Amazon: A bit rich

[JDW3696]

Hello all. My Amazon leaves its mark pretty much everywhere by way of black marks on the ground from the exhaust pipe. Photo attached. The tailpipe does point directly at the ground which doesn't help. The car is running perfectly but is this a sign it's too rich? Or just that it's the tailpipe being close to the ground. I'm getting about 200 miles from a tank. It's a b18 on twin su carbs.
Thanks
Joe

[powen1]

Joe, I thought you had it tuned on the rolling road ? should be ok
Is this black when it's cold ? i.e. choke or after a run ?
Did you get a compression test done ?

Paul

[JDW3696]

Hi Paul. Yeah it was all tuned and compression test done and all fine. Running well too. Im guessing it's just the proximity of the exhaust pointing down to the floor. These marks are left when hot and cold.

[Othen]

Originally Posted by JDW3696

Hello all. My Amazon leaves its mark pretty much everywhere by way of black marks on the ground from the exhaust pipe. Photo attached. The tailpipe does point directly at the ground which doesn't help. The car is running perfectly but is this a sign it's too rich? Or just that it's the tailpipe being close to the ground. I'm getting about 200 miles from a tank. It's a b18 on twin su carbs.
Thanks
Joe

I wouldn’t have thought that was much to worry about Joe.

Alan

[JDW3696]

Thank you. Was just wondering if it was the norm. I'll check the spark plugs and see how they look.

[142 Guy]

Manual choke?

Manual choke and precise fuel metering are contradictory terms. Assuming that residue is sooty (not oily) and that it occurs primarily on cold start up then it is likely a result of use of the choke. With digital fuel injection the ECU calculates the amount of cold start enrichment required based upon the coolant temperature and then continuously tapers the amount of enrichment and drops idle speed as the coolant temperature increases, checking the temperature every few micro seconds. The manual choke equivalent of this would require you to measure the engine temperature, precisely set the choke position based upon that temperature and then continuously adjust the choke position for the correct fuel mixture as the engine temperature increases. That is probably not happening. I suspect that most operators of manual choke vehicles apply full choke when cold and then push it all the way in when it will idle without help. Net result is that on cold start your fuel mix is probably running from slightly rich to grossly rich depending on engine temperature resulting in the soot. Given that the choke system on the carbs was designed to facilitate a start at -40C in Northern Sweden (or Canada), full choke probably results in grossly rich for most cold starts in the UK.

It is also possible that you could have an incredible accumulation of soot in the exhaust system from previous mal operation that is gradually getting 'rinsed out' by the condensation that forms on a cold start. This would gradually disappear.

If you are getting this soot accumulation following a hot restart or just sitting idling with an engine that has been up to operating temperature for a significant period of time then you may have a fuel mixture problem.

[Bob 1967]

It's quite normal, mine is always parked in the same spot and a Jackson Pollock is developing on the driveway.
It's only on start up, I usually pull the choke fully out and gradually let it in as tick over settles down.

[samaron]

My Amazon does the same thing. My assumption were exactly the same as 142 Guy wrote.

[Burdekin]

Setting the SUs up as described in the Volvo service manual results in them running rich at idle as well. So I would expect water and unburnt fuel when cold starting and idling.

[packers1712]

Originally Posted by JDW3696

Hello all. My Amazon leaves its mark pretty much everywhere by way of black marks on the ground from the exhaust pipe. Photo attached. The tailpipe does point directly at the ground which doesn't help. The car is running perfectly but is this a sign it's too rich? Or just that it's the tailpipe being close to the ground. I'm getting about 200 miles from a tank. It's a b18 on twin su carbs.
Thanks
Joe

I'm sure Neil has set it up properly, as many have already replied, I wouldn't worry about that black soot mark its not really an indication of the on the road condition.
I'm taking mine back this weekend for him to try some different needles as mine is running too rich at fast idle/cruising condition, so it is definitely something he considers when your car is on the rolling road!

Doug.