Running rich but I am afraid it is not jetting

J

Jamz

Member

Dec 14, 2005

36

0

• Dec 1, 2007

• #1

I have a 2000 YZ250 I have been trying to get jetted right. It is a fairly new topend, clean air filter, carb has been disasembled completly and cleaned, running 93 pump gas with 32:1 ratio(not adjusting oil to get jetting "right" and want to run oil richer for woods riding). The bike has allways run rich since I had it. I have been getting it closer with differnt pilot jets and even ordered a different needle to help. I have it where it runs great from 1/8 on. But idle to 1/8 throttle I can not get it cleaned up. It runs rough right to an 1/8 then just clears up instantly and will even pull the front wheel off the ground if you are not careful. I am about sea level temps in the 70's, humidity enough to drown you (Houston).

Right now I have it pilot #40, needle one clip down, don't remember main jet size but it shouldn't matter idle-1/8. I have tried a #38 pilot but it would get lean off of an 1/8. Air screw I have taken out 2.5 turns(which indicates a to large pilot) but still doesn't seem to be enough. Any idea's. It has the original reed valves but when I did a topend they looked fine...could worn reed valves cause this only at idle -1/8. I might pull the carb again and make sure the air passage is not plugged up.

Any ideas appreciated. I want to get it running smooth all the way from idle on and just can't get that last bit right!!!!

 

J

Jamz

Member

Dec 14, 2005

36

0

• Dec 1, 2007

• Thread starter
• #2

Other notes on the bike. I has an FMF Fatty and a FMF turbin core pipe on it. The original owner never had it jetting right(I know I rode with him). Top end was done with stock parts. Plug is a Br8eg.

 

F

Flux3D

Member

Aug 8, 2007

75

0

• Dec 1, 2007

• #3

I noticed you said that up to 1/8 throttle it runs badly. I am no expert on jetting but I do know that the air screw mainly controls this throttle range. In case you don't already know, try turning it out a little and see if it helps. I usually adjust my air screw every time I ride because it the easiest one to get to and it makes a big difference. Also, considering that it is humid where you ride, that would make the air less dense and therefore you need more air going to your engine. So once again turning the air screw out to lean out your bike should help with that too. Sorry if you already know all this but I figured I would post just incase.

 

J

Jamz

Member

Dec 14, 2005

36

0

• Dec 1, 2007

• Thread starter
• #4

I appreciate it. I tried that but it doesn't seem to clear it up. Turned it way out although it isn't supposed to make a difference after two turns and still nothing. :-( Called the local dealer and they recomended checking my reeds and presure testing the cases(which I don't know and probably don't have what I need to do that). :-(

 

Jaybird

Apprentice Goon

LIFETIME SPONSOR

Mar 16, 2001

6,449

0

Charlestown, IN

• Dec 1, 2007

• #5

Check here for an old link for a cheap, easy to make, leak down tester.
This 'pressure' test will let you know if you have a seal that is not holding, which means it can allow the tranny fluid to reach the combustion chamber.
Your symptoms might be indicative of a leaking seal.

 

sick 96 250

Damn Yankees

Member

Jul 16, 2004

1,207

0

• Dec 1, 2007

• #6

are you blowing smoke out a lot?

 

whenfoxforks-ruled

Old MX Racer

~SPONSOR~

Oct 19, 2006

8,129

2

Merrillville,Indiana

• Dec 1, 2007

• #7

What does your timing look like on the plug? Not a word about the reeds?

 

J

Jamz

Member

Dec 14, 2005

36

0

• Dec 2, 2007

• Thread starter
• #8

SIck 96 it does blow out a little smoke but isn't real bad. Not like it used to be.

Whenfoxforks-ruled.....I am not sure what you eman by timing on the plug. You mean coloring of the plug? I have not pulled the reeds to look at them. THey are old so I think I might just go ahead and replace them as it should not be hard. And hopefully that will fix it. ELse I will be presure testing the motor.

Jaybird....the link wasn't there.

 

Jaybird

Apprentice Goon

LIFETIME SPONSOR

Mar 16, 2001

6,449

0

Charlestown, IN

• Dec 2, 2007

• #9

try this:
http://www.dirtrider.net/forums3/showthread.php?t=87952

 

B

busted480

Member

Sep 27, 2007

10

0

• Dec 2, 2007

• #10

maybe you throttle slide is adjusted to high, not allowing your pilot to be used.

 

whenfoxforks-ruled

Old MX Racer

~SPONSOR~

Oct 19, 2006

8,129

2

Merrillville,Indiana

• Dec 3, 2007

• #11

The tip of the electrode. Does the side have any part that is as shiny as the top or dull and dark? Have you ever messed with the power, leak jet? The stock carb also shows a throttle position sensor.

 

W

WVFR

Member

Jan 4, 2007

8

0

• Dec 3, 2007

• #12

clean your carb.

 

2

2strokerfun

Member

May 19, 2006

1,500

1

• Dec 4, 2007

• #13

I've had to change the needle and the needle jet before to correct this problem. Normally, the needle wears more than the needle jet and you've already changed the needle...... I've also seen worn choke plungers, but that is rare and seems to affect the entire range of engine performance.

 

J

Jamz

Member

Dec 14, 2005

36

0

• Dec 12, 2007

• Thread starter
• #14

Everyone thanks for the responses. Sorry I have been tied up with finals, work and family. I have to take vacation just to breath. Anyways, I did replace the reed valves. They didn't look bad and seemed to have good spring back but thought what the heck. That really did seem to clear it up. I took the pilot up 2 sizes due to it was too lean then. Made sure the slide was seating down good. I did blow out the pilot port while I had the carb off and looked it over. I had torn it completly down and cleaned it just a while back and did drain it when it was not in use so all looked good. I think I just about have it right. It is running good enough for me to actually start doing plug chops to get the jetting dead on. Before it was so rich it just ran bad.

Once again thanks for the ideas and help.