idle jets

[C43]

Hi

I want to change the idle jets in the S3 turbo to see if it helps cure the hesitation around 3000rpm. Can anyone tell me if I just undo the two screws highlighted below and pull the access panel off to get to the idle screw holder? The Esprit setup is slightly different from that indicated in my book.

 

thanks

C43

[910Esprit]

Yes, that cover gives you access to mains and idles.   Idle holders are the slightly smaller screws with the O Ring.   19mm spanner to remove the air feed from the plenum.    

What size are you trying?

Edited October 13, 2017 by 910Esprit

[jonwat]

2 hours ago, C43 said:

I want to change the idle jets in the S3 turbo to see if it helps cure the hesitation around 3000rpm.

At 3000PM you're running on the main jets so changing the idle jets is going to have minimal effect if any. 

[C43]

its sort of 3000rpm and just below so I am going to give the idle jets a go. On the Dellorto bible it suggests idles will still have an effect but you are right I am on the high rpm side. 

I am guessing I have 40s in at the moment, I have 43, 46 and 50s to try. 

I had the car rolling roaded and they did a lot of work on the mains going much bigger. They got rid of a lot of the hesitation (it just would not pull through it), above 3000 the car really flies, its just below that I have an issue still.

worth a go I guess.

thanks for the feedback, I will let you guys know how I get on.

C43

[jonwat]

8 hours ago, C43 said:

I am guessing I have 40s in at the moment, I have 43, 46 and 50s to try. 

Don't forget to adjust the idle mixture screws in order to correct the emissions after each jet change. ☺

[C43]

thanks, I was not sure if I had to do this or not. I think it does say something in the Des Hammill book. Trouble is I don't really know what size they are now as I suspect they will be smaller than std due to the fuel residue on them.

C43

[910Esprit]

The difference between mine on 40s, or my preferred 43s, is almost exactly one full turn of the mixture screws from circa 3.5 to 2.5 turns to maintain a similar CO2.   I get no benefit from anything larger than a 43.    

Edited October 13, 2017 by 910Esprit

[ramjet]

Idle jets.

We want active jets, that's what we want.  

[C43]

20 hours ago, jonwat said:

Don't forget to adjust the idle mixture screws in order to correct the emissions after each jet change. ☺

 

20 hours ago, 910Esprit said:

The difference between mine on 40s, or my preferred 43s, is almost exactly one full turn of the mixture screws from circa 3.5 to 2.5 turns to maintain a similar CO2.   I get no benefit from anything larger than a 43.    

I fitted 43s today taking the 40s out. Unfortunately I don't have a CO2 analyser so had to guess the mixture screws. My idle actually rose when I screwed them out by 0.5 turns so I guess that points to them not being set correctly in the first place. I will have another go tomorrow. As for the hesitation well below 3k the car is sweet but between 3 and 4k it comes back. After 4k the car flys. Any ideas guys?

cheers

Christian

ps as stated elsewhere actually changing the idle jets is really easy.

[jonwat]

2 hours ago, C43 said:

Unfortunately I don't have a CO2 analyser so had to guess the mixture screws. 

Get yourself a Colourtune in order to set the idle mixture, without it or an exhaust gas analyser you're just geussing. ?

https://www.amazon.co.uk/Gunson-G4074-Colortune-Single-Plug/dp/B0012MB4VE/ref=sr_1_1?ie=UTF8&qid=1508013569&sr=8-1&keywords=color+tune

[C43]

ah yes colour tune, I forgot the joys of using one of those, I will give it a go thanks

C43

[Andyww]

I am a bit sceptical about the usefulness of a Colortune. I have one and used for the first time in years the other day but it only gives a very vague indication over the correct range. I ended up screwing out each jet until highest idle speed attained with each, then turning all 4 back in again one turn. The colortune was giving the same visible spark over this whole range. If it ends up too high reading for MOT I will ask him to turn them all in another turn until it is correct.

The only time the Colortune gave any different indication was when the screw was turned far too lean, but it was easy to tell by the big drop in idle speed anyway.

[C43]

ha ha thanks for your comment Andy. I played around last night with Colortune and thought I was going mad! Even at night is is very difficult to see the colour of the spark and even more difficult to see if I had set it right. The setting I arrived at were the same as just by doing it on idle speed as you say. I will have another go this week (I have a day off working on the Lotus booked!). 

BTW stupid question but screwing the idle mixture adjustment screw out (anti clockwise) is the right direction for richer?

thanks

C43

[Gis]

Yes, anti clockwise is richer

[jonwat]

7 hours ago, C43 said:

Even at night is is very difficult to see the colour of the spark and even more difficult to see if I had set it right.

Borrow the wife's makeup mirror, it makes it much easier to see the plug. ☺

[C43]

10 hours ago, jonwat said:

Borrow the wife's makeup mirror, it makes it much easier to see the plug. ☺

can't, she already broke it....

[Andyww]

Be careful with borrowing items for car usage, I have never been forgiven for borrowing her cake icing syringe for filling CV joints with grease. Cant see what the problem was at all, it was new grease therefore perfectly clean.

[Bibs]

I've got a turkey baster in the shed that'll never go back in the kitchen!  

[molemot]

The "idle jets" are poorly named...they also take care of the progression. Thus ...as I found... the build up of varnish from modern petrols, reducing the diameter, produces a hesitation misfire around 3000 rpm. I finally decided to check the ID of the jets using a piece of old guitar string, calibrated by my digital vernier caliper...and they proved to be significantly less than they should have been. I reamed them out using the guitar string and that cured the misfire. In the process of investigation, I discovered the progression holes in the carb venturis...these are covered by a brass plug and can get obstructed too, so they are worth a look.

[C43]

Right, having spent an afternoon tinkering I now have an esprit that pulls smoothly and strongly all the way through the rev range, what a joy. Its the first time I have driven the car with the engine setup correctly and it makes a massive difference. I think I had two problems, my idle jets were under size at 40 and also under acceleration the pipe from the airbox to the turbo was blowing off, leaning off the mixture massively (I have a bodged setup).

As far as idle jets are concerned I have ended up running 43s. I tried 46 but they gave no improvement so decided to go for the smaller size. The 43s removed the hesitations I was getting and improved the pickup from low revs. However the issue from 3000 to 3500 was due to the airbox pipe.

To setup the idle mixture screws I initially listened to the idle speed and adjusted each in turn to give maximum idle speed. I then tried using the Colortune kit and ended up putting about a turn on each screw leaner. To see down to the top of the plug I used an inspection camera which gave a very clear view of the color and made it easy to adjust the screw to get the bunsen blue. As a point of note the camera kept freezing. I think the EMF from the HT was interfering with the electronics. I wrapped the end of the camera with aluminium tape and that solved it. I bought the camera off ebay for about £30 and it has been massively useful over the years. 

thanks for the help

Christian

ps out of curiosity I will measure the 40s with guitar strings, any excuse to get the guitar out