Emulsion tube quest

[zeemanstuning]

Hi gents,

New here and having a difficult question

I have a 3 liter 4 cilinder Volvo stroker b230.
Ported head 46/38 valves.
Rough cam 300 dur 14.d lift lca 105

I use dco 50sp's

The car pulls and runs great. 210whp and great torque.

But anything below 2000 rpm cruise it runs pig rich.
I went from F7 to F11 tubes this made it much more driveable already. Butt still stumbles rich on low rpm cruise.

Chokes are big 46mm
Main 180 air 160 idle 55f9
Carbs act small which is weird for such sized carbs.
But probably the pulse of the stroker engine is great at such rpm.

I am using F11 tubes now, any idea what to try next?

[Geoff2]

Have you tried bigger air correctors 180-200?
With the bigger AC jets, try the F7 E tubes.

Or F16 E tubes.

[Geoff2]

Have you tried bigger air correctors 180-200?
With the bigger AC jets, try the F7 E tubes.

Or F16 E tubes.

[BLSTIC]

I'm not that up on carb calibration, but I've head of low-mid rpm rich being caused by reversion (but that was at WOT). If it *is* reversion, you'll probably find it hard to calibrate out. Header or cam timing changes might be in order if it's otherwise uncurable.

[mag2555]

If your intake valves have a back cut done to them and or there chamber side face have a radius on them then as a last resort try out ones that do not.

[Geoff2]

Another combo you can try: smaller main jets, maybe 160 or 165 with 140 or smaller AC jets.

[Lshungy]

Weber fuel circuits vary rarely over lap un like holleys etc . So if you’ve tried playing around with idle circuits etc( I’m guessing you have small throttle openings at those revs ) or float heights ( very important) I’d be looking at reversion . Webers are also very sensitive to air cleaners and in particular trumpet lengths .
Cheers Carl

[Chris_Hamilton]

Delete

[chimpvalet]

Try these, they have been a resounding success. Developed through years of analytical work by a dedicated technician/enthusiast.

https://www.webstore.com/item/VP-Main-C ... /116292961

Cheers

In your specific case the better choice likely would be the VP tubes for large choke settings, also via the same vendor.

[Chris_Hamilton]

IMO just changing the emulsion tube isn't going to solve your issues. Going from the richest (in terms of DCOE/DCO) emulsion tube to the leanest makes no sense to me. Your chokes are way too large, you would be better off with a 42 or 44 mm choke. 42 would be much better if you use it on the street. 46mm chokes are one of the main problems IMO. The idle jets are too small, especially relative to the main jet size. I would bet that your accelerator pump jets are off as well. With that big of cam I can't see the emulsion tube coming into play at 2K rpm. More like 3500. Personally if it was me, I would start over from the beginning, verify proper idle and off idle operation, tune for WOT with your main jet, etc. etc. There are several good manuals covering tuning DCO/DCOE's might be a good investment.

[Tuner]

"But anything below 2000 rpm cruise it runs pig rich."

Fuel pressure/Float level too high?

[zeemanstuning]

Morning gents,

Thanks a lot for all the replies! Much appreciated.

So I will try to answer all.
I saw a post about F16 tubes, I ordered them, will try.

About changing air correctors etc, I did both together with main jet from 160 main till 100 air corr.
I had larger idle jets as well like 65F8.
But all doesn't matter.
Ofcourse it matters a bit but nothing very much.

I have had 48 weber on the first try with much milder cams. But also with the 48webers and 42mm chokes I had the same issues. Even with the smallest idle jets.

I do have all the weber documentation, and the problem is recurring thing, no matter the cams or the carbs.
It looks like being caused by the large stroke of the engine.

Reducing choke size will only give better signal and make things worse. I am trying to buy 44mm chokes but not much luck till now.
If chokes are too big all would be lean because of lacking signal, not rich. Dyno guy told me choke size is good.
There is not many of these engines doing 250hp normally aspirated

I am sorry for not telling the whole history of the story.

Yesterday I put in 35 instead of 45 pump jets and it didn't do much.

Can anyone confirm that F16 tubes are leaner in the bottom than F11?

Erland suggests to use F2 or F3 tubes. Need to order that too.

The guy who was doing the tuning on the dyno is 73 years old and doing carbs all his life. We tried a lot of things but this was the best setup till now. Smaller idle jets give a lean blib when trying to drive away. And still not solving the rich issues around 2000rpm

About the float hight, fuel pressure etc, I have been trying endless things with that too. But seems OK now. Also at idle.

I am really quite sure that main circuit starts too early and needs another emulsion tube. Only need to figure which one.

In the carbs calculator it says that because of the large displacement I need a size 6 aux venturi to start the main circuit a bit later. But there are no such aux venturi's.
All these things tell me that main circuit starts to early

[Geoff2]

[1] One or two carbs on the engine?

[2] Agree with others that chokes are too big. Big-ger choke does NOT automatically translate to more HP.

[3] With such big carbs, only small throttle opening required for cruising. Are you cruising on the idle cct or main cct? Try this: remove the m/jet, E tube & A/C assemblies. Test drive at cruise. If you can reach your cruise affected rpm, it means the idle/progression cct is rich &/or the main system is coming in too early & you are getting a rich overlap. A bigger A/C jet could be tried to fix that.

[Chris_Hamilton]

Have you verified (with gauge while driving or dyno) fuel pressure is no more than 3.5 to absolute max of 4 psi? Could be as simple as that.

[zeemanstuning]

1. Two carbs
2. Yes agree that chokes could be a bit smaller, but it drives well and responds well. So yes I will try smaller chokes, but as above I have tried smaller carbs and chokes and cams but all had the same issues. Only thing that made improvement was from F7 to F11 emulsion tubes. And I tried yesterday on the highway from 3/4 to full and 1/2 to full etc. All makes a difference it pulls really the strongest on the full opening. So that also tells me that it handles the carbs well.
3. Thanks will try and get back here
4. I have a proper fuel pressure regulator and a gauge. Pressure is adjusted to 3psi. I have tried higher and lower pressures, smaller and larger needle valves but no improvement or worsening