40 DCOE jets - help please.

[4129R]

I have spent ages doing the finishing touches to 2520R, but I cannot get the engine to run smoothly above 2500 RPM.

The engine is fairly standard, 10.5:1 compression, with Federal cams, and a gas flowed Weber head.

I have set the 40 DCOEs with 31mm chokes, 120 main jets, F11 emulsion tubes, 180 air corrector, 45F8 idle jet, and it runs really rough.

Is it just a case of twiddling the mixture screws or have I got the wrong set-up.

I had tried 130 main jets, F16 emulsion tubes, and 170 air corrector, it ran rich with black plugs, and back-fired when the engine was turned off. My wife thought I had shot myself !

Can someone tell me the correct jetting for around a 120-125 BHP fairly standard engine with federal cams please?

The timing is set by strobe to around 22 BTDC at around 2250 revs.

Otherwise I have just about got the car fully restored after many man hours and much deliberation when things didn't work.

[EuropaTC]

Without digging out the manual, is 31mm the right choke for webers on those cams ?

When I had my Elan with S/E cams, supposedly 115bhp (or 118 depending on the road test) they had 32mm chokes.  With standard sprint cams/valves they went to 33mm and I changed jets to suit.   

Just having put Vegantune VJ5 cams in the Europa the Dellortoes  are now on 33mm chokes. I can't recall whether I went for the standard BV jets or not, but I do have some notes from Ed Winter where he said the VJ5 worked well without changing the carbs. It's relatively early days and I have no idea what it's like at the rev limit but it's certainly smooth delivery from tickover to 4-5k revs, no stumbling or apparent hesitancy once warmed up.

Brian

[4129R]

The mixture is way off at the moment. It is un-driveable. I need to know the whole jet set up, so I can start with something which is known to work.

[EuropaTC]

If it's that bad, why not start with the standard sprint spec and 33mm chokes ?  PDF added from the Elan manual, my Elan is on Sprint cams with this setup and I reckon it's smooth enough.

Brian

[jbcollier]

You are changing a lot of stuff at once.  Very hard to judge changes when you make a lot of them at the same time.

Federal cams are milder than Sprint cams so I would use the std Elan set-up as a starting point.  I suggest using the Elan set-up  (E-TC posted above) as they used Weber carbs rather than the Dells the Europa used.  That should settle your emulsion tube and choke choices.

Are your carbs clean?  Float levels set by the book? (yes, there are alternate methods but start with it by the book)  Did you check the valve adjustment?  Compression?  Timing?  Timing advance?  Wires, cap, rotor?  If everything is good, then you can work on the carb jetting.  Before that, NO.  Fix everything else first, then jet.

What kind of DCOEs are you using?  DCOx-xx?

[dakazman]

   4129R
 You’re probably past these reference books , I posted here :

http://www.lotuseuropa.org/LotusForum/index.php?topic=2058.1395

  As a novice they all help me understand the internal functions and if someone searches for your topic they will be in one place.

  And this link:  4129R see chapter 4

https://240260280.com/Tech/Carbs/Weber/docs/Hammil/Power%20Tuning%20Webers%20V1%20(text%20search).pdf

Dakazman

[EuropaTC]

Hmm. After the first caffeine injection of the day I wondered a bit more about this one.  I've got a copy of the book that Dakazman posted and according to that you need a 34mm choke for 400cc/cylinder with the caveat that you fit the smallest choke you can get away with. The TC @ 1558 = 389cc/cyl isn't too far away with 33mm chokes, or even with 32mm (350cc/cyl in the book).

31mm sounds too far away for the main jet of 120 but then again I'm only guessing and have very little experience with mixtures. Ideally you need an AFR meter plugging in to sort out these things from scratch.

