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CRF250x Carby Massive Idle Issues

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Hi,

I am having massive issues with my CRF250X carby and hope that maybe someone can help. I have searched this forum, others and google for weeks but still cannot come to solve the problem.

I'll try to best describe it... it will be long.

The problem is the idle, it just wont stay steady, it's either about 2300rpm or drops to about 1250rpm and then dies.
Adjusting the idle rpm knob even just a tiny little pinch makes it switch from ~1250rpm to suddenly screaming at ~2300rpm.

Work done so far, all in last 3 months (been for a 3 hour ride over this period):
-Valves checked & all in spec (by me, a generic moto mechanic & by Honda too)
- Compression @ 68-70psi
- NEW rubber boot fitted between carby and head
- Carby off and cleaned 3 times (my me, a generic moto mechanic & by Honda too)
- ALL new genuine jets fitted
- All new gaskets/o-rings/float valve fitted
- Also replaced floating valve rubber and the slide plate too
- Hot start closing properly

It still runs like crap at the idle though and it has me absolutely stumped as everything that can be replaced has been.

I ride from sea level and up to 300m by the coast in Perth, Australia.

Myself + the mechanics have tried jetting from stock and all the way through to 50pilot and 160main with various needle clip and fuel screw settings too.

To get the bike to remotely idle at a normal style requires a 50pilot jet at 2.5-3 turns out and it's still popping and crackling a little at the idle too. This is with a 160main and needle clip 4th from the top. I know it's not right but that's what it needs simply to actually idle.

Bike is stock apart from full FMF Q4 system and a high flow air filter.

Sometimes the idle will hang for 5 seconds, sometimes it will hang for 20 seconds (screaming at near 2300rpm)... then it just suddenly drops and coughs at about 1250rpm for like 3 seconds and then dies.

I just dont know what else I can replace/try/do to get this thing going?

Buy another complete carby?

Any help would be much appreciated, me posting and asking for help is always a last resort as I always research everywhere else possible.

Thanks all,
Simon

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FloatingValve.jpg

 

 

 

That's all I got...

 

:ride:

 

 

 

 

 

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Simon,

 

  Tough problem..assuming you don't have a mate with a 250x that you can switch carbs with?   Would narrow it down quick.

 

  Sounds like air is getting in somewhere....

 

The simple stuff to check:

 

1. What Rick said<g> - Top gasket on the carb and the slide gasket being installed correctly.

2. The plastic nut on the hot start - they do crack and it's easy to miss.

3. **** REALLY **** make sure there is not more than one o-ring in the fuel screw hole.   Posting just the other day; three o-rings came out, and there was a 4th in there causing an idle problem!

4. Replace the plug.  Sounds weird I know, but I've seen some very odd problems in the past when the insulator breaks away from the shell and cracks.   Also while there, make sure another sealing washer is not down in the hole.

5. Pull the pink wire (the "pink wire mod").   That basically disables one leg of the TPS.  See if it makes a difference.

 

 Beyond that, when the carb was cleaned, was it fully disassembled each time and what was it cleaned with?

 

 If carb cleaner, which melts rubber and plastic, then I'd be concerned over the mid-body gaskets.  Normally you don't take a carb apart here because the gaskets were not available separately.  If those gaskets got trashed or the slow circuit was plugged there, the carb was trash.  They are available now.  Something you may want to consider.

 

Remote possibility: CDI is varying the timing on you.

Real remote possibility: crack in the cylinder head.

 

But one thing you didn't include in your post (which was very good by the way....lots of info), when did this start?   Did it come on gradual or all of a sudden?  What (if any) work was done recently?  Outside of the idle, what does it run like?

 

Jim.

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+1 on all of the previous as a hanging idle is usually from a lean mixture caused by an air leak, which is why you needed the #50 pilot.

 

However I've found one other cause of hanging idle and that is the throttle cables and/or the twist grip.  Often the only thing needed is a good cleaning and some dry film lube.  When releasing the twist grip with the engine off you should hear a nice loud clunk from the throttle stop screw. I like to check these first since it is easier than pulling the carb.

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Simon,

 

  Tough problem..assuming you don't have a mate with a 250x that you can switch carbs with?   Would narrow it down quick.

 

  Sounds like air is getting in somewhere....

