01 CR250 cutting throttle slide

[YZhallsme]

Originally Posted by VAL

Man you are so close. Dont mess with the needle if shes running good mid to top end. You should be able to balance between the pilot, air screw and idle screw. Also remember that these are two strokes, not known for their stellar bottom end. I was able to get a little more grunt with an 11oz flywheel weight. It smoothed out the choppy off idle response.

Well I know it isn't a 4 stroke nor will it ever be, but I can tell this is a darn good motor with a wide powerband that will pull very strong from early in the throttle right on thru wide open. I have gotten closer but I havn't found a solution to the stutter with pilot, airscrew and idle adjustments. Here's a link to a mikuni guide I was looking at the other day[Only registered and activated users can see links. ]. Unfortunately it doesn't go into the individual parts of a needle and the throttle range they cover, like straight diameter 0-1/4 throttle, or taper, taper starting point or clip position. It does indicate that the area from 0 to 1/4 throttle (where my stutter occur's) is governed by many different parts of the carb. I don't think I can go any leaner on the pilot so I've ruled it out. I see needle straight diameter would address this area perfectly without affecting anything else but since I'm using the red needle (largest diameter of the two) I can't go there. I could try a leaner needle jet (nozzle) effective from 1/8 to 3/4 throttle or a leaner clip position, effective from about closed to wide open but those may, as you aluded to, have a negative affect in the mid throttle range. I don't have a leaner nozzle and I've allready tried red clip #2 which produced a bog just above idle and surged rather badly during deceleration with the throttle chopped (both signs of being lean). It looks as though the throttle valve cutaway, effective from about closed to 3/8 could be the ticket also. Honda doesn't offer anything other than the stock 4.0 cutaway, I did find a 5.0 (leaner I think) listed specificly for the 01'-03' CR 250 at sudco's website, havn't figured out the price on that yet. Looks like yamaha offers both a 4.5 and a 5.5 for a 98' YZ 125 but I'm uncertain if they would fit my carb, not to mention it's $100!! Filing away at the stock throttle valve would be the cheaper route then, but I"ll save that for later. For now I went with the other cheap option, a washer from ace hardware, 4 cents. I used it to shim the needle 1/2 clip position and upped the pilot one size. So now it's red needle clip #2.5 and a 25 pilot. A quick spin around the neighborhood for warmup, then on to the rec. center parking lot for a couple airscrew adjustments and a few closed to 1/4 throttle blips, then down the street for one wide open blast, I know it's not a good test and that I've been fooled by this trial run before but I must say I'm pretty excited, it produced some good results. No sputter, smooth return to idle, front lifts with just the throttle, best top speed to date. Now I just need to get her in the dirt where she belongs and find out for sure if this is real or just a dream!

[YZhallsme]

Update- @ 8,000' 65*and dry
370main, 25 pilot, JD red clip #2.5, airscrew seemed best around 1 3/4 to 2 out.

Got her out on the trail this past weekend and must say this setup worked really good. The 0-1/4 stutter is finally gone and it still runs well through the rest of the throttle range. The only dissapointment if I could call it one, was I didn't see a reduction in spooge. Maybe it will take another ride or 2 to clean up or maybe I'll learn to live with it? Unfortunately something went wrong with my computer so I can't give a mileage report. I'd like to thank everyone here for their input/help especially VAL who introduced the idea of using the idle screw for tunning purposes. Something I'd never really considered before! It was very effective in eliminating the surge during closed throttle decel plus didn't have the negative affect of a diminished throttle response, which was the case when I tried airscrew/pilot adjustments.

[VAL]

Glad to hear you have her running the way she should.

[junteschan1]

Originally Posted by YZhallsme

Update- @ 8,000' 65*and dry
370main, 25 pilot, JD red clip #2.5, airscrew seemed best around 1 3/4 to 2 out.

Got her out on the trail this past weekend and must say this setup worked really good. The 0-1/4 stutter is finally gone and it still runs well through the rest of the throttle range. The only dissapointment if I could call it one, was I didn't see a reduction in spooge. Maybe it will take another ride or 2 to clean up or maybe I'll learn to live with it? Unfortunately something went wrong with my computer so I can't give a mileage report. I'd like to thank everyone here for their input/help especially VAL who introduced the idea of using the idle screw for tunning purposes. Something I'd never really considered before! It was very effective in eliminating the surge during closed throttle decel plus didn't have the negative affect of a diminished throttle response, which was the case when I tried airscrew/pilot adjustments.

Is the needle jet still an S-4 per your above specs?

[YZhallsme]

Originally Posted by junteschan1

Is the needle jet still an S-4 per your above specs?

Yes it does have the S-4 and that is still the best I've come up with to date. I actually received some slides that have been cut by someone else. Experiments with them have been minimal, and so far not good. I'll keep trying and post later if I find something I like. I'm wondering if you've found a setup you like? or should I say, that's worked the best for you so far?

