Spark Plugs Sooting Up - Mixture Too Rich?

[4129R]

I have at last got 4259R on the road, after it has been in bits for 20+ years.

I road tested it, and after about 20 minutes normal driving, the engine started coughing, and then cut completely.

After a while, I took the plugs out (Champion N7Ys set at 25 thou gap) and they were all matt black. I fitted clean plugs and got it running again to get the car home.

I am running Weber 40DCOEs. I have now put in 31mm chokes (for maximum power at 1600 rpm for a 1600cc engine) 120 main jets (recommended 4 x the venturi size) , 175 air corrector jets (recommended + 50 the main jet size) F11 emulsion tubes, 45F9 idle jets, 40 pump jets. The mixture screws are out 1 1/4 turns.

Any suggestions on better jet settings, or how else to weaken the mixture? The book says 4 x venturi size for main jets = 115-125 main jets,  +50 for the air corrector jets = 165-175. If it still runs rich, should I increase the air corrector to 200?

I set the floats in both carbs to the correct clearances (7mm touching the ball valve, 16mm fully down).

http://lotus-europa.com/manuals/misc/carbs/carbs.htm

[BDA]

You might discuss your problems with Keith Franck here: https://vintagetechnologygarage.groups.io/g/sidedraft. He probably knows more about Webers than anyone.

I’m not saying that your fuel level is wrong but I prefer to measure it in situ by taking out an emulsion tube and with the fuel pump running or shortly after shutting down the engine, measuring the distance from the ledge where the tube is screwed in to the fuel (https://www.youtube.com/watch?v=meaGMoH4Pmw). It should be 25mm.

[SwiftDB4]

I agree with BDA. Measure the depth with the emulsion tube out idling. Should be 25mm. Just measuring the float with cover off doesn't account for leaking needle valves or excessive fuel pressure among other factors.

[Clifton]

.025" is pretty tight on a plug unless it's turboed or supercharged.So

A wideband is really the only way to know where you are rich or lean. I used mine on a Honda SOHC bike to get right. No way I could have guessed.

https://www.amazon.com/AEM-Wideband-Ratio-Sensor-Controller/dp/B01FEH2GNW/ref=pd_ci_mcx_pspc_dp_d_2_t_2?pd_rd_w=d2ho0&content-id=amzn1.sym.568f3b6b-5aad-4bfd-98ee-d827f03151e4&pf_rd_p=568f3b6b-5aad-4bfd-98ee-d827f03151e4&pf_rd_r=A4F2617RWMAT8QXHSV6P&pd_rd_wg=yCmr0&pd_rd_r=b58c70fc-5314-48e0-acda-c3cb513fe9fc&pd_rd_i=B01FEH2GNW

[jbcollier]

All the calculations and set-up you used are to get a ROUGH starting point.  You ALWAYS have to tune after that.  What engine and level of tune are you using?

[4129R]

All the calculations and set-up you used are to get a ROUGH starting point.  You ALWAYS have to tune after that.  What engine and level of tune are you using?

Federal spec cams, gas flowed head, free flow exhaust, probably producing 125 BHP.

[EuropaTC]

Why not start out with the Lotus S/E or Sprint Cam settings ?  Otherwise I'd say that Keith Frank's group is the best place to ask this sort of question, as BDA says, the guy has dedicated himself to understanding and improving this type of carb.