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2004 CRF250X jerky snatchy throttle making trail riding difficult for novice rider...advice needed!

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2004 CRF250X jerky snatchy throttle making trail riding difficult for novice rider...advice needed!

 

Hi,

 

I've been riding road bikes for years but having got fed up with the cost and distance for running a race bike on track decided to move into the dirt and having a hoot so far.

 

I bought a used 2004 CRF250X. I'm pleased with the bike, especially now that I have fitted new tyres with UHD tubes rather than the very tired tyres and munched-up old mousses that were fitted.

 

One thing though is making my life very difficult, the bike seems crazy urgent on the throttle particularly for riding in tight, rutted or slippery conditions. I'm using 3rd gear a lot and having to slip the clutch to help the situation - and although I'm an off-road novice I fully understand the concept of throttle control. Even with ALL my attention on it, I'm finding it very jerky. I'm already learning that the smoother the throttle the better the traction - on some climbs on wet chalk I can chug up in 3rd with constant throttle but have started positioning my index finger on the brake lever to help keep the throttle constant!

 

My chain tension is correct.

 

 

A few questions

 

1) The previous owner told me it had the pink wire mod done. I roughly understand the mod as an ignition map change to the 250R and have seen the post regarding the effect on the torque and power curves - but could this affect low TPS throttle mapping? I.e. throttle reponse at low throttle grip positions? The bike has an FMF Q4 exhaust, but I have no idea whether normal or R cams, and I don't know what (if anything) has been done to the carb tuning. Or am I barking up the wrong tree with this thought?

 

2) How would I know if he had fitted a fast action throttle? What is the rotation of a standard throttle so I can check? For my use (learning the ropes and trail riding) a normal throttle will be sufficient. I've seen the G2 tamer which looks great but not cheap to buy from the UK. Plus I'd like to understand what's going on before buying stuff.

 

3) Should I investigate my throttle freeplay? Is this relevant?

 

4) Could it be my carb tuning?

 

5) Any other thoughts?

 

Thanks!

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I have an 05 with the same symptoms.  My thoughts are it is caused by too rich a mixture during the transition from the low speed circuit to the needle, like too rich a slide cut away.  You can check that by slowly opening the throttle and listening to the exhaust note for blubbering. Mine is at about 1/16 throttle.  After a lot of carb tuning it is better. And you will get good at lifting the sub frame and pulling the carb.

 

Couple of thoughts: the OEM jetting is very lean and the AP doesn't squirt at low throttle settings so Honda may have installed a rich slide.  If you rejet the richness shows up.  I've experienced these symptoms riding WRs (which is why I bought an X instead of a WR), and I also had that problem on rejetted XRs,  careful carb tuning was the fix for the XRs.

 

First question, has the carb been rejetted, or what is the current jetting and inlet/exhaust mods?

 

My bike: JD jetting (42 pilot, 158 main, red needle, 3rd clip), CCC mods, Yoshimura exhaust. And my attempts:

Reconnected the pink wire, easy to do.

New spark plug.

Drop the needle one clip.

One size smaller main.

New mid gaskets in carb.

New slide lift arm.

New throttle cables.

Reset TPS to the lower end of the resistance range, (it was set way high out of spec).

New slide lift arm.

Remove the O ring from AP to prevent a squirt when coming off closed throttle.

New needle seat

New float, lowered float level, now less gas out of float overflow.

Stock exhaust with insert

 

I have not replaced the needle jet because I could see no wear using a magnifying glass, and it is expensive.  A worn needle jet is a cause of this condition on XRs.

 

I also had a hanging idle problem which is why I replaced the slide lift arm, the throttle cables, and added an extra turn on the throttle return spring.  Now stiffer than I like so may reduce the spring tension.  Careful when adjusting throttle cables because getting them too tight causes a big increase in cable friction and can cause a hanging idle.  The throttle should quickly snap close  with a sharp clunk from the carb idle stop.  So I also adjust mine for minimum friction in addition to the free play spec. Also cable routing is important to prevent a pinched or stretched cable, the Honda Service Manual has several cable routing diagrams. 

