Fiat 1400 SOHC on twin Weber 40 DCOE: setting-up

[josko]

If someone knows the float level of this carb please tell me,
also I have a problem;

I fitted this carb in my 1400 sohc Fiat engine.

When accelerating it works fine till 5000rpm then stops accelerating and the sound changes, I checked ignition timing, synchronisation but I don't know what could be the problem so if someone has some advice for what to do please let me know.

Thanks!

P.S. I read the posts about carbs here ,and what to do before installation ,and I have done the most of sugestions, checked jetting, checked jets if blocked, checked pump jets and vacuum leaks.

[Guy Croft]

Hi, sorry I missed this post.

The 40 DCOE float cover should be held near vertical with the gasket, needle valve and float in place.

The distance from top of float to the gasket with the float hinge in light contact with the needle valve, measured with say a drill or round bar, should be:

Brass float: 8mm
Plastic float: 12mm

When fully open the distance should be 13.5mm

The choke may be too big, this can cause that noise, as can a cam profile of the wrong type, especially a regrind cam.

Report how you get on please.

GC

[josko]

Thanks very much for your answer, Guy.
Today I checked again vacum leaks on the manifold-carb and manifold-head connections and it is ok. My car doesn't hava enaugh space for the carbs so there is only 3,5cm from carbs to the car body.Sow I made a little experiment today and put piece of cardboard to reduce the intake of the air into carbs. Result was that the problem persisted but came on lower rpm. The plugs are black. I have ignition sistem with vacum advance and I can set the ignition by turning the distributor so what could be good ignition tu set for start?
Is it possible that there is not enoug air?
What would be good jetting for my engine?

[Guy Croft]

1", 2.5cm is the minimum distance permissible before the airflow into the carb is restricted, so yours is OK.

I just read another post that Dynodave answered regarding vacuum in which you said:

I have Fiat Uno with 1.4 SOHC engine with 32/34 TLDE carb and I bought 40 DCOE carbs with Alquati manifold. My ignition is driven by the Digiplex 2 and my question is how to connect vacuum to manifold to get same amount of vacuum as with standard manifold, because on std manifold all four cylinders suck the air from Digiplex 2 and on 40 DCOE only one cylinder has a vacuum port on the manifold.

Your ignition is timed from the crank front sensor, it reads rpm from the flywheel teeth. I assume this was standard from that engine no swapped?

This setup requires the electromagnetic sensor near the crank front pulley to be set opposite the lug on the crank front pulley at tdc, the timing is controlled by the ecu and you do not move the distributor to do the timing. If the Digiplex has been swapped from another model there could be some setting-up problems.

I need this info also from the engine setup to help further:
1. Chokes and jets
2. Camshaft type and timing
3. Exhaust manifold and silencers

GC

[josko]

Hy,
In another post I mentioned digiplex 2 because at that time I didn't know if it is ok but I bought an old type distributor that I mounted near the fuel pump and has pick up on it and ignition modul and vacum advance. Engine runs with it also and now I can set up an advance. Digiplex 2 system is standard from that engine, with flywheel senzor and distributor on the cam.

1. Chokes are 39-37mm mesured(on them written 45)-that I don't understand
air jet 200
main jet 125
emulsion tubes F9
idle jet 50
pump jets I think 50
2.camshaft is standard from this engine
cam lift: 8.8mm
valve timing
inlet: opens at 7degr.BTDC closes at 35degr.ABDC
exhaust: opens at 37degr.BBDC closes at 5degr. ATDC

(information from heynes manual for that engine type)

3.exhaust manifold is standard 4-2-1 and only one silencer at the end(don't know in english how to write this type of silencer-it is home made)

[Guy Croft]

For a start you need to set the timing at 10 deg at idle, 850 rpm without vacuum fitted to the distributor.

For the carbs on standard cam I reckon you want 32mm chokes, see item 22 at:

http://www.webcon.co.uk/weber/40dcoe.htm

Jetting F11 emulsion tube
115 main jet
210 air corrector.

That's my guess anyhow.

GC

[josko]

Now I see that I was wrong about the chokes. As I have seen on the link, I wrote dimensions of aux. venturis. Now I checked the right ones and dimensions are 27(item 22). Sorry about the mistake. Those carbs are new to me so please have patience.

Does it mean that I run to rich on the main circuit?


Thanks for the advices so far!

[josko]

Today I made a progress. As I have two sets of complete jetts (air, fuel and emulsion t.) of the same value I drilled a bigger hole on the air corectors to lean the mixture and engine runing improved a lot. Now my rpm goes to 6500 rpm till the overrichment problem ocures. I don't have another chokes to try so this was the only way to do something more.
I alslo set the ignition timing at 10degrees and float level properly.

I want to consult you on my next step:
where could I drill the holes on the emulsion tubes to lean the mixture more?Air corectors have no more efect I supose because of emulsion holes that are not big enough to suck that amount of air that air corector provide.

[josko]

New problem occured and I have no idea what could it be. When I increase the rpm and carbs start to work on the main circuit the fuel starts to dripp at only one barrel. The barrel on the needle side of carb.Also on the idle circuit likes to spit back hot or cold is the same. If someone has some explanation please tell me.

Thanks!


P.S. I got some jets and now I have
chockes 27
main jet 112
emulsion F9
air corrector 200

and the engine runs much better.

[Guy Croft]

Dripping fuel:

- Float level too high
- Fuel pressure too high (3.5 - 4.0 psi max at carb)
- Blocked pump jet bypass valve (in float chamber)

Spitting back:
- Bent valve (do compression test)
- Dirt in idle jet or idle fuel circuit
- Throttle plate out of alignment
- Idle mixture too lean (adjust by idle mixture screw)
- Flooding (see dripping fuel above)

You need to get a Colortune device to examine the flame pattern when running see:

http://gunson.co.uk/tools.aspx?cat=486

You also need to get service kits and strip overhaul the carbs completely, buy the Haynes Weber Carburettor manual and get to know your carbs.
I do NOT approve of drilling out jets or emulsion tubes and I have already told you the jets and chokes I recommend.

Do not post any more running problems until you have done the things I have identified above and all the things I have described earlier. Long distance fault-finding is impossible if the owner does not do what I tell him to do. This is a race engine website and people are expected to write that, yes, they are doing things thoroughly and professionally.
You will damage the engine if you continue 'guessing' like this.

GC