Setting up carbs- from rebuild to running sweetly

[Rob Warren]

Hello Lotus fans.

 

I'm hoping you might be able to grant me some knowledge on getting my Esprit 1989 turbo running sweetly again. I've had the car since the start of the pandemic and only driven a handful of times. Bit by bit I'm working through its faults: replacing the alternator, wheel bearing, bushes etc. 

 

I noticed a strong whiff of fuel whilst driving and saw a big fuel leak when I was changing the oil. This lead me to believe that the carbs needed an overhaul as they hadn't been done in years, yet in hindsight I think the leak was coming from a perished fuel hose.

Anyhow, I've rebuilt the carbs with a kit from Southwest Lotus and Eurocarb fitted the  spindle bearings and checked everything. I've fitted a new throttle cable and now need to balance everything.

I've taken my guidance from the Dellorto and Webber tuning manual. The car now starts (3.5 turns out on the idle mixture screws). I've got a synchrometer tool ready to balance.

I've read a few posts on here regarding the colourtune tool. Is this worth getting?

So where do I start? Get the engine warm, get the idle set right on the main carb, get the second carb (airflow) balanced to the first. Other than the idle mixture screws and throttle idle screws, what else needs adjusting?

Any help greatly received. Based in Herefordshire. 

Excuses the gold in the engine bay. When I started the air box and turbo pipe were also gold! Also, excuse the amount of yellow!! Not my taste; I'll be working on this! 

Edited March 27, 2022 by Rob Warren
Missing text

[910Esprit]

The other key 'balancing' adjustment is the air bleed screws on each choke, these compensate for minor airflow differences between each choke, but make a big difference to idle quality.   I would personally use a device that can monitor all 4 chokes simultaneously,   such as a Morgan Carbtune.    The process is detailed in the service notes.   Maybe someone will scan you the page?  (I cant).   The order you have described above is not correct.

Fuel pressure and pump jet operation should  be checked too, but you can set your linkage/balance first.  3 1/2 turns sounds OK for initial setup.   I'm not a particular fan of Colourtune, although I do have one.   I prefer using my nose and looking at the sparkplugs!    

[Barrykearley]

Step up @johnpwalsh

 

[LOTUSMAN33]

Set the accelerator pumps with rig so all deliver 7.5ml with 20 pumps.

Close all the air bleed screws only nipping.

Close the mixture screws and open 3 to 3.5 turns

Make sure all the butterflies are shut then just touch the centre adjuster/carb joiner.

Wind in the idle screw so all butterflies just open.

Blank the vacuum off take on the inlet manifold.

Start the engine and set timing to 9-10 BTDC.

Get the car to idle as low as possible then adjust the mixture screw for best vacuum on all cylinders.

Reset idle so low as runs without stalling.

Now open the air bleed screw on the cylinder with the highest vacuum on each carb so it matches the weaker joining cylinder.

Now you can adjust the centre shaft joiner to level the carbs.

Adjust the idle.

Repeat the process again getting the best vacuum on each and repeating as this allows the carbs and engine to settle.

Remember only one air bleed screw should be open on each carb.

Run the car then check the plug condition so you aren’t running to rich, should be a nice tan brown colour.

If not and too black you are running over rich, a little black is fine as these engines run better a little rich.

 

As Steve says get a Morgan Carbtune, I, not a fan of the colour tune either.

 

Dave  

 

[jonwat]

You need the Colortune to correctly set the idle mixture & read this

[semi42]

But before all the above, 

check,  set ignition timing

check, set float valves

[910Esprit]

And finally, try to find a local MOT garage that are happy to work with you.   It can be a balancing act to get the emissions within limit on an older car - for you 3.5% CO2 I think.  If the car is otherwise tuned well, a small trick is to increase the idle speed until the CO2 falls with limit....   😉

[Rob Warren]

Thank you to everyone for a quick response.  I've purchased a morgan carbtune manometer.  and a new timing gun tonight.

 

If possible, I'd rather not take the carbs off again to check the accelerator pumps after replacing all the gaskets to the manifold and trumpets.  Is there another way to check?

Can I assume its best to time the distributor first (ease of access), then add the air box and turbo pipe before proceeding to use the manometer?

Thanks again.

 

Rob 

[910Esprit]

yes, set your timing before doing anything to the carbs.   NB set according to 'the book' which varies from model to model. 

Some folk reckon you can set the pump jets by the number of threads showing on the activator rods.  I guess it may be better than nothing, but it wont be accurate.   Only way is off the car using a test rig to measure how much fuel is pumped  (see Dave's version above above).    However, don't lose any sleep over it just yet, you can do all your other adjustments first and see how it runs. 

[drdoom]

Much good advice above with which I am in agreement. Yes, be certain first of ignition timing, valve clearances and overall sound state of affairs in the carbs. Watch out for issues with fuel pressure, particularly with a Turbo, as discussed elsewhere lately in TLF. Confident in these critical fundamentals then concentrate first on carbs balance at idle before looking at pump or other jets.

Cheers  

[Rob Warren]

Fantastic stuff. I'll update the progress 

[thebartman]

Just a side note - there are some Alfa sites that may have more info - as they also used Dellorto carbs (lots of people in EU/USA race these vehicles)  I'm sure Google can assist here ....   with my '85TE - getting the two carbs balanced first before anything else was attempted was a revelation. It took me about 4 attempts, as engine overheating became a concern whilst work was in progress. All this was done with a Morgan Carbtune - indispensible - as I got all 4 carbs balanced to within 1mm of each other. I had tried to skip this on prior attempts, and fixing popping/sluggish acceleration etc. all went away.

Good luck with yours  - it's a great feeling when it all works. 👍. 😃

[drdoom]

Yes, getting the carbs in balance is crucial and deficiency in that will show as popping on overrun, plus bad tip-in behaviour. Funny thing is that balancing can be more straightforward than many assume, and not in need of the assorted contraptions sold for the purpose. Quite simply, one can adjust out the subordinate carb whilst setting the master carb to just closed, then bring in adjustment of the slave to match by way of the connecting linkage. That gets one nearly there in one fell swoop. Balance is highly influential at idle therefore more easily perceived in running terms, and it is at idle where the synchronising gadgets ( notably Uni-Syn ) will foul up the proceedings due to airflow constriction.

Cheers

[DrieStone]

Good post, I'm getting close to needing to tune my carbs, and it's the only thing that worries me because there's so much black magic. I'm pretty sure I have a flow meter with 4 indicators and color tune somewhere 

[Steven162]

I really hope you replaced the accelerator pump diaphragms

[Rob Warren]

Yes I replaced absolutely everything - even the butterflies as they were bent.  Manometer and new timing light has arrived.  Just need to get some time on it now.

[ekwan]

Just make sure everything is air tight, especially the servo vacuum hoses