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05 CRF250 Starting problem has me baffled

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I volunteered to "fix" this bike for my sons friend and its on the verge of beating me....

I got the bike with the symptoms:

  • Was hard to start. Had to push start. Then would run fine.
  • Eventually it wouldn't start at all...
  • The owner replaced the piston and rings. 
  • Stated they checked the valves and were within spec.

When I dug into it, the valves had closed up. I had the head machined and replace the intake valves. (SS valves w/kibblewhite springs). Also replaced the cam chain. 

 

Once back together I still can only get the bike to run by push starting it. I have rechecked valve clearance three times, spot on. It runs good once started but only with the idle turned up. This lead me to suspect the carb slow air jet and pilot circuit. I have since disassembled the carb and "cleaned" it twice. All jets are stock and the pilot screw is set to factory settings. (also installed new air filter) Still no luck. Same symptoms. 

When I cleaned the carb I basically removed all the jets and flushed out with carb cleaner. Is this the best way? 

Any other things I should be trying? Different way to "clean" the carb? I am not sure what to try next. Any help is appreciated. 

 

Thanks,

Bill

 

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Some what complicated IMO and it sounds like its not an AIR or SPARK issue.

Turn the fuel mixture screw to 1-3/4 out as spec'd in the manual. I use an after market one but regardless make sure its installed correctly and there is not a small oring stuck in the carb etc.

Then turn the IDLE screw UP or to the left - There is is no spec for how to set this like the fuel mixture screw so it hard to explain but say 1 full turn from where it is now or maybe more depending.

Then open the choke.

Then give the throttle a couple of twists and leave off.

Pull in the hot start (yes even when the bike is cold) and kick with the bike in neutral.

If the bike starts warm up for a minute, close the choke and adjust idle down as needed

Another option is to pull the seat and air filter after setting the fuel mixture screw and idle and spraying some carb cleaner into the air box/carb. Then try kicking the bike and see if it wants to start and this will help narrow down a carb issue.

Solving a carb/gas or for that matter any other issue is methodical so try and continue your first post during this process if you have more questions.

 

 

 

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Quote

Then turn the IDLE screw UP or to the left

Doesn't clockwise rotation increase idle?

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6 hours ago, michaelchristie207 said:

Yes turning it right will rise the idle 

Yes That was my mistake cus I was thinking about doing this while sitting on the bike and that feels like I'm turning it right :)

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On 6/6/2017 at 9:55 PM, filterx said:

Some what complicated IMO and it sounds like its not an AIR or SPARK issue.

Turn the fuel mixture screw to 1-3/4 out as spec'd in the manual. I use an after market one but regardless make sure its installed correctly and there is not a small oring stuck in the carb etc.

Then turn the IDLE screw UP or to the left - There is is no spec for how to set this like the fuel mixture screw so it hard to explain but say 1 full turn from where it is now or maybe more depending.

Then open the choke.

Then give the throttle a couple of twists and leave off.

Pull in the hot start (yes even when the bike is cold) and kick with the bike in neutral.

If the bike starts warm up for a minute, close the choke and adjust idle down as needed

Another option is to pull the seat and air filter after setting the fuel mixture screw and idle and spraying some carb cleaner into the air box/carb. Then try kicking the bike and see if it wants to start and this will help narrow down a carb issue.

Solving a carb/gas or for that matter any other issue is methodical so try and continue your first post during this process if you have more questions.

 

 

 

Fuel screw is set to 1 3/4 turns. All jetting is factory.

It will start by push starting....after its warmed up as soon as I start turning the idle down, it kills.

One other thing I forgot to mention, and why I think its a clogged/dirty carb, is that its been about 8 months since the first problems started. I have replaced all the gas in the tank.

I once had a very similar issue on another CRF250 that I own. Turns out it was the K&N air filter the I had installed. Soon as I put a regular filter in, starts first kick and idles beautifully. Thats why I tried a new air filter. Thought maybe the old one was to free flowing.

Should I try pulling the carb again and soaking it in something?

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I'll preface this by saying I'm no expert and just throwing out suggestions.

Valves/Cam Chain - are you 100% sure all the valves are in spec and the cam chain is installed correctly?

Idle - So the bike starts when you push but not when you kick it Then with the choke off and bike warm it stalls when you turn down the idle. Are you using a tach to at least set the idle once to 1700 RPM so you know what 1700 RPM sounds like.

I'm sure someone with more experience will have other comments

Edited by filterx

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1 minute ago, filterx said:

I'll preface this by saying I'm no expert and just throwing out suggestions.

Valves/Cam Chain - are you 100% sure all the valves are in spec and the cam chain is installed correctly?

