Jetting on standard DATR/DAT type Carb

[Ferrit]

Seems you lot know more than a garage with a dyno and a AFR systems and a lot of my money!

Car runs really well and even on a short blast the plug colour is getting more like it, thanks again all and especially Capriblu :-)

before and after

[WestonE]

It makes me wonder if Hardings put the apprentice on the job un supervised. This is something I experienced at Emerald once leading to a hopeless ECU map with potentially terminal timing. It is so hard to find competent Carb tuning Dynos now and ECU tuners need to have plenty of experience alongside good kit. Beware 2X 30 somethings who setup last week or people who do not care about your car. Perhaps Northampton Motorsport or Aldon Automotive for trusted work based on decades of reputation. It does look like you are very close to having this finally sorted.     

[Ferrit]

Here we go after a trouble free 120 mile to and from Goodwood.  My sons had a driving lesson and there was a Alfa track day bonus going on

I drove down the A3 at 3000 rpm ish, and back roads had some fun on the way home.  I managed to shut my normally talkative son up with a couple blasts through the rev's and gears.  So what do you make of the plug colour on Champion N7Y's on the jetting recommended by Capriblu here

no2 (with the car in the background) and no4

Mark

[SanRemo78]

Bit of soot on the bottom of the plug but those electrodes look pretty healthy to me!

[Ferrit]

Drive it harder? ;-)

[capriblu]

So just a follow up regarding my expirementation with jetting - Having been able to get hold of previously unavailable sizes of jets I have finally settled on the following, which seems to provide smooth stumble free response, good econopmy and healthy looking plugs

Primary idle 0.7  (I did try a 0.65 but just not quite right)    (standard 0.5)
Secondary idle 0.9  (was on a 1.0 but having got hold of 0.9 this in combination with the above works well)  (standard 0.
Primary main  130 (unchanged from previous) with 165 air correction jet (was on a 160)    (standard 120 main/170 air corrector)
Secondary main 155 (unchanged from previous) with 230 air correction jet (was on a 225)    (standard 140 main / 240 air corrector)

One other thing that I have checked and adjusted was the opening/gap of the secondary throttle plate at closed throttle position. There was literally no gap (between throttle plate and body) so I adjusted this using the screw on the base of the carb to provide just over 002" gap.  Conflicting guidance on this "online" but general consensus that a very small gap (i.e. not enough to disrupt idle mixture/running) just helps towards minimisation of any momentary "fluff" as second throttle is opened.

Hoepfully with the above settings and good quality E5 fuel car will continue to run smoothly.

[Ferrit]

Interesting.  I will give this a go.

Your previous setting on my car ran lovely, no issues but was smelly, it smelt rich.  Even the 70 year old MOT man made a comment.  I was trying to understand what each jet does, so is this slightly leaner in places?

Re: opening/gap of the secondary throttle plate, I did try this on jet std jet setting and I quickly reversed.  I will try again.

Thanks as always to someone with more brain and time :-)

[capriblu]

Interesting.  I will give this a go.

Your previous setting on my car ran lovely, no issues but was smelly, it smelt rich.  Even the 70 year old MOT man made a comment.  I was trying to understand what each jet does, so is this slightly leaner in places?

Re: opening/gap of the secondary throttle plate, I did try this on jet std jet setting and I quickly reversed.  I will try again.

Thanks as always to someone with more brain and time :-)

The primary idle jet may have some influence on idle mixture but this should largely be offset by the necessary coorect idjustment of the idle mixture screw.  I would look at the following first ...


Float level - make sure not too high

Idle mixture screw - ensure correct adjustment. (close screw to point where tickover just starts to fall then screw back open slowly to a point just beyond position where tickover rises no further)

Secondary choke throttle plate. If this is set to give a gap between plate and body at closed throttle position then this MUST be very small, no more than 002"/003" otherwise will interfere with idle  setting making correct adjustment of idle impossible with rich rough running.


I checked CO at idle after first combination of larger jets and with a smooth tickover was able to get consistently just below 3%