delortto carbs

[norfolk boy]

Hi all,
after much frustration I removed my carbs from car and had repair kits fitted (dlah40) the reason for this was mainly sooting plugs despite adjusting mixture screws but also when getting ready to thermo cycle the engine to free the clutch idling was irratic and also hesitation on throttle.
I am fitting them back on car this evening (+2 130s) is there anything I should do to try stop the sooting? The engineer told me 2.5 turns on the mixture screws though my manual says 2 turns.
any suggestions much appreciated
Simon

[chicagojeff]

i would buy Des Hamill's book, "Powertuning Weber and Dellorto Carbs". It helps a lot.

Mixture screws on Dellortos are much finer than webers, and may take more turns out. Mine are at 4 turns out. It has a lot to do with your progression tubes , and those are swappable.

Also, it is CRITICAL to get the two carbs balanced. It is not easy to do without a manometer, but the book describes a crude way to start. Basically, you get the second carb (one towards the front of car) to just start to get opened by pushing on the throttle rod, and then turn the balancing screw another half turn...

One more thing...the way it works under load and all heated up is tremendously different than when you are playing with it in the driveway. Get it running rough, and then drive around for 30 minutes.

hope that helps.

[norfolk boy]

Thanks for the prompt reply geoff,
I do have a manometer which i do use to balance the carbs, what has suprised me is the 4 turns on the mixture screws, is it more turns the weaker the mixture then?
si

[lotusanglia1965]

There isn't a set number of turns that will work-you need to give the engine what it needs.I find it best to balance carbs and get as low an idle as possible ie not on progression,then screw in in turn each mixture screw till engine runs on three,then turnout slowly out until revs pick up-runs on four. this will be the weakest mixture the engine will run on at idle and hopefully not soot plugs!
cheers,
Martin

[handi_andi]

Probably a daft question, but comes from own experience, have you checked the timing on the engine? My engine was running rough and sooting plugs, turned out only 3 out of 4 spark plugs were working and timing was out by like 20degrees.
Cheers
Andy
PS I am running on same carbs on a 130 engine

[bill308]

In addition to what Martin suggests, the engine should be fully up to temperature, some might say stinking hot, to set the idle mixture properly. The mixture should not be so lean that it misfires occassionally under these conditions, but lean enough that the plugs don't foul at idle on a hot day in traffic.

Bill

[norfolk boy]

Hi all,
well fitted the carbs and low and behold it ran, balanced them up and set the mixture screws at 2.5 turns and 1000rpm and she purred, no hesitation on throttle, I feel am getting there at last!
Have done so much to the car this year was wondering wether i was ever going to get it on the road (lotocones, donuts, valve seats, servo, clutch slave and exhaust) just want an mot now!
Regards Simon

[cliveyboy]

Simon
Sooting plugs is quite common with dellortos. (I speak from experience)
The jet sizes quoted in the manual are not very practical especially when you have a 120 main jet and a 130 air jet.
The 120 main jet is about right although on the standard engines I know that have been rolling roaded they tend to go down to 110.
The air jet is the problem as for an engine (under 2 litre) you would normally start off with a 180 and work from there. A rule of thumb is the air jet is + 50 on the main jet as a reasonable starting point.
I have seen other figures in manuals of 120 main and 160 air jet for our engine which would be more realistic and similar to my carb settings.
Changing the plugs for NGK BP6ES' is also worth doing as they keep cleaner by running slightly hotter
Clive

[zeteclotus]

Avoid champion spark plug they always seemed to go black.

I ended up fitting hotter ngk plugs and lowering the float chamber level by 0.75mm same carbs as you. Now as long as i warm the engine fully every time I start it, the plugs stay clean and runs real smooth for a twink.

I use a colour tune to set the idle mixture.