 

I routed the float overflow hose to under the gear shift lever so I could check for overflow, I had frequent gas overflow with stock float level so I replaced the float and needle, then lowered the float level a bit.  I made a float level gage from some clear plastic sheet.

 

I also installed a Vapor so I could check engine speed, and a J&D remote mixture screw so I could make adjustments while riding. Leaning the idle mixture helps the problem but creates a lean mixture for other conditions, which is why I dropped the needle and reduced the main jet one size.  I have not tried going back to the stock 40 pilot.

 

The bike is better but I now have a bog at large throttle openings.  Next step is an O2 sensor and data logger to check mixtures.

Maybe I'll lower the float level to 8.5mm and go back to JD jetting recommendations.  

 

One additional thought, are your valve clearances within spec?  Tight intake clearances can cause hard starting and difficult idling.

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I think you may be over-thinking this.  Unlike a street bike where you let out the clutch and go and then just use it to shift, on a dirt bike,you are using the clutch almost 100% of the time.  Use the clutch to modulate your traction, not the throttle.  Use the clutch to take the jerkiness out of the throttle on/off transition.   Unless you are on an open road, you will have your fingers over the clutch all the time.  That is why the auto-clutch is making big inroads in dirt applications and they do not sell them for street applications.

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I've checked the throttle. It is closed to fully open in 1/5 of a turn. I think this is a quick action motocross throttle? Could this be why its so difficult to modulate in tricky, slippery technical stuff?

 

I understand about using the clutch a lot of the time, but feels like having to constantly tame the fierce response, even in 3rd gear and even on a 250 'ideal for new riders' bike feels a bit odd? Its very energy sapping!

Edited by Chipstix

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Just checked my stock throttle rotation.  Its just a bit less than 1/4 rotation from idle to wide open.  Never had my hands around a quick throttle, but...  Good read guys. Chuck...what altitude are you jetted for?

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Thanks, that's helpful!

 

I'm therefore interested in the G2 ergo kit for my bike. Based on the standard throttle rotation from idle to wide open is just under 1/4 turn, if I purchase a G2 ergo kit, will I need to change/update my throttle cables? I.e. will the 1/5 turn quick action currently fitted have been paired with non-stock length throttle cables?

 

I think the US domestic price for the G2 kit is great, but the shipping and import to the UK really push it up a lot unfortunately.

 

C.
Edited by Chipstix

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Looking at the G2 throttle tubes, I'd be surprised if you ran into any issue with throttle cables.  There's a fair amount of adjustability in the cables, so...  However, I've not had any direct experience with the G2 tubes.  I see their Dirt Tamer and their Street Tamer.  The Dirt Tamer apparently rolls to half throttle just like a stock tube, then "quickens".  Your tube with a rotation of 1/5, may well also be stock.  As indicated, my stock is a bit less than 1/4.  Is that what you're observing as a 5th...I don't know?  The description of the Street Tamer appears to soften the initial stock twist/response.  Never dealt with G2, but I recommend that you call or email them directly and troubleshoot your situation. 

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I'll throw an option out for you on this- what gearing are you running? either go UP a tooth on the countershaft sprocket or down 2-3 on the rear sprocket and see how you like it. Did this to my wife's 250X and daughter's 250X and they both said the symptoms you described went away. We ride fairly technical and slow singletrack, as well as faster two track- haven't had any complaints on the gearing being too tall by either of them. They both are competent riders, and use the clutch often.

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@UnkleKnobbly, thanks - have emailed G2. I think my throttle is 'significantly less' than a 1/4 if that makes sense. Perhaps I'll measure it, but 1/5 is 72deg and perhaps it even looks less than that. I think it may be a motocross race style. I saw the street tamer, but by the time I pay all the shipping and import I'm leaning towards the 'kit' which has stock cam, 10% gentler lead in than stock and 20% gentler lead in than stock cams. I would hope this gives me future proofing to some degree as I increase experience or want to experiment.

