Two Stroke Motocross

Two Stroke Motocross Forum => General Two Stroke Talk => Topic started by: eprovenzano on August 19, 2019, 09:45:55 AM

Title: Jetting question on two stroke quad
Post by: eprovenzano on August 19, 2019, 09:45:55 AM
Not a MX question, but a two stroke jetting question on my quad

Ok guys... I've been fighting bad jetting on my 2000 Polaris Xplorer 400 since I got this machine. it on stock jetting... Yes it runs ok... but there are days want to set it on fire... It starts and idles perfectly every time (no choke needed, even when cold) without fail... so I'll agree the PJ is running slightly rich. Its the transition above idle that's killing me... at times it blubbers, coughs, chokes, but other times, it will get into the mid range (1/2 throttle) and then blubber... It will run in the mid range all day if you keep it below 1/2 throttle. You cannot get into a clean upper range. Sitting in neutral, you can open the throttle all the way, and it revs about 1/2 of where I think it should go. It doesn't completely rev out as a two stroke should, and it's worse with a load on the motor.

Changes I've made... I've leaned out the clip, 3rd to 2nd notch.. (3rd is where it was when I got the machine) runs better, but not good enough for me... If I move the clip to the top notch, the idle seems better, (could be my imagination) but then it will not rev out at all... pulled the MJ and found it's a 210. Cannot find a marking on the needle or PJ. I'm ok with the PJ for now...

I think I'm going to order jets larger than the current 210, (220 and 230). My semi educated guess as to what is happening... with the rich bottom end, its allowing the motor to get into the mid range, but the main jet is too small not allowing it to rev out... My fix is moving the clip to the top notch (leaning out the lower end), and swapping out the current 210 MJ for with a 220, or 230 to allow the carb to get more fuel and hopefully into the upper RPM range.

Title: Re: Jetting question on two stroke quad
Post by: eprovenzano on August 20, 2019, 07:44:38 AM
I'm starting to rethink the issue...  I'm going to pull the air box and see if more air changes the performance.  If it does, then the MJ is too large, and I need to go smaller...
Title: Re: Jetting question on two stroke quad
Post by: eprovenzano on August 20, 2019, 06:02:00 PM
I finally got the jetting right... YEA!!!!

I kept thinking about the jetting... when I got the quad the main seal was leaking, which i fixed. so it was always running rich. I thought before I order new jets, to do a test... I pulled off the air box and took it around the house... it was a little rich on the bottom, but open her up and holy cow she will move....  the air box is really restrictive.

Previously I had purchased a carb rebuild kit, it came with "stock" jets... I knew the main that came with the kit was smaller than the one in the carb (of course its not marked with a size, but based on a visual test it's smaller). I know I should only make one jetting change at a time, but I knew I was too rich and needed to address it...  So i pulled the carb, swapped MJ's and moved the clip up one notch... it now starts it’s soon as you touch the starter button.. and best of all it runs like scalded dog.. it's pretty fast for an old girl

I kept thinking it was too lean...  when all along it was too rich.  I think during it's lifetime, as the main seal began to leak, it was rejetted richer to accommodate the extra air.  Well those problems have been solved and it runs as it should...  I'll be on it this weekend, reopening some single track...  yes that is why I have it...  ;D  At least I bought a quad that's a 2 stroke