Hey guys,

I've been doing a lot of searching through the forum and there is a lot of good information. I have a stock 2002 ds with a K&N filter, modified endcap (homemade) with a 1.5" outlet, jetted with a 175 mikuni main, stock needle in the richest position. Elevation is about 1650 feet. Current gearing is 17/38. I am looking for an increase in power across the entire range without decreasing reliability of the engine, as I will be endurance racing it. I have a few questions.

1. What is the outlet size of a Mr Hp endcap for the stock muffler?
2. Has anyone tried to oval bore the stock carb? I have heard of people porting the top of the carb on a dirt bike to allow low end characteristics of a small carb with the flow qualities of a big carb?
3. Has anyone tried to port their stock carb in any other ways?
4. Has anyone tried to modify their carb the way the pro action does for two stroke carbs (putting a twist inside the outlet)?

I have read Oldmanracings posts on how to tune the stock carb and I am going to try them asap. I too like to tinker with the stock set up of a machine to maximize power. My next step is to port my intake myself but I am wondering if there is anything else that can be done with the stock system to get the power characteristics I am looking for.

 

No takers, how about just the outlet size of the end cap. The one I made is adjustable and I'm curious if going bigger or smaller would be better.

 

wish I could be more help to you, have you looked at any posts from Oldmanracing ? great source for info !!!

 

Most endcaps have 2 inch openings. A few at 2 1/8.
My son built his own out of billet aluminum 2 1/2 opening.
He calls it the Real Big Gun.
It extends out 2 1/2 inches from end of cannister.

There will be Stock Carb Mods II and III


Like your thinking, hope to cover all your thoughts.
Not much data on mikuni cv venturi mods.
Will have to experiment and probably destroy a carb.

 

Oldmanracing,

I built my endcap using a 3" stainless steel orifice plate. These are used in gas measurement and have precision cut openings in different sizes. I have plates with openings from 1" in increments of 1/8" to 2.25". I started with 1.5" and cut out the spouts on the stock end cap both internally and externally. I left the spark arrestor screen in place, but I may need to remove it to allow for a 2" diameter plate. The plate mounts directly to the back of the original end cap with two screws. I made this mod 6 months ago, at the time I had calculated that this would give me 2.88 times the flow of the original set up (area of a 1.5" opening vs 2 - 5/8" openings). A 2" diameter opening makes for over 5 times the original flow through the end cap! I've gained a huge amount of power over the stock set up already and was looking to try and increase the size in steps to see if more power was available. Looks like it's time to play!