free hit
counters
Carb advice - Engine & Ancilliaries/Gearbox - The Lotus Forums Jump to content

Recommended Posts

I'll admit it. I'm dreadful at tuning carbs. Whether it's the Dellortos on my Eclat or the SU's on the MG, I just don't seem to be able to get the hang of it. I've read all the books, got all the gadgets but I still don't seem to be able to get a consistent smooth run. This is particularly pulling away at low revs. Once the Eclat reaches 2,500 it runs sweet, if rather noisy due to a hole in the exhaust. But a low revs I'm having to put my foot through the floor to get it to respond. Which sounds pretty awful at traffic lights! So, before I try to tune them again does anyone have any thoughts about this low rev lack of power? Too rich, too lean, accelerator jets? Anything? The carbs have been cleaned and completely rebuilt so that shouldn't be a problem. Help!

Share this post


Link to post
Share on other sites

Upgrade today to remove Google ads and support TLF.

Too lean, check your float levels. :thumbup:

Share this post


Link to post
Share on other sites

Is the ignition timing correct and if the distributor is fitted with a vacuum advance, is it working ?

Share this post


Link to post
Share on other sites

Timing is set at 9 degrees BTDC as per the book. There's no vacuum advance. Float levels are good. I will have another play with it at the weekend!

Share this post


Link to post
Share on other sites

Hello. I'd double check the butterfly valves are correct by looking through the progression holes. Make sure the throttle stop screw is only just touching the stop. Close all the air bleed screws. Close all mixture screws. Unscrew all mixture screws about 5 turns. Start the engine( might need a little turn on the throttle stop screw). Balance both air bleed screws on the front carb for the highest vacuum ( only 1 screw usually needs adjusting). Repeat on the rear carb. Then adjust the linkage screw to bring all 4 vacuums in line. If the revs rise to high whilst adjusting, drop the revs with the throttle stop screw. Hopefully you should have a nice smooth idle. Adjust the mixture using a colour tune or screw in 1mixture screw until the idle goes rough then unscrew 1turn. Repeat on other screws. If it's popping on overrun it's a sign of running to weak. Hope that helps a bit. Cheers J

Share this post


Link to post
Share on other sites

That helps more than a bit, thanks.  And at risk of sounding stupid can I confirm that the air bleed screws are the two on each side about halfway down the barrel?

Share this post


Link to post
Share on other sites

Yes the ones which are recessed. The other small screws half way down the barrel are the blanking plugs for the vacuum gauge connectors. The recessed screws near the manifold are for the mixture

Share this post


Link to post
Share on other sites

I've read this topic with interest as a tune up is the next thing on my list following the carb service kit service last year.

I set everything explained and it will make more sense when I look under the bonnet, but does any bright spark (excuse the pun) have a picture of their carbs where they can highlight the fuel and air mixture adjustment screws separately?

Share this post


Link to post
Share on other sites

This is the book to get, a good read.

How to Build & Power Tune Weber & Dellorto DCOE, DCO/SP & DHLA Carburettors Des Hammill

Share this post


Link to post
Share on other sites

I'm in the process of sorting out a couple of 40DCOE31 carbs picked up on ebay, using the (excellent) Des Hammill book mentioned above.  The only place it has let me down a bit is identifying what auxillary venturis are fitted.

 

The carbs take the spring type venturi, rather than the grubscrew ones, but I cannot find a number that corresponds to the sizes anywhere (the book suggests sizes start at 3.5).

 

What I have found is a small number moulded into the casting (not stamped) just below and to the right of the air/fuel inlet hole. I'm hoping this is not the identification number as I have two 1's, a 3 and a 4.  Mind you, it is perfectly possible given I've already found one 33mm and one 31 mm choke in one carb.

 

Any help on finding the numbers or, or tips on how I could measure them much appreciated.

Share this post


Link to post
Share on other sites

Pics and advice much appreciated.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×