is not right
emulsion tube tailors the delivery across the range from about 1200 rpm up to redline and the main jet makes it rich or lean to a certain extent across that range, this is your fuel air profile across the range
idle set up
new set of cheap plugs get 2 sets
and a decent set for REAL you don't need to spend lots just get branded plugs don't need no daft platimum multi contact shennaingans
NGK or bosch or champion if buying in a box rather than a plastic bubble pack... there is a reason most sell em in boxes, they don't get busted when they are thrown from the delivery truck someone tell champion.
it needs to idle well but the mixture needs to be "fat" enough to get you over transition from idle onto the main circuit
he seems to cater for that with a 1 size fits all....if you can get away with that no issue. when i stuck dells on mine idle jet was the onlything i changed.... horses for courses.
best way to tune the idle is initially with a timing gun so you can see rpm increases as they happen, rpm will labour up an down, note the peak if it swings 900 rpm to 915 rpm, and you make a change that consistently sees apeak 920 rpm even though it still stumbles back to 900 thats your rpm increase.
you are edging slowly towards "nice" the path there won't be smooth.
get it running
get them balanced, same opening per carb, linkage off, use feelers use airflow meter whatever
turn idle mixture screws in to zero than out exactly 1.5
get it running 1.75 turns if necessary.
once balanced REMEBER wind in or out each throttle stop screw the same on both carbs to get it ildeing away just a tad faster than normal if normal is 850 run it at 900 rpm to help keep plugs clean while tuning
tweak side to side till it stops wobbling about
then get the timing gun or rev counter on it. wind out 1 mixture screw 1/4 of a turn. if the rpms increase good. if they don't turn it back
turn the other the same if they increase leave alone and return to the other side
try again this time the rpms will probably stay the same but it should smooth out i.e the max rpm you see stays the same but the lumpering up and down range gets smaller
if no use
try turning them in
try 1/8 of a turn
you want to hear/see the idle speed increase that you get when the idle mix is right this is like a shallow hill with a steep peak for the top
no good, no good, no good, excellent no good, no good ,no good. we don't know which side the hill you are on and it will be within 1/2 a turn on the ilde mixture screw
wait till it settles each time
and give it a big rev every few minutes and let it settle to clean off the plugs pull both carbs equally to avoid popping and farting and gumming up only 2 of the plugs
youare looking for the highest RPM with the samllest throttle opening and the least amount of idle mixture for smooth running
if the motor is rocking carb balance and or idle mixture between sides could be better....
or you need to up the idle speed
you should be able to get it to idle at 800-900 rpm with any sane road cam
if all else fails use a gunson colour tune £20 well invested, but on a bug you will need a makeup mirror to see what you are doing with your new glass bodied spark plug
connect up linkage
you should hear no chage to idle
likange should be attached and adjusted so it is loose at the drop links with the throttles on their stops
and JUST tight enough to activate both the instance the centre pull pulls.
Alternative
by all means use 1 carb throttle stop to adjust both letting the linkage take the strain of conrolling idle position of the second carbs throttle plate, balance them up by adjusting linkage length on the side that is the dependent carb
just a different way to achive the same outcome
BUT only do this with a CB performance style hex bar that mounts between air filters, you can't do it with an empi swivel set up and i'm not a fan of a fan shroud mount set up becasue the shroud can move indepently of the carbs if things are not done right.
Once happy adjust idle speed back to normal from your slighty elevated 900 rpm remeber depending on how you set up the linkage this may involve just 1 throttle stop screw or both...
this is his ball park, if you are not working with this you have probably answered your own question
1600/1641cc
145 mains, 165 airs, 55 idles, f6 emulsions, 150 needle jets. although he recons 120 or 140 are better needle jets in this application
id buy 2 145 mains 2 150 mains and 2 160 mains
F6 Emulsions
i usually aim for + 50 on the air corrector but my carbs feed 1 cylinder per carb barrel, yours have to cater with pulses from both the cylinders they feed, disruptiong their "day job" rather than just one.
there must be a reason for him going only 20 up and its probably this id buy 155 165 175 air corrector jets
they richen or weaken mixtre across the range but a bigger air corrector will make it leaner at high rpm and cause the main circuit to start earlier at low rpm bigger airs make it easier to drag fuel in from the emulsion tube well at lower RPM.
think of them scewing or pushing a fule air profile vs rpm graph 1 way or the other, tweking 1 end leaner and the other end richer without too much change to the overall shape
think about it the air corrector has a bigger hole so the fuel under it is exposed to a greater weight of air above it (to the edge of space) pushes the fuel in the emulsion tube centre down more when its under vacuum from the running engine than the fuel outside of the tube sitting in the bore, you get a greater mismatch betwen fuel levels IN the emulsion tube and OUTside of it when its all sealed up down its hole. so it alters the bubbling/mixing charcteristic, tuning your emulsion tube fuel air mix profile dependent on vacuum
Its a pig to do
you only know you can do it once you try
once you get it right you can't understand how you could get it wrong so much before hand
Look up David Vizzard Emulsion tube comparison to holley meetering blockset up. explians how they work and why the two companies just did the same thing but with different parts acting on different mixtures of fuel and air
They might be leaner at 8 mm in theory the level in the bowl is lower BUT not if modern needle jets are leaky old junk.... he is catering for the drip drip drip... or weber spain in their infinit wisdom did something daft with the float size/mass/dimensions LIKE they did on the DCOE. i.e he doesn't know why he has to do this but there may be an easy answer, It might not be the needle jet quality. It might be modern floats differeing from the Transit and bedford van floats of yore which will have been soldered spun brass hemispears.
8mm could be the new way you can try Webcon and ask is 8 mm the setting on NEW ICTs when 6MM used to be the setting for OEM ICTs
i.e. have your spanish minions made a another change for the hell of it (don't say that)
if they are in a good mood they will tell you, if you spend some money they may well become quite chatty
if you buy stuff off ebay get it all from the same place, genuine weber is best but eastern European copy stuff aint bad just don't mix and match
infact the ENTEK EMPI JINLIN FAJS stuff from china isn't THAT bad you just have no comeback, if you get some rubbish friday afternoon "after lunch in the pub" jets or stuff that went out the backdoor of the factory.
Dave
