Idle screw makes no difference

[MikeJ]

Hi

Trying to set up the carb mixture on turbo esprit using the des hamill book (and also doing carb balance using the carbtune). Curious problem is that turning in the idle screws on the rear carb makes no difference to the idle running. Turning in the screws of the front carb does make it go lumpy (but to be honest its not that smooth an idle anyway).

Progression is good and revs well.

Balance is good between the four chokes.

Timing is good and advances to spec.

Seems like its running rich based on the sooty exhaust pipe and sooty spark plugs.

Any thoughts?

cheers

Mike

Edited June 10, 2019 by MikeJ

[jonwat]

Get yo

11 hours ago, MikeJ said:

Seems like its running rich based on the sooty exhaust pipe and sooty spark plugs.

Any thoughts?

Get yourself a Colortune to set the mixture. 

[ekwan]

18 hours ago, jonwat said:

Get yo

Get yourself a Colortune to set the mixture. 

Not gonna help if turning the idle mixture screws don't make a difference.

[jonwat]

6 hours ago, ekwan said:

Not gonna help if turning the idle mixture screws don't make a difference.

By looking at how all the cylinders are running it'll give you a better idea of what's happening & you need it to set the mixtures accurately anyway.

[910Esprit]

On 10/06/2019 at 21:00, MikeJ said:

Any thoughts?

If progression is OK and you are running rich, the idle jet is not blocked and the progression drillings are fine.  I would therefore carefully check the single tiny idle drilling that exits directly under the closed butterfly, to make sure its not blocked.

Its not good practice, but you can probably poke a very fine piece of wire through it with the idle screw(s) removed.   You would also need to open the throttle, otherwise it may foul the butterfly 

 

Edited June 12, 2019 by 910Esprit

[MikeJ]

Thanks for the advice. Will give the colourtune a try as well

 

Mike

[910Esprit]

You may well be right and its not difficult to test.

My thinking is that we think we know that progression is good, which uses the same fuel circuit as idle.   I was looking for an issue that would affect idle but not progression.  

[ekwan]

On 11/06/2019 at 03:00, MikeJ said:

Turning in the screws of the front carb does make it go lumpy (but to be honest its not that smooth an idle anyway).

Progression is good and revs well.

 

Certainly sounds like you are running on progression & main. Does the throttle plate need to be open up in anyway for it to idle.

Seems like the idle circuit for the rears are blocked and not supplying fuel through the idle mixture screw.

[MikeJ]

I'm going to bite the bullet and strip & re-build them. It's been 12yrs since they were last done with a fair bit of sitting around over the winter.

[ekwan]

It may sound crazy. But after I refurbished my carburettors, I had to upsize my idle jets from 55's to 58's. Turning the idle mixture screws out beyond a certain point made no difference to the idle, at which point idle quality was still bad. Put simply, the jets weren't flowing sufficiently for proper idle.

[marode]

I may embarrass myself completely, but I once mixed up the mixture screws with the ones next to them after rebiulding the Webers of my Elan+2. Which had led to the same issue. Don´t know if such an idiotic mistake is doable with the dellortos - whis the Webers it was!