Hi

I have a 400 Scrambler 4x4 with a few mods on it, and want to know what Main Jet I should use, as well as what setting I should use on the needle.

I have a HPD Pipe, Pro Design Cool Head, Wiseco Piston, HPD Reed Spacer, Delta V Force 2 Reeds and RCR air box mods. I have just installed the airbox mods and reeds and spacer. Currently I am running a 270 MJ and a 6CEY6 needle in the middle position. Most of my riding is at sea level.

Anyone out there that has been here before?

ScrambledKiwi

 

Heres what I would do. 1st: Reeds & Spacer won't change your jets but the air box mods will. If your running a 270 w/ needle at middle. I would drop you needle down to the lowest setting and run a plug and mid throttle test(no full throttle), do this until you get your mid-throttle to clean running. Then up your main to a 300 or 310(K&N Power Kit will have these jet sizes). Run a plug test(and also listen for blubbering) and check for proper color. Do this until the color is light brown. Now if your in an area like I am, you will need to change these setting with the weather. Good Luck.

 

Thanks DS Lover.

What is Blubbering, and I thought you had to do the main jet first, then work your way down to the Needle, then PJ, then mixture screw in that order to get settings correct.

You don't think the 300MJ is a bit rich do you? Most of my running is at sea level.

 

Blubbering is the sound of a two stroke engine when it is in the transitional stage between acceleration and deceleration. You know the bapapapapa sound that you hear when you try and hold the throttle steady under a light load.

Personally I have never been able to make the sound go away. They all do it at a certain rpms based upon the porting and reeds. (The only time my snowmobile gets close to eliminating the noise is when the temperature is -20 Fahrenheit.)

Anyway 300 does sound a little rich doesn't it?

Looks like you have been reading the internet pages on how to tune a CV carb by starting with the main jet and working backwards. I read that article myself I would have to agree. It works out great on two stroke motorcycles.

http://www.factorypro.com/tech/carbtun.html

With a piped and modified two stroke I would be very careful of leaning out the midrange too much as this is where the vast majority of two stroke engine seizures happen. Proceed with caution in that area. Too bad you do not have an exhaust gas analyzer guage which would measure air to fuel ratios.

http://www.scuderiaciriani.com/rx7/AF_meter.html