Hi all
I posted this elsewhere but it was in more of a specific thread, whereas this is more of a general question.

Im trying to resolve high hydrocarbon levels in emissions and have read that its unburned fuel passing into the exhaust, usually due to misfire.

When plugs are inspected they are sooty which suggests its been running rich, could the sooty plugs be causing a misfire?

this is my theory so far:
1) mixture screws on the carbs were presumably too rich
2) this caused the plugs to go sooty..
3) which has an impact on the ignition
4) which probably causes misfires
5) which dumps unburned fuel into the exhaust, causing the very high HC readings on the emissions test.

is this on the right track or have i got the wrong end of the stick?
im hoping it'll be a case of turning the mixture screws on the carbs down and putting in clean plugs, and trying again.

just for ref, its a 2000 carbed R1, which has a catalytic converter on it.

Could be- I had the idle mixture on my ST1100 way too rich- it sooted up the plugs resulted in intermitent firing on one cylinder. Even when I corrected the idle mixture the firing problem persisted until I got new plugs.... (I was getting very high HCs but not too bad CO with a good compression test to suggest valves etc were okay)...

Other thoughts are- might an out-of-sync carb do the same thing? Might be worth using a carbtune to balance them (once the mixture is adjusted)...

I'd get the problem sorted- running too rich can knacker a cat.....

Just a thought, how many miles have you done in the car?

I guess lots of attempts at trying to start it in the garage, a few runs up and down the street at a maximum?

It may well be that there is un-burnt fuel in the exhaust can packing? If you try to start an engine several times the un-burnt fuel may end up in the exhaust system, which then drains into the packing material of the can. Most of it will evapourate, but it may leave some behind. Then when you get the CAT and the can hot during the test that un-burnt fuel vapourises and comes out the exhaust?

Just a theory?

Mike

I would go with guinness if this is the case. Try holding highish revs (perhaps 5000 on a bike engine) for 15-20 seconds to purge the exhaust, before carrying out the test.

The only way to really tell if the mixture is miles out is to clean all of the plugs and give the engine a good running at varying revs. Then check the plugs again. Either that or invest in a colourtune, priceless bits of kit

Usually high hydrocarbons are due to a misfire, but normally because the engine is running too lean, not too rich. High CO is a sign of running too rich.

Plugs will soot up even if the mixture is right if the engine is just sitting and idling, or being used on short runs and not getting up to temperature.

David

thanks for the info chaps. Yes the car hasn't seen the road yet so has been subjected to lots of starting from cold and just idling.
perhaps en route to sva it'll get hot enough to get the cat working properly.

Sounds like a colourtune might be a handy bit of kit! (quite tempted with the balancing thing too but its a bit steep!)
im going to stick new plugs in too while am at it, might as well reduce the list of potential culprits.

cheers!