6 replies to this topic

[RichKay]

I bought a mini from Tokyo 1990 998cc with Weber DCOE carb, and stage 1 exhaust.  The problem I am having is there is wet carbon particulate coming from the exhaust.  I went to have it inspected and the HC and CO levels were really high.  I checked the jets in the carb and they were pretty clean.  The spark plugs are new but there is a ton of carbon on them.  I know there is unburned fuel but the only thing I can think of is that since the carb wasn't designed to be put on a 998cc engine, it is messing everything up.  The previous owner loved putting aftermarket racing parts on it even though it is a 1 liter engine.  I ordered a rebuilt SU and RC 40 exhaust hoping this will take are of my problems, it will take a while to get them from mini mania because I am stationed in Japan.  In the mean time I am trying to get it running a little better just to get it inspected and finish the title paperwork.  If anyone can give me some much needed advice I would really appreciate it.  The carbon coming from the exhaust is wet but it doesn't smell like fuel. I am not sure what to think really.

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[Vipernoir]

It's jetted wrong and running too rich would be my guess.

Either get it rolling-roaded by someone who knows Webers and stocks plenty of jets & tubes, or revert back to a standard SU setup.

[RichKay]

I was thinking it would be something to do with the jets.  I am eventually going back to the SU carb (1 1/2 Hif 38/4) and RC 40 when parts arrive.  It just really sucks there isn't much I can do to fix it enough to get by for a couple weeks.  I'm not going to drive it until I can get the carb put in.

[Ethel]

Hydrogen + carbon (petrol) bunrt with oxygen produces H20 & carbon. It's what's supposed to happen, but it may be running a bit rich if it's very sooty. The best indicator is to go for run to get it up to temperature and inspect the spark plugs afterwards.

[ArneBrys]

Hydrogen + carbon (petrol) bunrt with oxygen produces H20 & carbon. It's what's supposed to happen, but it may be running a bit rich if it's very sooty. The best indicator is to go for run to get it up to temperature and inspect the spark plugs afterwards.

 

This is not completely correct as perfect combustion of petrol (mostly C8H18) will give H2O and CO2 and not carbon. The richer it runs the less complete the combustion will be which will result in more CO (carbon monoxide) and pure carbon. A lot of pure carbon usually points to a rich running.

[69k1100]

True but too much oxygen usually puts holes in pistons or causes knocking. So when the context is a combustion engine and not a laboratory a proportion of the exhaust will be carbon monoxide and some carbon.

As you've already had the emissions checked there isn't much to talk about.
Just make sure your exhaust is properly sealed (and appropriately sized) other than that you're on the money with the webber. The chokes on the webber are massive compared to a stock su (1&1/4") I'd be surprised of returning it to stock didn't alleviate your problems. Probably lose a few hp in the upper rev range though.

[Ethel]

Carbon-carbon bonds are at lower energy than carbon oxygen bonds. That's why yellow flames (glowing soot particles) are colder, and also why you need to use the choke until you've warmed up the engine enough to create more carbon-oxygen bonds instead. Bonding oxygen to hydrogen releases yet more energy, so is essential for driving the carbon combustion, you just notice it more with a cold exhaust acting as a condenser.

 

As 69k says, excess oxygen is bad news as it'll combine with your aluminium pistons instead.