Here is the old Mickey Dunlap top 10 list from the August 1996 Dirt Wheels magazine. Wouldn't you know it, I found it on my hard drive right after I finished retyping it? This is old so adjust the $$ over time.

HONDA 300EX MODS

This information was taken from the Dirt Wheels – August 1996 Magazine.

With a proven record for reliability, good handling and spunky though under stressed performance the Honda 300EX is enjoying phenomenal success. This electric start 282cc 4 stroke thumper has become a leader in the ranks of sport quads. Second in sales only to Yamaha’s BANSHEE, it has propelled itself into this vaunted position because it satisfies a wide range of needs inside a modest package. Can it be improved? Of course it can. It is under stressed engine-wise and it is relatively simple and inexpensive to extract more power and better performance from this vehicle. Here are 10 of the hottest tips that Four-Stroke Tech’s Mickey Dunlap has to offer for extracting the maximum in performance from this versatile off-road ATV.

PREPARE TO ROOST!!

1. I’d recommend installing a pipe first. The stock 300ex uses a very small diameter head pipe. We offer a 1.5 inch head pipe with megaphone exhaust that picks the power up considerably.

2. If you want to realize the full potential of any pipe mod on the 300ex then you need to install a black box mod with it. This will allow the engine to utilize the extra rpm that the pipe will give you.

3. You can get better airflow from the air box to carb by installing an intake tube from the old 350X. We have bought up quite a few of them and sell them for $45. The really do help overcome the restrictive stock 300ex carb air boots.

4. The stock carb (29mm Keihin) can certainly stand improvement. We have a 32mm carb kit we sell with throttle cable for $210. Combined with the pipe and black box mods you will see quite a bit of improvement in the EXs bottom-end, midrange and top-end performance.

5. After I had tried the pipe, black box, airbox and carb mods, I’d opt to install a higher reving cam for more midrange to top-end performance. Expect to pay from $120 and up for a reputable cam for the EX.

6. For more low-end torque I’d go with a higher compression piston kit. They sell for anywhere from $85 to $125 and are a good investment to make the Honda engine pick up power on the bottom-end.

7. My best power for the money would be a big-bore (330cc) kit for the Honda 300ex. We sell our 330 kit for $220 and it is a good value for the buck.

8. Once you start getting more power to the engine, you will need to do something about the increase in heat. We sell a low-priced oil cooler for the EX that lowers the temperature by 40 degrees for only $85.

9. Drill a 2-inch hole in the airbox lid, install a K&N filter and you will see a substantial gain in horsepower. On a stock motor we have found that we use about a #130 main jet at 1000 feet. A modified engine will generally run about a #140 main.

10. If you do modify the engine you will definitely need to add heavy-duty clutch springs to handle the load. We sell a heavy duty clutch kit for the EX for $17. You should also gear up a modified engine with a 14-tooth countershaft sprocket.

Hope this helps

CRR