2003 CR250 Tuning Help Needed

[bigbad29b]

I have a 03 CR 250 and have been trying to solve a bogging issue. The bike always fires right up. Never a problem cranking. I'm wondering if it's running too rich. Here's the issue. I can fire it up and it will always need to be rev'd "hard" to clear it out then I can take off with tons of crisp power from low rpm to wide open. After clearing it out, I can take it easy riding around the trails for a couple of minutes and then I get on it trying to wind it out, I get the bog again and have to clear it out again. If the bike has been sitting a for a while, I crank it, let warm up for a few minutes, I can jump on it and i get the bog until I rev the piss out of it or get on a long straight away where I can wind it out. The bottom line is I have to be in a riding situation where I can constantly get on it or I'll get back to the lower end bog.


The topend has been rebuilt and the exhaust valve was removed and cleaned. I also checked the servo for opening and closing the exhaust valve. When I bought the bike it had had a Pro Circuit pipe, FMF Shorty, and VForce Reeds.

I recently ordered a JD kit.

What I have tried:
-I tried different size jets
-I checked the float level
-Tried a new spark plug
-Cleaned carb and air filter

Tried since ordering the JD Kit:
-400 Jet (JD Kit)
-White needle 3rd slot from top (JD kit)

Tonight I have pulled the needle and moved the clip to the second slot from the top of the needle. I will be taking it out this weekend to do some testing.

Are there any ideas from anyone that I can try this weekend?

Any advice would be great. I have never owned one that required this, so i'm wondering if there's a larger issue.

I will say this, when it's cleared out, it will scream. Tons of crisp power.

Thanks,
Brad

 

[arnego2]

Ok where is your jetting now, needle setting, pilot?

 

[bigbad29b]

Last weekend:
JDkit main - 400
JDkit pilot - 32.5 I think
JDkit white needle with the clip in the middle slot(3rd from the top)

Now it's set for this:
JDkit main - 400
JDkit pilot - 32.5 I think
I just moved the clip on the needle(JDkit white) to second slot from the top

I haven't fired it up since I moved the clip.

Thanks!

 

[High Lord Gomer]

Is it a classic lean bog where you twist the throttle and it just dies or is it more of a stumble and stutter where it doesn't seem to fire consistently? It sounds like the latter and I think you are right that it is a rich condition. Moving that clip should make a significant difference.

 

[bigbad29b]

Seems rich to me. Sitting still while twisting the throttling will eventually clear it out. Or in an open area where I can wind it out it will clear out. Never seems to be be starving for fuel. Seems like too much fuel. I've never tried moving the clip so hopefully this will make a difference. Thanks.

 

[High Lord Gomer]

It would also be worth checking the float height next time you are in there.

 

[bigbad29b]

It's 15 mm

 

[CR3999]

What range of the throttle is it bogging in? If it is down low it may be as simple as the air screw. Mid-range we be the needle or clip position, at top is the main.

 

[bigbad29b]

It starts low to mid-range and continues to the top until cleared out. I get on it a few times and it will clear out. Then you can get back to some tight trails where you can't open it up and it starts again. I need to wind it out to clear it out again.
Thanks for the responses.

 

[arnego2]

How do you ride? It sounds like the carb just loads up because of lugging around.

 

[BSWIFT]

How many turns "out" is your air screw? The starting point should be around 1 1/2 out. Very important to only make one change at a time when tuning the carb. Follow "Spanky's guide" at the top of this forum and you will get it right. Tune from good idle to the mid, and then the top end. BTW, it sounds rich to me as well.

 

[bigbad29b]

arnego2 - I ride mainly trails, but I get this behavior on trails, tracks, etc. The trails we ride on are north of Atlanta @ Moto Mountain or West of Atlanta @ Highland Park. Each place has areas of long open trails where you can open it up good. There are other areas of more narrow tighter trails where the speeds are slower. I agree with the loading up.

BSWIFT - The air screw is 1.5 turns out. I'll check the guide out as well.

Thanks to all. I'll be taking it out Sunday to try the clip move of the needle and plan to double check the air screw, float level, etc before sunday. Ill let you know what I find.

 

[arnego2]

It is pretty difficult to jet your engine correctly if you have very different areas to jet for. If you run the bike for dessert you have to rejet if you ride in tight trails. If its only sometimes you could use the airscrew turing it out half a turn more if in tight areas. A little lean on the pilot circuit will not melt your piston except you running the iddle for half an hour :)

 

[bigbad29b]

All good information. I'll let you know how it goes this weekend.

Thanks again

 

[bigbad29b]

Went riding sunday. The JD kit white needle with the clip on the second slot from the top seemed to be the best. I moved the clip to various slots and was able to see the richness and leanness changing. Don't get me wrong, it did seem better down 1/4 to mid throttle, but I did still have some of the same bogging. Not as bad. I tried adjusting the air screw too. I'm still not thrilled with this but it's better. Now to throw an idea into the mix. I have a new PWK carb sitting around. I've seen lots of discussions around this switch, but haven't tried it yet.

 

[arnego2]

On jetting you need to start at one point, best would be idle, pilot and airscrew, then mid range, last main. click here is a good read.

the carb is not exact, meaning your pilot range mixes with the needle and the main interferes with the needle range too. I tried a lot of different needles and ended up with a JD kit. On another bike, same engine I use stock needle. There are also the carb slides coming in different sizes, bigger number meaning leaner.

Another thing, is your silencer fresh or recently repacked or has still a old packing? How is your timing set. Both have an influence on how your bike runs.