Emulsion tube quest - Page 2 (2025)

allencr267 wrote: ↑Fri Apr 19, 2024 10:47 amDoes the DCO have progression holes at the throttle blade, the DCOE has them under a brass cap, but a DCO pic has nothing there?
Blocking the last progression hole with a wood toothpick cured a too rich low end transition problem that a lotta new jets plus many with number drills & solder didn't come close to fixing.
IIRC emulsion tube pics & specs, the F11 is almost the only one that has any symmetry, an orderly pattern to it and that's why it works & is so popular across a range of engines. Hard to believe some could feed a consistent 14:1 ratio and engines could have such different requirements.

This is the same problem Holley 4500 Dominators have, the T-slot is too long. Also, several aftermarket sources of billet bases for 4150 carbs have slots too wide and too long. The people who market these carbs obviously never drive a vehicle with their product on it.

The excess fuel from the oversize transition slot (AKA "progression holes" in the Weber, Solex, Del Orto, etc. causes a rich condition that is untunable because if you fix one narrow range of throttle opening it messes up others, it can't be made right at all throttle positions.

Thanks a lot gents,

Yes it has the same progression holes as dcoe's

I have had the same idea, only to plug the first one.
When I cruise with very little opening it is very rich. But when I give just slightly more it leans out.

I will try the toothpick idea!

There is no problem in running 46 chokes.
The F7 tubes are way to rich.
You must get the idle jets right first to get the transition right.
I use the same carb and I use F9 idle jets between 55 and 65, I have to check.
How rich the emulsion tube runs during transition and part throttle is mostly decided by the tube cut out and the lower body thickness.
This is because during transition the fuel is high in the fuel well.
The right emulsion tube is the one that will passa enough fuel at WOT.
F9 is 8,2 mm in the lower body and will work up to a main yet around 175 or maximum 240hp.
Next is F15 that is 8mm and that will work fine for 240hp.
Above that use F2 that is 7,5mm.
So is F7 but F7 has a gigantic cut out and runs way rich in the idle system is right.
If your engine runs rich on top but OK at max torque use F3 tubes that have 4 extra holes that lean out when the fuel well height goes below them.
No need to alter anything in the carbs but check at idle how the throttle blades stand versus the progression holes.
They should be just before uncovering the first progression hole.
If it is open the idle screws get turned down to much.

Erland

I have seen this before and the solution was to use idle jets that were smaller than typical along with extra large air holes. These are not something that you buy however, and would require careful hand drilling. We ended up with an engine that would idle along in gear during rush hour, yet pull well to 7k. Don’t change your venturis.

The above post is the best advice I’ve seen so far, the F15 etube might be one to try. The pump jets/spring/bleed might be worth looking at to be sure they aren’t at any extreme settings at least. Can fine tune with those later if need be.

And it never hurts to recheck things like ignition along the way, is no fun spending weeks of tuning to find out there’s something wrong there, usually small but enough to make a difference…

Oh, and that’s good advice about the spring loaded needle/seat too, 4 cylinder engines can have some vicious vibrations.

Morning gents,

Thanks again for the load of replies!

I am using 55F9 idle jets any leaner and cruise around 110kph is affected too much.

I will check the progression holes and report back.

At least the car starts, runs and drives for now.

Following up on the vicious vibrations with four cylinders and side-draught carbs...

Not sure if you are already addressing this but in an earlier life I was a Renault fanatic and had/have references for support struts and rubber manifold joints etc. (ala Gordini).

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Sorry for my sluggish replies, I need to turn on notifications for this topic.

Thanks again for all the useful replies!

For me, till now, the biggest improvement on this subject was changing from F7 to F11 tubes.
So I am quite sure the issue can be found in the overlap from idle to main circuit.
Increasing the hole size on the idle circuit helps a bit, but must also control proper cruising around 100 to 120 kph since this is on the lean side already.

I am on board again, so coming 10 weeks I am not able to touch the car. But I will try all the suggested when I get back home.

My exhaust is huge, I welded a smaller pipe in it to reduce the noise, this also seems to have helped a bit.

zeemanstuning wrote: ↑Mon May 13, 2024 10:52 pmMy exhaust is huge, I welded a smaller pipe in it to reduce the noise, this also seems to have helped a bit.

Can you get at the collector to try a smaller collector or choke?