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2005 YZ250 Impossible Idle

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Now I think I grasped the idea of the search function but it has left me empty handed for an answer. My yz250 will NOT idle indefinitely. When setting the idle and mixture screw the best I ever get the bike to "Idle" is at a high idle and then it will for some reason miss a few beats and stall after 10-15 seconds. If I wanted it to keep running the idle would need to be set extremely high to keep it from dying off. While setting the idle it seems like I will be slowly decreasing off the high idle and then all of a sudden a 1/32 turn of the idle screw and my bike falls on it's face and stalls and no matter how much I keep it alive with the throttle it will stall when let off. I have tried 45-48-50-52 pilot jets and I have checked to make sure my choke plunger is all the way down. The slide is not hanging up from what I can tell and is fully seated, and there is no groove or notch at the bottom where the idle screw meets the slide. The conical end on the idle screw is flawless. I have sprayed brake cleaner on all boots and reed surfaces during operation with no change. I checked the seal behind the flywheel and sprayed some brake cleaner in there during operation with no spike in rpm. Any input?

Bike Setup

2005 YZ250

Stock motor

VF3 reeds

175 main

48 pilot (tried 45, 48, 50, and 52) The 48 gave me the longest high idle before stalling.

Needle N3EW

Needle clip position 1

Fuel Mixture 40:1 Yamalube 2R (91 Octane)

Timing set with dial indicator 2 degrees retarded

Gnarly Pipe W/ Power Core 2 Silencer

Elevation 1300ft

Temperature 80-90 degrees right now.

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My float height is set according to the manual, do you think I need to reset this again?

Capture.PNG

Edited by YZ250TRAIL

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1 minute ago, S.O.A.N.Z said:

hows the wear on the slide ?

overly worn can cause erratic idle problems

My slide seems to be fine? Is there a way to check if it is overly worn? In my opinion it is fine, I also had a second opinion from a well experienced Yamaha mechanic and he looked at the idle screw seating area first and said that it was flawless and my slide looked okay as well. Would pictures of the slide help any?

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Check your reeds for air gaps around each petal,

even brand new those VForce are problematic.

 

If you still have the old reeds and cage, it's worth a test trying those.

Edited by mlatour

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33 minutes ago, mlatour said:

Check your reeds for air gaps around each petal,

even brand new those VForce are problematic.

 

If you still have the old reeds and cage, it's worth a test trying those.

I will take a look this evening at the reeds, the previous owner never gave me the oem reeds unfortunately... Would faulty reeds only act up at lower engine speeds? 

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Recheck the black idle screw, it's plastic... After the slide has beaten it down in one position it flattens out. 1/32 of a turn sounds about the problem, in addition to mentioned above.

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24 minutes ago, P84ONE said:

Recheck the black idle screw, it's plastic... After the slide has beaten it down in one position it flattens out. 1/32 of a turn sounds about the problem, in addition to mentioned above.

I will recheck for a flat area on it, it hadn't looked damaged or worn to me when I originally checked it?

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A engine needs to be airtight in order to Idle well, I'm sure you know this but you don't want to idle a bike indefinitely. I think mine would 10 months a year but in the peak of the summer it seems to idle good for 15 seconds or so then starts to drop. I don't worry about it, I think it's pretty normal. If you have the reed off make sure you seal it on all surfaces good when you reinstall it.

I am at 1300 feet 80° right now and I am very happy with 45 pilot, N3EW-3, 40 power jet, 175 Main. Your needle sounds very lean to me.

 

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Is there any tolerance for air gap on the reeds? There is a very small sliver of light that is coming from in between the end of the pedal and the cage seat. They are not cracked or chipped though. Here is a picture of the inside of the cage facing the pedals with the most light visible.  IMG_2606.thumb.JPG.c3e8ef606cacb45999e2f3d83b69e815.JPG

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1 hour ago, Kinger317 said:

A engine needs to be airtight in order to Idle well, I'm sure you know this but you don't want to idle a bike indefinitely. I think mine would 10 months a year but in the peak of the summer it seems to idle good for 15 seconds or so then starts to drop. I don't worry about it, I think it's pretty normal. If you have the reed off make sure you seal it on all surfaces good when you reinstall it.

