Tuning detail

This is the about the last area requiring tuning. Marked in white dots. The image at the bottom of this post has red dots, these are showing the exact area of concern, this is just a couple of seconds of logging.

I gave the pump rods 4 turns of enrichment from where they were but have yet to test this, I didn't use the car today. The pump adjustment was related to another issue, not the one I will ramble about here.

Above shows a small issue.

This was climbing a gradual hill in 4th gear, the engine was not gaining rpm, as shown, actually just loosing rpm or just static speed. Torque is ok so I am not into the throttle too far. The MAP reading is not accurate, it is different to the reading in the ECU, it reads too high. I have two MAP sensors connected, the one connected to this software needs calibrating to match the ECU output. I don't need to do this atm. I will do this to finalise the ignition though I need to get logs on the MAP to work out the final load sites.

Anyway. I have pinpointed this area to a certain location on the throttle, rpm range.

It's when you should be accelerating (in the carbs mind) but you are not gaining rpm, lightish load, you are very gradually and slowly opening the throttle from a cruising or level situation, so the pumpjet is not active.

Basically I have a small gap between the idle/progression and main jet. This graph shows this perfectly on a creeping acceleration. This effects other areas but the effect is hard to see or less obvious.

So my current jetting is;

58idle jet
7850.9 idle holder (quite weak)
142 main jet
7 emulsion tube
155 air corrector

I need to very slightly enrich the 7850.9 idle holder at the top of it's range by filling in 1 of the 6 small air holes I think, I don't want a richer idle jet as the mix is good elsewhere and the airholes in the holder effect the top of the holders rpm range more than the bottom.

Also firstly test dropping the air corrector on the main jet stack to 150 and then use a 140 main jet. This will fire up the mains a tiny bit earlier using a smaller corrector, earlier in the throttle position/rpm.

I then hope that the high-end mix and the rest of the mixture on main jet stays as it was.

I will have dropped the main jet size and moved the main jet stack operation down slighly in the rpm range while taking the progression/idle upwards to meet it.

I will firstly test the 150 corrector using 140 and 142 main jet's and examine around 10mins of data on each rather than messing with the idle jet, as I have a nice setting on this...

Thats the great thing about logging this stuff, it's all there to examine, you just need to sit calmly and remember the drive and how the data relates to your feeling.

I know when I was taking this data shown in the image the engine was struggling when it got to 15.4AFR under load, this is fine at light cruise, but not when you are in a mild acceleration phase or bringing load onto the engine. Certainly 16.4 is way too lean.

I looked at the screen of the laptop at exactly this point cause the engine just started to hunt and faulter. I know it doesn't like 15:4+ under any real loading...

I had this happening just 3 times or so in two log sessions of 5mins each, but the underlying overlap issue is there all the time, just not enough to cause a faulter or hunt, just a touch marginal.

If I can sort this problem there will be a good torque increase in slow transitions in this rpm window, or this throttle position location, it's not related just to rpm but also TPS...It's a very small window like two-three hundred rpm and 5% on the throttle spindle opening.

If I just push the throttle a little harder the main jets come on as soon as the MAP reading hits 89 and the problem is gone I see this on a few logs, also the pump jet activates on firmer pedal usage.

The issue is on creeping slow throttle opening between 84 and 89MAP in the rpm range of 3000-3200 or so.

I know that on the 160 air corrector the main jet overlap on the same idle/idle holder is too late, this issue is present all the time, hense I am using a 155 :)

Using a 145 main and the 160 corrector, the main jet mixture once it's working is basically what I have on the 142-7-155, same all over, just a but late, so the 140-7-150 should keep the same mix and make it happen a tiny bit earlier!!

If not enough I will doctor the idle holders. I'd rather bring the main in earlier to be honest as it livens up the "drive", the active and eager main encourages you to gun the engine :)

Dropping the main jet size may not be bad thing if I can bring it in earlier as in some other areas I have a touch too much fuel just over this area I am trying to fix, the air corrector acts in two ways, effecting the start point of the main jet and the high end, the smaller corrector won't enrich the main jet much at lower rpm (where my issue is)....So maybe this is the "perfect" setting!?

So there is science to my suggestions.

You can see the same thing going on two blocks to the right of the dots, I just open the throttle the MAP goes up two-three points, a tiny bit, not enough to get any pump jet and AFR jumps from 13.6 which is ideal for the situation and hits 15.4, had I just opened the throttle a tiny bit more it would have stayed at 13.6 or enriched to 13.2 or so.

The area just before the red dots (to the left) is when I levelled the throttle to a cruise, the area in the reddots is when I just feathered it back on, so this area needs minor enrichment as I increase load. This not an area to use the pump jet really, too slow on the pedal, I have stiff pump springs to keep them quiet here!...I look at the pump jet as the last resort, this is a challenge for jetting!

This is really minor stuff now, just cleaning out the final few annoyancies.

I was delibrately feathering the TPS here to get this exact info!