 

thanks redhurricane, that is an interesting option. Are they running standard range throttles, fast action or a G2 cam type arrangement? I do wonder though if playing with gearing with a really tight throttle range is perhaps coming at it from a different direction than I'd like because I would like to more easily modulate the all important power. I guess a new sprocket could be less expensive and similar effort to fit.

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Both their bikes are OEM throttle tubes. When they both complained about the snappiness of the bike I made the suggestion to just carry more speed. An hour later I was buying sprockets online. It's a fairly cheap option compared to throttle tubes, worth a try in my opinion.

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I think you may be over-thinking this.  Unlike a street bike where you let out the clutch and go and then just use it to shift, on a dirt bike,you are using the clutch almost 100% of the time.  Use the clutch to modulate your traction, not the throttle.  Use the clutch to take the jerkiness out of the throttle on/off transition.   Unless you are on an open road, you will have your fingers over the clutch all the time.  That is why the auto-clutch is making big inroads in dirt applications and they do not sell them for street applications.

 

X2.  Even an XR 100 can have a jerky off-idle response.  Don't discount the above advice.  I've used it for years to tame even the nastiest powerbands. It's just a nudge here and there, but becomes instinctive quickly. You can use it to both mellow your acceleration or intensify it.  No, I do not burn through clutches.  Yes, you do want to jet properly.  Clutch feed is a useful technique and can really improve your riding experience.

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When I was a noob on my 250X, I too had a jerky response. It would start off knda ok, then snap my neck back a little as it hit, even though I'd not really turned the throttle but a little bit more. Once I got it jetted correctly, all was good. Prior to that, I was told to get a different throttle cam. Not needed at all and had nothing to do with clutch.

 

42 or 45 pilot jet are correct for that bike.  What's in yours and what size is your main jet, what needle is in it and where is the needle clip?

 

Thats where I would start. It should be a simple fix.

 

If that doesn't do it, then you'd have to get  a little further into to see what the prior owner did with the accelerator pump and if it still has a leak jet and if so, which one. You'd need to pull the carb bowl off to see about that.  Hopefully simple rejetting is the solution.

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two questions:

 

what gearing is one the bike (front/rear sprocket tooth count)?

what size tire (tyre) are you running on the bike?

 

when changed my 250X to 13/51 (14/53 is stock) i threw on an old 100/100-18 tire instead of the 110/100-18 that i usually run (not really thinking the diameter difference would effect much) - this made the bike very jerky.  switching back to the 110/100-18 tire smoothed everything out.

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Just checked my stock throttle rotation.  Its just a bit less than 1/4 rotation from idle to wide open.  Never had my hands around a quick throttle, but...  Good read guys. Chuck...what altitude are you jetted for?

Sealevel plus a few.

 

Gearing is 14/51 but I'm running a 4.00R18 tire which is a bit bigger than a knobby, and has lots of traction. I tried a 13 and it made things worst.

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two questions:

 

what gearing is one the bike (front/rear sprocket tooth count)?

what size tire (tyre) are you running on the bike?

 

when changed my 250X to 13/51 (14/53 is stock) i threw on an old 100/100-18 tire instead of the 110/100-18 that i usually run (not really thinking the diameter difference would effect much) - this made the bike very jerky.  switching back to the 110/100-18 tire smoothed everything out.

 

Hi guys,

 

Have checked: my front sprocket is 14 teeth, with 53 teeth on the rear

 

My rear tyre is Mitas X Treme 754 120/90-18

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The touchy throttle has also frustrated me.  I have learned to live with it.  One way is by slipping the clutch.  Another way is by repeatedly blipping the throttle in tight conditions, instead maintaining just a little throttle.

 

Also, another option that I don't believe has been mentioned yet is a heavier flywheel weight.  This should make it less jerky.  But, the trade off is it will be less responsive it you are trying to lift the wheel over a log.

