N E 1 ever port & polish their intake down tube from the
carb to the head on their own? If so, what should I look out for?
Should I even attempt it? The down tube is cast aluminium and
looks jagged as hell in there ....

If there is alot of flashing left from the casting process, that's ok to remove. The rough cast edges are actually beneficial though. It swirls and disturbs the air on the way into the cylinder, creating a mist of fuel/air that combusts better. Polishing the intake will cause the fuel to condense on the intake wall and it won't burn as well. It does make the air travel faster into the head but the mix won't burn as well.

Fireballsocal couldn't have a better job at explaining this.
Don't remove the rough surfaces. You will regret it.

Instead, if you already removed the cylinder, you can smooth out the the ports on the bottom of the cylinder and get a slight better performance.

The more I learn about this, the more I realize I shouldn't screw with it myself. =)

So, don't port & polish it ?

Porting and polishing the head is completely different from the intake tube. Leave the intake alone. If you are after extra power and wanna spend the money, send your head to a reputable shop to port and polish it. This will maximize the efficiency of your valves. Flow bench testing is very beneficial in this mod and I would recommend anyone who messes with your head to flow test it also.

Porting is when you change the shape of your intake and rough up the surface. The rough surface doesnt affect the air so much as it does the fuel. Think of it like this: Put water on a glass surface such as a table. If you blow the water, it just runs along the smooth surface. Now, put some water on a concrete surface or sand paper, if you blow the water, it "jumps" off the surface into the air. That is what's happening in your intake when you port it. The fuel hits the rough surfaces and atomizes and mixes with the air much better.

um what bike and engine are we talking about?

i thought they use mirror like polishing on 2 stroke exhuast ports. air and gas dont need to be mixed when its already been burnt. just wants to get the hell out as quick as possible.

I do my own, or should say starting to. So far between me and a buddy experiementing we have done a few cylinders with positive results everytime. Last two we did are my CR500's, the 89 needed a boost but the 84...can't wait to ride that one....that was the only mod left to do...lol.

But yes you can do it yourself, polishing is actually only done on the exhaust....help the bad get out faster. If you don't have a general idea of how it works I would not try without getting some more insite. If you think you can do it, it will save you a hefty machine shop bill but it could also cost the price of a new cylinder...kinda a crap shot....guess that don't help.

thats what i thought.