Been trying .5 main emulsions that start later than .7s. This means there's a lean gap where the idle circuit runs out about 3000 to 3500rpm.

 

So I'm trying richer idle holders. 

I have 7850.1 a the moment. These are 7850.3.

I'd prefer 7850.6 as there's so little difference from .1 according to the book I have.

 

I'd expect smaller top holes to make richer at top end of idle circuit delivery, but I'm not sure that's true.

Maybe inner diameter is different?

 

 

 

Edited 18 December, 20214 yr by dvderlm

For the holders worth fitting to sports engines, lean to rich 1,3,6,7,2,8 according to Eurocarb

• 7850.1       4 x 1.25        1 x 1.40
• 7850.3       4 x 1.30        1 x 1.40
• 7850.6       4 x 1.30        1 x 1.30
• 7850.7       4 x 1.30        6 x 0.55
• 7850.2       4 x 1.25        1 x 1.20
• 7850.8       4 x 1.40        4 x 0.50

Mostly Four top holes. One lower hole.

 

Edited 18 December, 20214 yr by dvderlm

I suppose I can JBWeld the lower hole and drill it with a 1.2mm or 1.3mm drill bit.

Dave Vizard explains emulsion tubes.

He holds them upside down so top end of revs matches top of the tube, which is too clever by half.

 

https://m.youtube.com/watch?v=1pkFSA_rRFI

 

Got around to trying these.

Had to reattach the choke cable to choke mech which I pulled too hard. It would not start without choke. 

 

Only swapped over the 44 idle tips. And moved nothing else to change mixture when I fit them.

Pretty sure they run leaner at low revs from what the AFR gauge shows. 

The holes furthest from jet are larger than .1's holes, so surely adding more air (and more fuel)

 

Maybe if I adjust idle richness up a tad...

 

 

Think I should swap back to the .1s in a semi-blind trial in case it is some other fault that has developed.

 

Now got some tiny drill bits in 0.1mm steps anyway.

According to this 

https://lotuselan.net/forums/viewtopic.php?t=40342&f=40&start=0#p281716

 

DHLA run idle circuit up to 3200rpm by design. 

So maybe the .7 main emulsions were a better choice to match the .1 idle holders.

Went to change back to 7850.1 idle holders and there might have been some emulsified oily stuff in the carb that feeds cylinders 3 and 4, at the edge of paper jet cover gasket. Mayo from dampness and air filter oil? But I think that's also the air feed holes for the starter circuit (basically unfiltered) which just has a fairly coarse plastic mesh cover. It wasn't crusty, no sign of blocked jets.

 

Added ~5ml of isopropyl alcohol directly into each carb to clean and mix with any phase separated water. Then started and ran it for a while, was idling smooth but around 16:1 AFR with the .3 idle holders. No stumble gently operating the choke flaps by hand.

 

Opened all 4 idle mixture screws about a 1/4 turn and this moved AFR to around 14.9 (but engine not fully warmed, so might be too much).

 

Need to check if doing that adds to the progression hole fed mix when drive on roads I know well in medium gear from 1000 to ~4000rpm at W.O.T with the .3 holders.

 

That's a bit better, but still tends to lean to over 17 at very light load 2200rpm.

So went back to the .7 tubes no change leaning at 2200rpm until I squirt accel pump, good at 3300rpm+.

So tried very rich .6 main tubes with .3 idle holders and good at 3100rpm+, but still leaning at light load.

 

I suspect there's a partial blockage in a progression circuit, or a sporadic ignition issue.

just think how accurate you could have it with a nice mpi set up 

Wide open throttle over 3800rpm it's insanely fast with .6 main emulsion tubes but then goes too rich and sounds a bit dull over 5800rpm. I saw 11.7:1 AFR uphill.

(would suit longer duration, higher lift cam )

 

Will blow thru the idle circuits at weekend. Wonder if a progression hole is partially blocked cause idle is fine, it's just low load 2200rpm that leans over 17. Pulled choke on a fraction to get back to mid 15s.

Found the .7 idle holders that were originally fitted to the Lotus Esprit Turbo these carbs came from.

 

On 2.0 (2.2?) litre turbo they use 40 idle jet with .7 holder (but 36 chokes).

Surely I don't need that much fuel on a little 1.3.

(I suppose the Turbo would have spun up and applied positive boost from 2500rpm on the Lotus blowthru carbs...)

 

Trying with the 44 idle jets. Turned in the mixture screws a tad...

 

 

Edited 7 January, 20224 yr by dvderlm

That's nearly sorted it, I had two periods of 17.8 then 18:1 AFR. One finished when I pushed gas pedal harder. Second stopped over a bump. I wonder if something is impeding an idle jet or two while moving, but drops away into the carb well when jets inspected. 

Or in the progression passage(s).

 

It's new behaviour since the change from .7 main emulsions. Why did I change it?

It was working.

 

Oh yeah, 99 petrol with up to 5% Ethanol is over £1.50 a litre. 

 

When I changed to .5 emulsion tube I lost a bolt that holds the jet cover and gasket down.

Clearance to the fuel pipe is awkward.

No matter, I replaced the bolt, but I've just discovered it is loose. I used an M3.5 cheesehead, but actually I reckon it should be M4. 

 

That would mean only one end of the gasket was held tightly down, so there could be a small vacuum leak.

Atmospheric pressure pushes down on the reservoir, but engine suction pulls fuel up the well.

For the main jets the top of air corrector is atmosphere,

but for the idle holders there's a rubber o-ring. If the o-ring was not sealing well perhaps that plus loose gasket would let false air in.  Not sure, need to see whether it will drive without a gasket.

Or whether correct bolt tightened down makes a difference. The jet cover gasket is just layered oil-proof paper.

 

On turbo cars it is rubber.

Too cold out there so I just swapped to an M4 bolt. That actually tightens down.

 

The removed M3.5 was touching the threads in the hole, so not completely loose as it would not just pull out, but not gripping.

And the bolt smelt of fuel, but should surely not be in contact with any.

 

On 07/01/2022 at 16:40, dvderlm said:

Found the .7 idle holders that were originally fitted to the Lotus Esprit Turbo these carbs came from.

 

On 2.0 (2.2?) litre turbo they use 40 idle jet with .7 holder (but 36 chokes).

Surely I don't need that much fuel on a little 1.3.

(I suppose the Turbo would have spun up and applied positive boost from 2500rpm on the Lotus blowthru carbs...)

Normally aspirated 2.2l  Esprits use 55 idle.

https://www.gglotus.org/ggtech/tesprit-dellortos/body-dellortos.htm

Jet cover gaskets tightened down and 44 idle with .7 idle holders is way better.

No 17.8:1 nonsense at high vacuum low load 2000rpm.

Using .7 main emulsions again as .6 was overdoing it.

 

Weather's not been so cold that I've felt the need to half block the rad.

But I have now also set the warm air feed to not supply any cold air, like I usually do in winter for better warm-up phase when the thermostat does open after 2 miles or so. 

 

Got some thick 2mm Flexoid gasket paper/card to cut my own new jet cover pieces. Just a rectangle with two 4mm holes. Should be easy.