Jet sizes

[sandflyz]

I own a 03 CR 250 and my owners manual says there are two main jet needles for my bike. The manual lists them as a (6CHY12-82) that comes stock with the bike as it is jetted for sea level, and a -83 which is optional for a leaner needle. When i went to my local dealer, he gave me two completly differemt part #s for the jet needles. They were 6BHY38-74 which he said was the stock jet. and a -73. He said the leaner of the two was the -73 but he dien't know for sure. I'm assuming that the -74 is the equivelant to the -82 I listed above that was listed in my manual being the stock jet and so ordered the -73 to lean the bike out a bit.
Anyway finally to the questions. First. Why the different codes from the dealer to the manual, and did i buy the right jet, as i wanted the leaner of the two?

confused

 

[mtk]

I'll bet if you check the microfiche, there are a dozen different needles available from Honda. At least there are for my 2002.

 

[pw50123]

http://www.dirtrider.com/drtested/141_0302_pipe/ :nod:

 

[sandflyz]

I dropped the clip position on my bike from the second to the first and it runs great. The only thing is that where i live its quite cool this time of year. I'm going to buy a leaner needle for when it gets warmer as i usually ride in temps of between 16-25C. Right now its only around 10. I'm wondering what clip position to start with on a one size leaner neddle?

 

[NO HAND]

The needle you bought is not leaner, it is actually richer at 1/8 to 1/4 throttle. There is a lean spot on the stock jetting precisely at that throttle position and most people get the 6bhey38-70 to help that out.

 

[sandflyz]

Thanks No Hand. I finally figured that out last night, so this morning i went in and bought a -72. With the -73 the clip in the first position and a 400 main the bike runs great but does have a lean spot right where you say. My elevation here is 3600' and i usually ride in temps between 15-25C. Will the -72 help the lean condition from 1/8 to 1/4, or make it worse? With the -72 what clip position should i start with when i change needles?

 

[NO HAND]

I'm sure the 72 will help some, I had problems of detonation from 1/8 to 1/4 throttle so I was in a hurry to find the cure. If your bike runs fine, then there is no hurry, perhaps you won't notice the needle difference so much. I would say 2nd clip to start perhaps would be good. It's hard for me to figure out because I'm close to sea level and I have only tried, the 73, 71 and 70 needles. Lately, fuel quality is so bad here that I have to put some avgas into my mix. It's one cheap way to bring the octane up high enough to remove detonation.

 

[Sandy Whoops]

The 6CHY12-82 needle appears to be the standard needle for the 04-05 models. The 02 model's standard was a 6BEY30-74. I assume the 6BHY38-xx was standard for '03.

Only reason I jumped in was to point out that the 6CHY12-xx needles look pretty interesting. In 02 (and 03, I believe), we suffered from a lean problem at 1/4 throttle. Going to a smaller diameter needle was the only way to solve this. However, I believe that our 1/2 to 3/4 throttle suffers with these thinner needles.
The 6CHY12 needles have a slightly faster 1st taper. And perhaps more importantly, they have a shorter straight section. If Honda has the 6CHY series with a diameter around 2.740mm, I'll get a couple of them the next time I place an order and give a ride report.

Update: Further research shows different needles for the 04 and 05. Neither falls within an acceptable diameter for an 02 or 03. Only possibility I can see would be a drastic change in the size of the jet nozzle. Would be a fairly expensive endeavor to test a variety of needles and nozzles.