I am at 1300 feet 80° right now and I am very happy with 45 pilot, N3EW-3, 40 power jet, 175 Main. Your needle sounds very lean to me.

 

So looking at my reeds picture do I need new reeds and my jetting is lean to compensate a rich condition caused by bad reeds? 

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Never compensate the jetting for defective parts, like a band-aid on a broken arm.

As mentioned, VForce quality control is often questionable,

there must be 1-2 posts like this per month showing air gaps on brand new assemblies, with usage it's not going to get any better.

For you to decide but good reeds can make a noticeable difference in low rpms operation so personally I'd would not run those pictured.

 

Your user name suggest you trail ride your YZ250,

if so, perhaps the Yamalube 2R (a high flash point racing premix) mentioned in your first post is also a bit overkill for the usage.

Edited by mlatour

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42 minutes ago, mlatour said:

Never compensate the jetting for defective parts, like a band-aid on a broken arm.

As mentioned, VForce quality control is often questionable,

there must be 1-2 posts like this per month showing air gaps on brand new assemblies, with usage it's not going to get any better.

For you to decide but good reeds can make a noticeable difference in low rpms operation so personally I'd would not run those pictured.

 

Your user name suggest you trail ride your YZ250,

if so, perhaps the Yamalube 2R (a high flash point racing premix) mentioned in your first post is also a bit overkill for the usage.

I've never got this yz250 to run right since purchase, I bought it used and the mid range wouldn't let the bike wrap out. The guy had a 52 jet with a 182 main! Stock cylinder mind you, not a 300 kit. So I finally got it to run perfect in all ranges and this is where I end up with a bike that doesn't idle and runs great otherwise. Not trying to bandaid anything. Just want my bike to be right. I want to run oem reeds to eliminate this dang VF3 stuff. It's a lot of money from Yamaha though... like $300 a lot... I don't think too good of an oil is going to cause this symptom? 

Edited by YZ250TRAIL

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So looking at my reeds picture do I need new reeds and my jetting is lean to compensate a rich condition caused by bad reeds? 

I personally don't get too freaky about reeds, if they're thick and not cracked and close to sealing a little bit of light showing through doesn't bother me. I figure there fluttering all the time and when they're hit with pressure I would think they slam shut ok. I'm freaky about where the gasket surfaces seal.
I only commented about your jetting because of the needle clip position. Strikes me as lean especially with the 50 power jet. I go the opposite way with the rich needle clip position and leaner power jet, but I think I'm on an island with that too!
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No the choice of oil would not prevent your engine from idling, just be more prone to spooge/foul in lower combustion temps situations.

(also a common TT forum topic, using 'racing' oil in recreational applications or at lower than WOT motocross race speeds/rpms)

 

How fresh is your piston and rings?

Compression reading ?

Edited by mlatour

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Those reeds should sit flush, from my experience.  Worn reeds aren't always torn or chipped, but often not resting flat.  If they aren't shutting the whole way during the engine cycle then they aren't performing their entire job and you probably aren't getting the best compression.  They should be forced open only by engine vacuum and when that vacuum is released, should close completely.  Some of your engine compression is going toward shutting that gap on those reeds.    For the price of a set of reeds and given the time you have invested, it wouldn't be a waste to get new ones.  IMO those as pictured are done. 

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A engine needs to be airtight in order to Idle well, I'm sure you know this but you don't want to idle a bike indefinitely. I think mine would 10 months a year but in the peak of the summer it seems to idle good for 15 seconds or so then starts to drop. I don't worry about it, I think it's pretty normal. If you have the reed off make sure you seal it on all surfaces good when you reinstall it.
I am at 1300 feet 80° right now and I am very happy with 45 pilot, N3EW-3, 40 power jet, 175 Main. Your needle sounds very lean to me.
 

Ditto 45, 3rd clip JD red, 175 main. No PJ. I can't imagine running on 1st clip.

Sent from my SM-G935V using ThumperTalk mobile app

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25 minutes ago, mlatour said:

No the choice of oil would not prevent your engine from idling, just be more prone to spooge/foul in lower combustion temps situations.

(also a common TT forum topic, using 'racing' oil in recreational applications)

 

How fresh is your piston and rings?

Compression reading ?

Compression reading was 185psi about 5 hours of riding ago. I will do a re reading again and get back with you soon. 

Edited by YZ250TRAIL

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