How to get the exhaust grime out of the jet pump housing?

[jetdrive]

I have a white bowl and place diverter. I am not sure if it is because they are powdercoated (I am sure the fact that they are white doesn't exactly help), but for some reason, it is just about impossible to get the exhaust grime cleaned off of them. The setback part of the pump which is painted is no problem.
I have tried simple green, mix of vinegar and water and even steam to no avail. Any other ideas?
Thanx in advance...
Mike...

[spectras only]

The bowls are usually powder coated ,so you can use silicone remover or acetone to clean the soot off.Or better ,check your engine temperature,if it's running too cold you have soot/grime problem.

[jetblue]

Try Whestleys bleache white, but make sure the pump is wet when you spray it on, rub it down good, then rinse. It is a tire cleaner, and is a little aggressive but seems to work. Be quick when you do it, so it wont etch or damage any coatings. This also works great on the scum line, if you get one.

[Jungle Boy]

I use Spray Nine cleaner. It works good for all the black soot that gets on the transom and pump.

[project-speed]

TSP.(trisodioum phosphate), It works on everything. You can find it in most boat shops.