Exhaust gas problem on Lancia Beta 2.0 -DCNF 42- std.cams

[cheitane2003]

Hello Guy:
This afternoon I presented my car here in Spain for MOT.
I had a problem with gas.
CO 3,02%
CO2 5,04%
O2 10,9%


The problem is here:

HC 4404 ppm,,,,,the man said it sould be 200-400, but for such an old car 1000-1500 is admisible,,but never 4404.
Where can be the problem because CO and CO2 are correct.

Thank you very much.

[Guy Croft]

CO (carbon monoxide) is produced when gasoline is burned, the level is low so it says that the fuel that is actually being burned is burning well.

HC (hydrocarbon) is unburned fuel and the level is very high, an engine burning well on all its cylinders (even on carbs) can produce as low as 250ppm (parts per million) at idle depending on cams.

Here the HC level suggests that one cylinder is misfiring or not firing at all and throwing a large amount of HC into the exhaust pipe. This is not unusual to begin with when comp carbs are fitted!
This can be caused by a faulty plug (or HT lead), an ex valve not seating (pumping HC into the ex port on the compression stroke). Examine the plugs - one cylinder may have a fouled plug that is only firing intermittently - the cause can be incorrect setting on the idle mixture screw. If the mixture is too lean to burn the HC will go up as the fuel just pumps straight into the ex port, and if it's too rich the plug will foul up and result in the same thing.

There are other possible causes, chronic flooding due to faulty pump jets (dripping into the carb barrels) etc etc. My advice is do a compression test so you can rule out a valve problem, then get hold of a Colortune device (see links) and examine the flame while the engine is idling. I would like to hear what you find.

GC

[sumplug]

I had a similar problem with a twin cam running twin 45's. Turned out to be one of the butterfly plates was not closing properly due to partial seizure and a twisted spindle.
I would also check fuel pressure, as it maybe too high.

Andy.

[cheitane2003]

Hello Guy:
As you suggested I made a compression test and set the ignition with stroboscopic lamp, it was very overadvanced.
I found following compression values:

Cylinder 1 2 3 4
PSI 195 192 192 185


I used the colortune spark plug to set mixture and found the following numbers:


CO 0,301
CO2 7,01
HC 1588ppm
O2 10,62
COcor 0,618

This mixture was to poor,so opening the mixture screew half a turn all these changed to:


CO 3,629
CO2 6,80
HC 1866ppm
O2 8,25
COcor 5,220


In both cases I took out the breath hose tube from air cleaners to help HC.When you put a paper on the exhaust,sometimes it goes in, inducing an exhaust valve problem,but compression values are Ok.
Idle jet are 60, may be too big?But if I change them to 45 I found a big hole of power until 2.500 rpm.
Here I everybody say something different: valve play,wrong cam settings,valve seat,too rich mixture as the spark comes out very black.
But i don‚´t find a solution for this so high HC.I can play with CO in a waste region,but I always get a big HC.What do you suggest?

Thanks!

[Guy Croft]

OK, I'll try and help#

To commence please state:

- carb type and size
- choke size
- mains
- air correctors
- emulsion tubes
- idle we know - 45 -60 tried
- fuel pump type

Check your float levels (see GC book p119) and also the condition of the float needle valves. You should check to see if fuel is dripping into the barrels at idle from secondary venturi (main jet) or pumo jet, wear safety glasses.

GC

[cheitane2003]

Hello Guy:
The carbs are:
2 Weber DCNF 42
Choke 36
Main jet 145
Air corrector 185
Emulsion tubes F22
Idle 60
Pump jet 50 and in working order with new membranes.
Fuel pump Facet Solid State Pump with 4 psi pression.


I changed Idle jet to 45 and I got more exhaust explosions.After a while I got a stable idle with colortune.But I still have a big hole in the progression zone.After 3000 rpm the car pulls powerfull and clean.I didn‚´t go more than 4500 rpm because it has only 500 km.
And I‚´m completly sure that there is no fuel dripping into barrels at idle from anywhere because choke butterflies are dry.


I don‚´t use this part of the carburator because there isn‚´t enough place in the air cleaners for a good air flow,but I think this part has nothing to do here.Please,let me know if I‚´m wrong.

[Guy Croft]

Cannot see anything there that alarms me.

Possible ignition problem - misfiring periodically on one or more cylinders can do this.

GC

[sumplug]

Misaligned Butterflies or partially siezed ones. Fuel pressure incorrect.

Andy.

[cheitane2003]

Thank you very much for your help.
I try to find a solution.When I found it I‚´ll tell here.

[Guy Croft]

I am sorry I cannot be more definite.

All we have to go on is this: If an engine has very high HC and low CO it means that the fuel that it is burning - it is burning well, but unburned fuel is going into the tailpipe. This is usually caused by a misfiring cylinder.

GC

[G&G Motorsport]

Hello there,
Not so long ago I had a GC Twin Cam engine in a Lancia Monte carlo On My Dyno for carb jetting.
The set up was slightly diffrent to yours but for refrence here is the jetting we used.
175 Air
150 Main
40 pumps
I don't have to hand the tube numbers or the idel size( perhaps Guy can help)

Also in this case the chokes were small (34)

Perhaps if you have a problem with progression it is the mains/airs that are the problem ?

Hope this helps, if you can give me some more information I will try to help.


Phill

[cheitane2003]

Hello:
Following your indications, I opened the head in order to find what was wrong.It was the last solution.
And the problem was there: a bent admision valve in cylinder number 4 as you can see in the image.
But I achieved a compression of 185 lbs in that cylinder!
I will put the new gas tester numbers when I close the motor with the above fueling configuration.
Thank you to all for your help.
Siro,

[cheitane2003]

Hello Guy:
The last gas numbers are the following :
CO 1,46
HC 1670
O2 19,4

Do you know what can cause this so high O2?

Thank you very much.

[Guy Croft]

The oxygen goes up when it's burning leaner than stochiometric (14.5/1 A/F ratio) in other words it's too lean, it should be 2.8-3.5% CO at idle. The HC is high because it's not burning well, again, too lean.

Most likely the idle mixture screws need opening out.

GC