![]() ![]() I use the dremel for everything from porting/polishing heads to boring carbs, works really well. I've used the same high speed cutter bits for 3 years now, they don't seem to wear out at all. I got mine at the local Ace hardware store, they have alot of dremel stuff to choose from, WalMart does also. The high speed cutter bits I mentioned are perfect for removing alot of material quick. Price out everything you need for the job, if you're only going to do a single head it might just be cheaper to buy one, a lot of members on here can set you up with a good head for a decent price. Best advice I can give then is don't try to enlarge the port at all, just try to round off all the sharp edges and roll the short side into the valve seat. Without a flow bench it's hard to verify if what you're doing is actually helping or hurting. If you don't have seat cutters then don't go near the valve seat, if you nick the seat then the valves are not gonna seal. All the right tools will cost a good chunk of change. ![]() You're also going to want a set of quality carbide burs in various shapes and sizes, and then some sanding rolls and mandrels in various sizes and grits. Im assuming harbor freight has a larger one, but I have no idea the quality and if it can stand up to the abuse. You're gonna want a more heavy duty one and one with a variable speed control. Then go in and clean things up with a little polishing work.The $9 one won't cut it, it will just stall out. I'm sure there are some shops out there that can get some more power out of the head, but unless you have some serious work already done to your motor, the best bang for your buck is a big bore kit. If you look at it in stock form I think you will find that there is not much more you can do with it. Plus I have never really thought about doing much with it. I honestly have no experience with porting a head designed like the Yamahas. Almost the same deal with the exhaust, except you will notice that the port is not channeled ( your choice in a exhaust pipe will decide how fast you can dump your exhaust here) and that there are two valves that are larger than the intake valves ( but are still lighter than one big valve and has the ability to flow just as well). Also this design helps the three small valves flow just like one huge one but with one more added benefit, you can rev to the moon because of less valve weight. This helps speed up the fuel mixture through the port or ports. If you look at the head you will realize that the intake port starts large and then splits down into smaller ports. This is one of the main reasons why yamaha went with a 5 valve design instead of a four or two valve. Even if you wanted to go bigger I think you do more wrong than good for this motor. ![]() Another thing to think about too is that a bigger valve will also add to your valve train weight, thus slowing down response and maximum RPM. Unfortunately I don't think you can just go out and buy bigger valves with out having them custom made. The only thing that I could think of that would make a serious difference would be to open the bowl around the valve. The idea behind porting would be to get a straighter shot through the ports into the combustion chamber and then out, but if you look at the 250f head the ports are already straight. Other than cleaning up the casting flaws, I don't really know what else could be done to the ports. ![]()
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