I get a fairly heavy deposit like this from my tailpipe (fitted with K&N 57i kit, Mongoose and RS*R manifold). The Mongoose tailpipe is fairly close to the bumper paintwork, with the result being I now have a heavy black deposit over the back bumper; it shows up particularly bad as the car is silver. The engine is not running rich; its always done this, and the garage reports nothing wrong with the emissions or the o2 sensor.

I've tried removing this soot only to find that it seems to have stained the paintwork. Use of a mild cutting paste (Halfords heavy duty colour restorer) doesn't seem to have had much luck in shifting it. Any suggestions?

Also, is there any way of reducing this sootiness, or do I have to live with it. (3/00)
You can buy some tape from demon tweeks - its silver in colour and it is designed to stick onto your bumper to protect it from this sooty stuff. I dunno if it works or if its any good. (3/00)
Yes I had seen this stuff. Would look a little cack if it started peeling off. Anyone know if anyone makes a proper alloy plate to fit to the rear bumper? (3/00)
You could try fitting one of those tasteful silver 'touring car' reflective silver stickers to your bumper above the zorst? Just a thought. (3/00)

Sooty deposits of your exhaust tip are indicative of your car needing tuning (paraphrasing the Haynes manual) - fair enough. My car has recently had its 63K service (on a 9K schedule) but funnily enough just 'cos Mr Mazda has had his grubby hands on my pride and joy doesn't give me the confidence that that means anything.

So what should I check - I was until last week running with high idle speed at start up following installation of a RB intake. I've adjusted the idle speed so it is again at 850 rpm. Anything else? (5/00)
A quick check of the miata archives (www.realbig.com/miata) indicates that black sooty deposits seem to be associated with cars running aftermarket intakes. I always got a fairly heavy sooty deposit with my car (with a K&N filtercharger kit). The garage said everything checked out ok; gases were fine, O2 sensor was up to spec.. It also looked from the deposits on the old exhaust that the car ran like this before it was imported from Japan. Normally indicative that the car is running rich? (5/00)