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Engine Mods

Anyone that is going to be doing much serious mud riding with their Honda 300 is sooner or later going to be wanting to do some power mods to their engine. The 300 has got some power but once you get into aggresive tires over 25" and in some thick mud you'll soon realize that you need more to keep you going. These mods are in the order that I did them to my machine.

SuperTrapp IDS2

This was the first power mod I did. My stock exhuast finally rotted outover the years and when I went looking for a replacement I found a super deal on this one and just couldn't pass it up. this system is tuneable by adding or removing some of the internal discs to increae or reduce back pressure. I found this very handy when rejetting after installing the exhuast. I went from the stock 125 main jet to a 128 main and moved the clip on the needle to the second one fromt he bottom (pointed end). After this I found it to be running a little on the rich side so I add a couple more discs to make a total of 11 and that set it up perfect. I had the race core in the pipe for a while but it was just way too loud and would have been totaly usless during hunting season. Besides it also really pissed the neighbours off when I left early in the morning. if you plan on getting one make sure it's the Quiet Series and I'm sure you'll love it. After installing the IDS2 and rejetting I noticed a large gain in top end and quite a bit more bottom end aswell.


I added this to replace my stock one after I tore it. I had heard alot about the K&N and UNI filters and wasn't sure which one to get. I did a bit of talking with some friends that race MX about it. they used to all run K&N's but had switch to UNI's after one guy did and found that he was replaceing his rings half as much as when he was useing a K&N. they said there was slightly less flow with a UNI but it was more than stock. The extra engine life they got made up for the small flow difference. I also found out that to make the K&N as water proof as the UNI you needed to add an outwear that cut the flow down to the same as a UNI. With the cost of the K&N and outwear being over twice that of the UNI. along with what I was told by my race buddies it was an easy choice to make. You'll see the blueish purple colour in the filter. The UNI comes red. You have to oil it with a quality foam filter oil. I use Bel-Rays oil. It's blue and realy helps by teeling you what part of the filter is oiled and what isn't. You have to use foam filter oil and not Fiber Filter oil or motor oil. the foam filter oil is alot stickier to stay on the filter and to clean better. After installing the filter I had to increase my main jet to a 130 and left the needle in the same place. It was running slightly lean then so I removed 2 discs from my exhaust and it was right on for jetting. I didn't notice much more gain in top end but on the bottom end it was quite noticable.


Here's some thing that has save my ass a few times. It's not for everyone but it does have it's time and place. Clicking on HERE will take you to my snorkle page that will tell you all about building and jetting for one.

Port & Polish

This was acually the first power mod I did to my machine. If you follow any of my jetting instructions for any mods they might end up a little rich because of the porting and polishing I had done which would lean a machine out. This was not done by a professional and I do not recommend anyone to try this themselves unless they are totaly aware that they can really mess up there engine if they screw up or leave any loose metal inside by accident. I used to race 2 stroke bike years ago and at least had some idea as to what I was doing. Basicly all porting does is to remove extra metal in some of the corners of the ports to make them a little larger and straighter. The polishing just smooths out any of the rough flashing left from casting or from the porting. the result is greater and smoother flow of the intake mixture and exhaust gases. Which equals more power. It's acually not as simple as it sounds which is why I didn't recommend anyone try it themselves. I did this just shortly before installing my IDS2 exhaust. While at first I didn't notice a huge increase in power as I stalled other mods I seemed to gain more than what other I know had with the same mods. Right now I have enough power to turn 26x9.5 and 27x12 Vamps. With no piston or big bore kit. From what I've been told I shouldn't be able to. I've also been told that polishing and porting increases the power gains from other mods more son than just increaeing power itself. If that makes any sense but thats the way it seems for me aswell.

Piston and Cam

I haven't got these installed yet but as soon as I get settled in after moving these will be my next mods. I'll let you's know how they are in a month or so.


Basicly all I have to say here is that if you do any modifcations to your intake or exhuast systems to allow air or exhaust flow and you don't rejet to compinsate for it you are wasteing your time, power gains will be small if any. Plus running your enigne too lean can also cause high engine temps and premature engine failure.