Engine won’t rev up

[LozB]

Ok that's good

So what can cause the engine to run rich and blow a little black smoke on revving. We tried removing the air filter just in case that was blocked and upsetting the air fuel mix but still doing it.

Any other ideas? Could a stretched cam chain cause this?

[Carolyn]

Leaky injector is a possibility. You could pull the spark plugs and see if there's one a different colour to the rest?

Stretched cam chain is unlikely, but possible, especially if someone had tried to cure a leak at the chain tensioner by loosening just enough to get sealant in and bolting it back. That will cause a tight chain. However I' don't think it would make the engine run noticeably rich.