Intake Manifold Carbon Build Up?

[olddog]

5.0 / 347 stroker engine.

Cam (from memory) is 236 / 242 duration @ 0.050" and 106 or 108 LSA

Mass Flow Injection system, which is a Edel Vic Jr single plane intake for a carb, with injector bungs welded at each intake port. A throttle body, designed to look like a carb, sits on top of the intake.

I had the intake off and polished it about 3-4K miles ago. I pulled the throttle body, over the week end (another story), and I was surprised to see the amount of carbon build up in the intake manifold. It pretty much looks like the inside of an exhaust manifold. I realize that with the valve overlap exhaust gasses get sucked up into the intake, however I wonder if this is typical.

With a carb there is fuel and air traveling in the intake at all times. Perhaps it washes itself out. In this case, the fuel is injected after the intake runners, so the intake runs dry, except for reversion flow at idle. It doesn't get much natural washing with fuel.

Do you see this with a carb or is this normal?

Also I was trying to decide what is the best way to clean it up. I'm not real big on washing a bunch of gritty carbon down on the intake valves. Advise is welcome please?