knocking noise when starting engine

[Deleted]

I have a strange noise when starting the engine, which totally disappears after a minute when the engine has warmed up and the choke is pushed in. Sometimes, when starting, particularly if I depress the accelerator too much, there is a louder bang and the engine stalls. At other times the knocking is quieter and fades away to nothing.

I have reconditioned the gearbox, and put two cylinder heads from a SD1 unleaded and reconditioned. I have a manual choke conversion, electronic ignition and electric Facet pump. These sounds existed before and after the improvements.

When driving there is no noise and the engine is sweet and powerful. I do, however, have a cloud of black smoke come from the exhaust when kicking down. Under normal driving the plugs colours indicate correct fuel/air mixture.

Richard Spratley thinks it is not the big/small end bearings but wonders about the starter motor not throwing out or locking in for too long.

Dennis.

[dorsetflyer]

If it is the starter motor jamming in then you could well have some damage to the flywheel and the teeth on the starter.
It's worth removing the starter motor to see if the bendix gear moves freely on the shaft.
The spring may be weak and the teeth on the gear damaged. If that's the case it's a replacement starter.
Check when the starter is out that there isn't any swarf in the bottom of the housing where the starter fits. If there is then the flywheel is being chewed up.
Clean up the shaft of the starter thoroughly in petrol or similar, and then spray the shaft lightly with some silicon spray, as this will make the shaft etc very slippery, and that may well be ok.
I know in days well past it was frowned upon to lubricate the shaft as it attracted dirt etc, but then silicon spray products were unavailable.
Finally of course the solenoid could be sticking on and would need freeing up.

[Phil Nottingham]

I would go for the starter motor - the black smoke indicates rich mixture are you using the correct dashpot oil? ie SAE 20 not engine oil. Does it do this everytime - I hope you are not in the habit of using Kickdown too often the BW35 is not really up it!

[dorsetflyer]

I agree the black smoke indicates a rich mixture. Remember when you floor the accelerator to get the sudden change in power the engine will need more petrol than air, so it stands to reason there will be a slight imbalance momentarily which will cause a puff of black smoke.
It will only hurt your wallet.