Idle - So the bike starts when you push but not when you kick it Then with the choke off and bike warm it stalls when you turn down the idle. Are you using a tach to at least set the idle once to 1700 RPM so you know what 1700 RPM sounds like.

I'm sure someone with more experience will have other comments

Ive checked the valves (and timing marks) at least three times. I will disassemble again this weekend and take some pictures. I'm a firm believer in a "second set of eyes". Valves gaps were right at spec but will check them again. One good thing is I'm getting fairly quick at taking it all apart and putting it back together...;)

Idle - Yes, just what you said....I am basing the idle off the Works Connection Tach/Hour meter. I can get the rpm's down to about 2500 then it kills. 

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Were you sure to put the little o-ring (#1 in diagram) back on the tip of the fuel screw when you reinstalled it?  It is very tiny and sometimes get stuck inside the carb.  Then you can unknowingly flush it out while cleaning.

 

 

Screen Shot 06-09-17 at 01.15 PM.PNG

Edited by mossman77
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Bump start it and then adjust the fuel screw while running. It's the only way to do it properly and most likely you will not end up at factory specs:

 

 

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Were you sure to put the little o-ring (#1 in diagram) back on the tip of the fuel screw when you reinstalled it?  It is very tiny and sometimes get stuck inside the carb.  Then you can unknowingly flush it out while cleaning.
 
 
593ad8136e8af_ScreenShot06-09-17at01_15PM.PNG.bbd7f1054153a1a1886d556d86fc9b71.PNG


Thanks... I'll double check that tomorrow.

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Bump start it and then adjust the fuel screw while running. It's the only way to do it properly and most likely you will not end up at factory specs:
 
 


Thanks for the video. I'll give that a try first thing tomorrow.
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Did you replace the jets? That sounds like it could be a clogged pilot circuit.

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Personally I replaced the OEM fuel mixture screw with an aftermarket one (and as posted making sure the small top OEM oring was removed from the carb)

Something like this one

Fuel-Mixture-Screw-Red-CRF250-CRF450-CRF

 

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Did you replace the jets? That sounds like it could be a clogged pilot circuit.

I pulled them all out and sprayed them with carb cleaner. I am going to double check the little o ring today as someone suggested earlier.

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Personally I replaced the OEM fuel mixture screw with an aftermarket one (and as posted making sure the small top OEM oring was removed from the carb)
Something like this one
Fuel-Mixture-Screw-Red-CRF250-CRF450-CRF250R-CRF450R.jpg
 

I put one of those in on my 07 crf250. I may steal it off my bike and use it to help fix this kids bike.
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With the idle turned up enough to keep it running turning the fuel screw in and out has little effect. I would think because I'm outside of the slow/pilot idle circuit speed. With the fuel screw at 1 1/2 turns, and the idle up high, it revs and returns to idle quick. As soon as I turn down the idle screw (1/4-1/2 turn. Not much) it idles down and kills quick. Maybe I'll try to upload a video....

 

 

Edited by LongW8

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Idle way too high to set fuel mix screw.

Are you positive that you removed pilot jet and fuel screw when cleaning carb? Clean all those passages well and blow with compressed air? Sounds like you are not getting proper fueling for idle circuit.

Wing that screw out to 3 turns and see what happens.

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14 hours ago, MatthewMCRepair said:

Idle way too high to set fuel mix screw.

Are you positive that you removed pilot jet and fuel screw when cleaning carb? Clean all those passages well and blow with compressed air? Sounds like you are not getting proper fueling for idle circuit.

Wing that screw out to 3 turns and see what happens.

 

Took it all apart again. All the jets themselves seem clear. Does the Slow Jet have a smaller hole part was through? I can push a small copper wire into both ends but not all the way through. I have another slow jet that is the same way from my 07 so I assume that is the way its supposed to be. 

When I spray carb cleaner in the Slow Jet hole in the carb, it comes out the Slow Air Jet hole and around the needle inside the carb at the throttle valve slide.

IMG_3514.thumb.JPG.0aa8a762207dada39411a9d447eab4d2.JPG

When I spray carb cleaner in the Starter Jet, it comes out the small hole in the bottom of the column (see second picture). I don't see any where else it comes out. Is that correct?

 IMG_3513.thumb.JPG.bf9d72207a8df724b813f52a39406bdd.JPG

 

Should it be coming out the small tube shown in the next picture that is just to the right of center or is that the accelerator pump hole. 

 

IMG_3512.thumb.JPG.374916c97478c29f0c98dfb38fe1e66c.JPG

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Well, put it all bake together... same problem. Only will stay running with the idle turned up.

I'm stumped.

What about the throttle position sensor? Could it be set/assembled wrong? I did take it off the first time I took off the carb.

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