[junteschan1]

Originally Posted by YZhallsme

Yes it does have the S-4 and that is still the best I've come up with to date. I actually received some slides that have been cut by someone else. Experiments with them have been minimal, and so far not good. I'll keep trying and post later if I find something I like. I'm wondering if you've found a setup you like? or should I say, that's worked the best for you so far?

YZhallsme,
I tried that S-4 nozzle finally w the following combinations-400 main; 30 pilot;
A/S-3.0 turns out; 6beh173 oem needle at 2nd notch;32-1 ratio; mobil 2t;
3000 ft asl; at 75-80 deg F temp.
At a particular time with prolonged 3/4 to full throttle for about 10 min was running really strong & crisp and as soon as I reached my destination,
decided to let engine cool down & I smell a metallic burn coming from the engine.
Could it be that engine is running too lean there was not enough gas/oil cooling the engine running at such very high rpm.
Dont you notice the same thing with your bike that burnt metal....just after running the same...
I know my a/s is off at 3.0 turns so next test ill try 2.0 or less for a richer mix...thanks for any info....

[YZhallsme]

Originally Posted by junteschan1

At a particular time with prolonged 3/4 to full throttle for about 10 min was running really strong & crisp and as soon as I reached my destination,
decided to let engine cool down & I smell a metallic burn coming from the engine.
Could it be that engine is running too lean there was not enough gas/oil cooling the engine running at such very high rpm.
Dont you notice the same thing with your bike that burnt metal....just after running the same...
I know my a/s is off at 3.0 turns so next test ill try 2.0 or less for a richer mix...thanks for any info....

No I haven't noticed that, but it could be due to many variables. I know the JD red needle starts out richer (smaller) on the straight diameter than our stock needle (@ 2.68mm vs. 2.73mm), at some point it looks like the stock needle might catch up and then run richer at the other end? Also I rarely if ever see wide open runs for more than a minute, if even that. It's possible that the s-4 with the stock needle is too lean, if I remember correctly most people using the stock needles and a smaller nozzle were using around an s-7. Are there any other signs of being lean? Did you try a richer clip position with the s-4?

[VAL]

Hey Guys,
Sorry to butt in here, but what did the plug look like? Was the burnt metal smell coming from the exhaust pipe or from the general area of the motor?
Does you bike have a spark arrestor and if so, what dose it look like after a long run. I have a XR650 that after a long hard run, the mesh of the spark arrestor is glowing.

Andy

[junteschan1]

Originally Posted by YZhallsme

No I haven't noticed that, but it could be due to many variables. I know the JD red needle starts out richer (smaller) on the straight diameter than our stock needle (@ 2.68mm vs. 2.73mm), at some point it looks like the stock needle might catch up and then run richer at the other end? Also I rarely if ever see wide open runs for more than a minute, if even that. It's possible that the s-4 with the stock needle is too lean, if I remember correctly most people using the stock needles and a smaller nozzle were using around an s-7. Are there any other signs of being lean? Did you try a richer clip position with the s-4?

Using the S-4 with the oem 6beh173 needle, and A/S at 2.0 and needle notch on 3rd probably would be the variables I'd try...Ill post my findings after...
thank you....

[junteschan1]

Originally Posted by VAL

Hey Guys,
Sorry to butt in here, but what did the plug look like? Was the burnt metal smell coming from the exhaust pipe or from the general area of the motor?
Does you bike have a spark arrestor and if so, what dose it look like after a long run. I have a XR650 that after a long hard run, the mesh of the spark arrestor is glowing.

Andy

Hey val,
Good question....where the burnt metal smell was coming from ...general engine area or exhaust pipe....i was sitting on the bike while in idle, I should have
checked...Yes i have a spark arrestor and of course oil spits were on my rear wheel & suspension arm and rear caliper area wc I think would be normal for a prolonged 3/4 to full throttle use for about 7 min....let you know more after some more tests...thank you.

[junteschan1]

Originally Posted by junteschan1

Hey val,
Good question....where the burnt metal smell was coming from ...general engine area or exhaust pipe....i was sitting on the bike while in idle, I should have
checked...Yes i have a spark arrestor and of course oil spits were on my rear wheel & suspension arm and rear caliper area wc I think would be normal for a prolonged 3/4 to full throttle use for about 7 min....let you know more after some more tests...thank you.

Also, the jet needle 6beh173, is this generally leaner or richer than a 6beh273 needle?

Finally, for those using a S-4 needle jet on a mikuni tmx 38 mm, what sort of needle do you combine it with...i mean needle specs....thank you...

[VAL]

Originally Posted by junteschan1

Also, the jet needle 6beh173, is this generally leaner or richer than a 6beh273 needle?

Finally, for those using a S-4 needle jet on a mikuni tmx 38 mm, what sort of needle do you combine it with...i mean needle specs....thank you...

Sorry, cant help you with the stock needles, I am running the JD set up, they were the ones that sent the 4 s nozzle to complement their needles.