If you want a quick shot without changing too much, I'd try a smaller main jet. I don't think I'd go to std Elan settings, that's for the 105bhp engine that first appeared in the '63 Elan and the Lotus Cortina. If you're expecting 120-125bhp then it's not going to be enough. Incidentally whilst looking through the Wilkins book before posting I note he says the Sprint/BV settings are good for 140bhp, so Ed Winter was definitely right when he said you didn't need to change for my VJ5 cams.

Finally, I know this is a fresh rebuild but one thing that I do find with Webers is that the accel. pump sticks if the car's left for a while. Sometimes only 1 out of 4, sometimes more. That makes the car very unhappy when accelerating, it's happened far too often when I lay up the Elan over winter so it might be worth checking that everything is moving as it should. (Dellortos have a different system and I've never had the same issue there)

Brian

[4129R]

Points, plugs, HT leads, distributor cap all new. I have tried two different distributors, no difference.

It feels like my Mini used to with the choke/cold start in the wrong position.

It run over after switching off which used to be a sign of too lean too hot.

I will check the plugs, screw in the mixture screws, and start from there, changing things gradually.

Does 22' advance on the strobe light at around 2500 revs seem right?

The Webers are 40DCOE151. The float levels were set at 15mm.

Having just checked the plugs, 1 & 2 cylinders look good, 3 & 4 cylinders look far too rich.

[4129R]

Problem solved. I should get Wally of the Week award for not spotting this earlier, but not even a Weber tuning specialist who spent about two hours trying to get the slow running working, spotted this.

He did however diagnose that the butterflies were not closing fully, told me to ease the two screws holding the butterfly, centralise them, then make sure that they do not stick when opening or closing, then screw them tight.

What he did not realise, which I find strange for a Weber specialist, is that the secondary venturis were not fitted to either 40DCOE.

I had the right 4.5 venturis with the screw fit, not the spring fit, amongst my collection of Weber parts, so after fitting them, the car ran perfectly.

Now I have to cure clutch slipping, gear selection very difficult, overheating, oil leak, slow running etc. etc, but at least I have a engine which runs sweetly.

[jbcollier]

Yes, leaving off major carb pieces can, only sometimes mind, be an issue ;-)

[EuropaTC]

 

Alex, I admire your quest for "Added Lightness" but think that's taking it a bit far......

[4129R]

Alex, I admire your quest for "Added Lightness" but think that's taking it a bit far......

Well, as you asked...... the radiator fan came off the spindle (new motor, smaller spindle with no flat part for the grub screw to fit up to), and sliced through the radiator.

Local radiator repair man wanted £255 including VAT to replace the core. Chinese aluminium radiator with new fan £130 including delivery from Czech Republic. Ally rad with plastic fan much lighter than original.

Only problem is the otter switch hole is M18 150 and the push in otter switch is 18.5mm. Nearest replacement is an M22 150 otter switch, so I have to use manual over-ride switch to turn the fan on.

People with these Chinese aluminium radiators must have solved this otter switch problem. Clues please. 

[SilverBeast]

I bought an adapter so a smaller switch would fit for mine,. Still haven't changed radiator yet though......

[4129R]

I bought an adapter so a smaller switch would fit for mine,. Still haven't changed radiator yet though......

1) Where did you get the adaptor please?

2) Where did you get the smaller otter switch please?

[SilverBeast]

Adapter: https://www.ebay.co.uk/itm/Female-to-Male-Thread-Reducing-Bush-Air-Water-Fuel-Gas-Pneumatic-adapter-Sump-/184636345653?_trksid=p2349624.m46890.l49286 and pick the one you want. You might want to fit an o-ring. My radiator had M18 thread ang the supplied bung had an o-ring.

Switch: (out of stock) https://www.ebay.co.uk/itm/Stoney-Racing-85-C-185-F-12V-Radiator-Fan-Switch-M14-x1-5-Temp-Thermal-/183540536941?_trksid=p2349624.m46890.l49286

I bought my radiator and bits in December 2019........

You should fit a relay to switch power to the fan, it'll be a lot less load on the switch and many can't deliver the current to power the fan like the otter switch can.