Emulsion tube quest

[allencr267]

Does 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.

[Geoff2]

Another thing. I never liked the Weber spring loaded STEEL needle & seats. Carbs hanging off the side of an inline engine are subjected to vibration/movement. Not good for maintaining a stable fuel level. Redline in Hollywood, California sell Viton needle & seats for Webers. Might be worth getting some.

[Tuner]

Does 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.

[chimpvalet]

The source I posted for alternative E-tubes also is where one may find alternative slow run jets that offer broader control of that circuit.

[zeemanstuning]

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!

[Geoff2]

If you plug the progression hole above the t/blades, that will make it richer, not leaner.

[Erland Cox]

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

[Overlap]

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.

[zeemanstuning]

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.

[Kevin Johnson]

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).

[Geoff2]

Is the engine at cruise [ where it is rich ]......running on the idle cct...or main cct? That is why I suggested earlier in this thread to remove the Etube assemblies...& drive the car.
If you can reach your cruising rpm, then obviously the engine is cruising on the idle cct. If it is still rich, then your idle cct is causing the richness because with an air corrector jet that is 6-8 mm [ the threaded E tube holders ], there will be no fuel from the main system.
If it is lean at cruise, then the main system has started & you have a rich overlap. Bigger AC jets might be the answer.