 

The simple stuff to check:

 

1. What Rick said<g> - Top gasket on the carb and the slide gasket being installed correctly.

2. The plastic nut on the hot start - they do crack and it's easy to miss.

3. **** REALLY **** make sure there is not more than one o-ring in the fuel screw hole.   Posting just the other day; three o-rings came out, and there was a 4th in there causing an idle problem!

4. Replace the plug.  Sounds weird I know, but I've seen some very odd problems in the past when the insulator breaks away from the shell and cracks.   Also while there, make sure another sealing washer is not down in the hole.

5. Pull the pink wire (the "pink wire mod").   That basically disables one leg of the TPS.  See if it makes a difference.

 

 Beyond that, when the carb was cleaned, was it fully disassembled each time and what was it cleaned with?

 

 If carb cleaner, which melts rubber and plastic, then I'd be concerned over the mid-body gaskets.  Normally you don't take a carb apart here because the gaskets were not available separately.  If those gaskets got trashed or the slow circuit was plugged there, the carb was trash.  They are available now.  Something you may want to consider.

 

Remote possibility: CDI is varying the timing on you.

Real remote possibility: crack in the cylinder head.

 

But one thing you didn't include in your post (which was very good by the way....lots of info), when did this start?   Did it come on gradual or all of a sudden?  What (if any) work was done recently?  Outside of the idle, what does it run like?

 

Jim.

Hi Jim,

 

Great reply.. thanks for some extra pointers.

 

The hard part is I bought this bike not running, 2004 with 1800 original km. It has been sitting in a factory for 5 years covered in dust. The problem was there as soon as I got it going so I cant diagnose when/how it started.

 

- The bowl o-rings, top casing o-ring & the o-ring on the cover to access needle are all brand new and greased up, seated 100% as I could see potential issues there

- Plug is a brand new irridium, but I can change out for the old one to try... yes

- The hot start nut looks ok but even if it were cracked, the brass plunger is still sealing perfectly so that should be ok?

- O-Rings on fuel screw... I triple checked this every time it was pulled down and it's only got the 1 o-ring in there

- I'll try the "pink wire mod" thanks...

- These mid-body gaskets... they could well be a culprit and something that I have not looked at (will be now)

 

Either way, the carb has to come off again (I hate this job)... there's no doubt about that.

 

Thanks for the tips and I'll let you know how I go.

 

Simon

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Simon,

 

Few things:

 

1. As Chuck said, check that your cables are not being pulled.  Make sure you move the bars lock to lock.

 

2. On the hot start, if the nut is cracked, it will let air in past the plunger.

 

3. Venting - doubt this has anything to do with it, but leave the cap loose and check that the carb vents are open.

 

4. Make sure you have a good strong flow of gas from the tank at the carb.  Since it's been sitting for so long, it's possible that either the fuel screen in the tank has collapsed, or the inside of the fuel line is breaking up/collapsing (in fact if you haven't already changed it, I would).

 

5. Double check the float level

 

6. If you have not done so, replace the emulsion tube (what the needle rides in).   They tend to wear into an oval.

 

7. On the plug, yes just swap it with something for a bit.  Really doubt it's the problem, but like I said, I've seen some weird problems when the insulator cracks.   Generally though, a problem here would happen across the RPM range and from your posts, it's sounds like it's just the idle that is the issue, which points back to the carb.

 

  But I still haven't seen where you say how it runs otherwise and if this is your only problem.

 

  At this point, I'd put it back together and see where your at.   If it's still doing the same thing, then I would think it would be the mid-body gaskets.  I say leave this to last because it still can be difficult to find the rights ones.  Not sure who you have your way to buy these from, but I would look to James Dean (JD) Jetting and verify with them that they have the right gaskets before you take it apart.  By the way, here's what were talking about:

 

http://www.jdjetting.com/xcart/product.php?productid=132

 

 Note this may not be the one you need, so check with who ever you buy it through that your getting the right one.

 

 If you get it apart and don't have the right ones, then you'll end up having to make your own or will be looking at another carb.

 

Jim.

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Tricky question... I've had 5 CRF250's and find that this tends to happen on all of them once they get old enough (up around 200 hours).  I'm not sure exactly what the cause is, but I suspect the pilot air circuit basically gets some crap it  over time.  What then happens is you keep lifting your idle to compensate... eventually you start lifting the slide high enough with the idle knob that it starts to trip the TPS which leads to hanging idle...  sometimes revving it's titts off and sometimes wanting to stall.  I find that a new float valve or all new slide does help alleviate it somewhat.  I usually sell the bike and get a new one :D

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