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Dang guys! Get the bikes jetted right and it will be GONE!! Don't worry about tires and other stuff that won't cause it unless you're way out to left field with it (e.g. gearing)?  Until the motor has the proper jetting, it simply won't run right and you're talking about an issue of throttle response.

 

Do you know your jetting?  Where is it in comparison to this::

 

55 LJ

AP link wired or O-ring mod (but o-rings break, hence why I went to a wire)

45 PJ

Stock needle, clip on 3

148 MJ

Snorkel removed from airbox

Stock exhaust (we've since pulled out the baffle and its still fine)

05 R cam

 

Ok...ok...since you're likely kinda new at this, Don't worry about the leak jet or the cam. You can get the pilot jet and main jet out of the carb without removing it from the bike. Twist the bottom of the carb to left. Now, you can also get the needle out without removing the carb. Remove the motor mounts that are in the way and twist the bottom of the carb to the right.  Its a pain first time for sure. You can do it though if you want to.  I can change MJ and PJ in 10 minutes...sometimes less if I get lucky on the reinsertion.

 

A key to jetting with carb on bike is a small ratcheting socket that can unscrew and tighten jets through the carb's drain hole.  I'll search for a thread with a pic of the magic tool and will be back with it soon.

Edited by dmac1

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Heres a couple tools that will make on the bike jetting a snap:

 

Husky ratchet and socket kit, part number on the package is 165152, but the number on the tool itsself is 66604. Last time I looked, not all Home Depots stock this tool because another one I went to didn't have it.

 

IMG_3166.jpg

The Husky tool comes with a handful of short screwdriver bits AND a short 1/4" drive socket extension which fits in the 5/16" box end!

I located a small flathead screwdriver bit at Ace Hardware. It is the smallest I could find and the blade measures 5/32" wide. It is part number 2059327

 

IMG_3164.jpg

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Hi All,

 

Thanks - lots of helpful advice.

 

 
I've not got much experience working with carbs, but I have friends around me that have. A few things that are going through my mind though before I start playing with the carbs....
 
1) When I say jerky, what I really mean is super sensitive on the throttle. I.e. tonnes of torque with minimal throttle input. To me, it doesn't feel like the fuelling isn't right because when pulling it has
a) loads of pull, very responsive
B) not particularly noticed stong Hydrocarbon smell or misfire/pops/bangs
c) no problem starting from cold
d) no problem starting when hot (even though there is no hot-start lever cable present!)
e) in steady state throttle position, the drive is direct and accurate
 
2) I don't know the full history of the bike. Its a 2005 model year and whilst the guy I bought it off was very helpful, he hadn't had it since new. Along the line its had lots of things done (e.g. excel rims, talon hubs, FMF Q4 exhaust, "pink wire mod") so my point is for all I know the bike has an R-cam in and the carbs have been fully set-up. I don't have the info to say for sure. Which is why I'm keen to check out all other possible root causes first.
 
3) My twist grip is definately shut to wide open in less than 1/5 of a turn. I think 1/4 turn is standard? Plus, my throttle might be an extra-aggressive cam profile, i.e. quick action and non-linear. Surely this is a major factor in what I am experiencing? I'm looking seriously at the G2 ergonomics cam system (which by the way I am assuming are make and model specific as otherwise there's a decent used one for sale on ebay.co.uk which is from a Ducati 1198!)
 
4) My 14teeth, 53teeth gearing - is that 'standard' CRF250X?
 
C.

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Just for clarity: 14/53 gearing is factory original.

Gearing, tires, or cam profile will impact the symptom but will not resolve the causing issue. Carburetors work in multiple circuits that overlap a little at the edges as it "hands off" from one to the next. Your jerky throttle is caused by poor transition from idle to 1/4 throttle, and has nothing to do with how it runs above that. It can be fine in spots, lean in spots, and rich in spots... All at the same time. Once you find the sweet spot in your carb tuning, it will smooth out and run great anyway you twist (or don't) the throttle.

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