[YZhallsme]

Originally Posted by junteschan1

Also, the jet needle 6beh173, is this generally leaner or richer than a 6beh273 needle?

The 6beh273 is 1/2 clip position richer than the 6beh173. In other words, these two needles straight diameters and tapers are the same. The difference is that the tapers on the 273 start 1/2 clip position sooner (closer to the top of the needle) than the 173. So then the 273 in clip #3 would be the same as the 173 in clip #3.5 (if there was such a position). The clip position has an effect on the area from @ 1/8 to 3/4 throttle.

The last two numbers of the O.E.M. 01' Cr 250 needles refers to the needles straight section diameter, 73 = 2.73mm. Honda offers them in .01mm increments from 2.70mm (smallest diameter=richest) to 2.76mm (largest diameter=leanest). So you have 6beh170 thru 6beh176 and the 1/2 clip richer needles 6beh270 thru 6beh276. The straight diameter has an effect from @ closed to 1/4 throttle. Hope that made sense!

[junteschan1]

Originally Posted by YZhallsme

The 6beh273 is 1/2 clip position richer than the 6beh173. In other words, these two needles straight diameters and tapers are the same. The difference is that the tapers on the 273 start 1/2 clip position sooner (closer to the top of the needle) than the 173. So then the 273 in clip #3 would be the same as the 173 in clip #3.5 (if there was such a position). The clip position has an effect on the area from @ 1/8 to 3/4 throttle.

The last two numbers of the O.E.M. 01' Cr 250 needles refers to the needles straight section diameter, 73 = 2.73mm. Honda offers them in .01mm increments from 2.70mm (smallest diameter=richest) to 2.76mm (largest diameter=leanest). So you have 6beh170 thru 6beh176 and the 1/2 clip richer needles 6beh270 thru 6beh276. The straight diameter has an effect from @ closed to 1/4 throttle. Hope that made sense!

It does make sense of course so now i just have to line up needles that i have to try on that S-4 nozzle.
YZhallsme thank you and of course VAL for your immediate reply....

[YZhallsme]

Originally Posted by junteschan1

It does make sense of course so now i just have to line up needles that i have to try on that S-4 nozzle.
YZhallsme thank you and of course VAL for your immediate reply....

junteschan1 did you decide against the stock needle with the S-4? I'm wondering cause I just pulled the carb, removed the JD red needle and thought I'd give the stocker in clip#3 a try.

[junteschan1]

Originally Posted by YZhallsme

junteschan1 did you decide against the stock needle with the S-4? I'm wondering cause I just pulled the carb, removed the JD red needle and thought I'd give the stocker in clip#3 a try.

YZhallsme,
Sorry for the late reply. Yes, I still have the S-4 installed combined w the 6beh173 oem needle on 3rd; I still will have to test the same with the A/S
2 turns out after which I go to try 4th clip....
I have yet to find the time maybe this month should be better.
How about your end? have you tested yet lately compared to the jd kit.
Thank you.

[nutty]

I bought the jd kit for a 02 CR 250 and it came with the S-4 nozzle. I could never get the bike to run right with the S-4 installed. I tried the red neddle,blue needle,390,400,410 main jets and all differant needle clip positions. It ran the best with the blue needle in the 3rd position with a 410 main but would hardly idle. I put everything back to stock (S-9 & stock needle) and 400 main and it runs pretty good. Im still playin with it though.

[junteschan1]

Originally Posted by nutty

I bought the jd kit for a 02 CR 250 and it came with the S-4 nozzle. I could never get the bike to run right with the S-4 installed. I tried the red neddle,blue needle,390,400,410 main jets and all differant needle clip positions. It ran the best with the blue needle in the 3rd position with a 410 main but would hardly idle. I put everything back to stock (S-9 & stock needle) and 400 main and it runs pretty good. Im still playin with it though.

nutty,
what size pilot jet did you install and what other specs?
Have you followed YZshallme or VAL's specs also?

[nutty]

I followed the jd instructions word for word. For the 02 it calls for the stock pilot whitch is 32.5. I played with the air screw and it didn't really affect anything. Im in Mesa,AZ at about 1700' elev. Im in the process of breakin the bike down for its annual pm work so it might be a while before I get to play with the jetting again. Im gonna start with a new top end cause its still on the original piston and ring set!

[cr2504life]

Originally Posted by nutty

I bought the jd kit for a 02 CR 250 and it came with the S-4 nozzle. I could never get the bike to run right with the S-4 installed. I tried the red neddle,blue needle,390,400,410 main jets and all differant needle clip positions. It ran the best with the blue needle in the 3rd position with a 410 main but would hardly idle. I put everything back to stock (S-9 & stock needle) and 400 main and it runs pretty good. Im still playin with it though.

I also just installed the JD kit for an 02. I haven't played with it but it still has the same symptoms as the stock setup. Very poor response at 0-1/4 throttle, it will even load up (running rich). It started to rain so I never got to play with the air screw or anything.