40 DCOE carb on Volumex engine

[eski]

Hello Guy,

Recently I fitted a Volumex engine in my Montecarlo and I fitted a weber 40 DCOE carb but it doesn't run ok.
Engine is a standard VX with a CSC 4-2-1 exhaust. I used a pierburg electrical fuel pump and a filter with regulator.
Do you know the setup for this carburetor in a VX engine?

thank you,

Gerard

[Guy Croft]

Tell me what you have in the carb:

1. Choke size
2. Emulsion tube
3. Main jet
4. Air corrector
5. Idle jet
6. Pump jet

also tell the fuel pump type and the design of exhaust header and system/silencers

Photos of pump and exhaust always help,

G

[eski]

Hello,

Here i post some photos:
the exhaust sizes are :
35 x 4
44 x 2
56 x 1

The carb I'm using is a standard 40 DCOE.

Thanks,

Gerard,

[eski]

These are the specifications of the carb I'm using:
Choke: 28
Auxiliary venturi: 4.50
Main jet: 112
Idle jet: 50F11
Emulsion tube: F16
Air corrector jet: 210
Accelerator pump jet: 35
Accelerator pump back bleed: 60
Needle valve: 150

It was used on a Alfa Romeo 1300cc Gt Junior.

[Guy Croft]

Choke: 28 SHOULD BE OK
Auxiliary venturi: 4.50
Main jet: 112 TOO SMALL GO 145
Idle jet: 50F11 OK
Emulsion tube: F16 OK
Air corrector jet: 210 TOO BIG GO 185
Accelerator pump jet: 35 TOO SMALL GO 50
Accelerator pump back bleed: 60 OK
Needle valve: TOO SMALL I WOULD USE A 200/210

Fuel pressure at the carb with engine switched off needs to be 3.5-4 psi. Much more than that and it will flood.

If that doesn't help the problem may be the exhaust. Forget anything used on the standard VX because with its tiny carburettor they did not produce the kind of power a unit with a Weer 40DCOE will. The CSC 4-2-1 header you have is poorly matched to a supercharged unit and you really need a big-bore 4-1 manifold with pipe lengths 33-36". The pipe from the manifold needs to be 2" bore.

The silencing of supercharged engines MUST be big bore straight-thru which yours probably is not - resulting in high back-pressure. You many need two silencers of that type. Silencer boxes from turbocharged cars can be a good choice but I think - because of the noise - two similar to the type shown below would be best. If the unit is running well it should give a very characteristic & very harsh exhaust sound under hard throttle at around 3500-4000rpm which I would describe as 'tearing calico'.

I found a video which gives you the idea, yes I know it is a Lancia 037:

http://www.youtube.com/watch?v=x8NxVBzF9oc

You should publish a photo of the intake system so I can see the carb in place etc.

G

[eski]

Hello,

I changed the carburetor set up and the car it's very different, it runs so good.
For the silencer, do you think that a standard silencer from an integrale 8v should be ok?

Thank you,

Gerard,

[Guy Croft]

If it looks like mine inside..

You changed the carb jetting to the settings I gave? I am not sure please confirm, this is important because other people read these topics so we have to be precise.


G

[eski]

Hello,

Yes, I changed the carb jetting using the settings you said me.

Gerard,

[Guy Croft]

OK, great, thanks

G

[WhizzMan]

Now I'm curious. Is just one double barrel carburetor with 28 chokes not holding this engine back in peak performance? I would expect an engine with this sort of power output to have at least two double barrel carburetors with this choke size, probably even with 32 chokes in them. I have no experience with volumex setups, so it could be I'm overseeing something here.

[Guy Croft]

Fair question but it's the opposite of atmo fixed-choke carb tuning on a suck-thru supercharged. The more air the head flows the smaller the chokes need to be.

This unit may well work OK with 32mm chokes rather than 28s on 40 carbs but I would not rush out to buy & change them! I wanted to know the result on 28s first and it seems OK now.

If you make the carb and choke combo too big the engine won't pick up even off-load. Setting them up is really a question of experience..

G

[WhizzMan]

Fair question but it's the opposite of atmo fixed-choke carb tuning on a suck-thru supercharged. The more air the head flows the smaller the chokes need to be.

interesting and complicated material indeed. I didn't think about the much bigger pressure difference and "constant" velocity that the compressor would create.

[Guy Croft]

I should have added that that certainly refers to the VX blower.

Not entirely sure why but maybe the reverse flow thru the rotors upsets the fuel signal at the choke. I am not sure if it applies absolutely to helical screw units like the Eaton.

Anyone's welcome to comment on this.

Sorry to be a bit vague.

G

[LanciaNut69]

Hi Eski,

It's a fair project to fit a Vx engine in a Monte - did you leave the supercharger in its original position and alter the firewall, or did you alter the supercharger? What sort of ducting do you have to get cool air in because that is a big issue with this installation.

Looking at your pictures, I assume that you altered the right hand engine mount as you have retained the Beta driveshaft arrangement. You can use a Montecarlo diff output and retain the original driveshaft and engine mount.

If you have not already done so (difficult to see from the pictures) you will need to shield the right hand driveshaft cv boot or the exhaust will fry the contents in very short order.

I'd like to see some more pictures of your car and installation if you have them.

All the best

Darren

[eski]

Hello,

I used the montecarlo gearbox with the volumex engine.
I moved the volumex and I made two adaptors, one between the inlet manifold and the VX and another to fit the 40 DCOE carb.
Some photos of the car:
It's a gr4 replica.

Gerard,