I'm assuming its the Carb?

[Badgadjit1]

Hey all. I've been racking my brain and wallet over this one for a couple weeks now. :bang: I have a 99 YZ250 and its loosing power in the high end. Its perfect low to mid but when i hold the throttle wide open it bogs a little and loses power.

Things I've tried:
-Rejet bigger and smaller mains, ultimately just put the carb all back to stock. (jets and Needle pos)
-replaced gaskets in carb
-replaced gaskets in exhaust
-repacked exhaust
-Checked case for leaks
-checked reeds
-checked the power valve on the head
-compression is at 180psi
-took carb completely apart and cleaned many times
-sealed my airbox to make sure there aren't any leaks


Bad things i noticed:
-Also when i turn my idle screw, the idle will not change (on this carb the choke knob doubles as the idle, pull up for choke, turn for idle).
-Plug is wet and has oil on it.


couple questions.
1.I took out my choke/idle knob and was wondering if theres supposed to be an O-ring or anything up inside the gold part at the end. I have a side shot of the part i'm talking about and then a shot looking into the area i'm talking about.

http://www.flickr.com/photos/34665747@N04/6025217031/
http://www.flickr.com/photos/34665747@N04/6025216991/


2.also on my fuel cut solenoid, is there supposed to be an o-ring on the tip? (it would be tiny)
http://www.flickr.com/photos/34665747@N04/6025771570/


the microfiche doesn't show these parts and the guy at the shop didn't know cause he didn't have any in stock.

tonight as my last idea i'm going to see if the carb is getting too much fuel. Its not overflowing but i just don't know what else to look at.


Thanks for any input, it is much appreciated.

 

[dirt bike dave]

Is the fuel cut out solenoid working? If it is like the one I had on a '97 CR250 carb, you should be able to test it by hooking and unhooking it to a 12 volt battery. It should 'click' when it gets the power.

To me, your symptoms sound like that solenoid is not working.

Only other thought is maybe your air filter is dirty/too heavily oiled, but it sounds like you do a good job maintaining the bike.

 

[Badgadjit1]

air filter is clean, i didn't even oil it up yet cause i'm just firing it up in the garage.

And yes, i do try to keep up on the maintenance. it blows my mind how far i go to maintain the bike and then you have people that don't care and never clean anything and they're bikes never have problems. haha. oh well. I will give that a shot tonight as well and post the results. Thanks for the suggestion.

Here's a pic of the bike.
http://www.flickr.com/photos/34665747@N04/6026192180/

 

[High Lord Gomer]

Nice looking bike!

I would tighten that chain, though.

According to this you do need an o-ring (part number 31):

http://www.servicehondapsn.com/fich...ry=Motorcycles&make=YAMAHA&year=1999&fveh=902

 

[Badgadjit1]

Thanks! That o-ring is the one that goes over the threads. The one i'm talking about in this pic:
http://www.flickr.com/photos/34665747@N04/6025771570/

goes on the very tip of it, if there is to be one. Small enough to go onto the tip of a pen.

 

[High Lord Gomer]

Did you click on the link I put in my previous post? It is Yamaha part number 4JT-14147-00-00. 81 cents from Service Honda.

 

[Badgadjit1]

Did you click on the link I put in my previous post? It is Yamaha part number 4JT-14147-00-00. 81 cents from Service Honda.

Yes, i replied. That's not the right O-Ring. That one goes over the threads. The one I am questioning is the tiny that would go on the tip.

 

[Badgadjit1]

Is the fuel cut out solenoid working? If it is like the one I had on a '97 CR250 carb, you should be able to test it by hooking and unhooking it to a 12 volt battery. It should 'click' when it gets the power.

To me, your symptoms sound like that solenoid is not working.

Only other thought is maybe your air filter is dirty/too heavily oiled, but it sounds like you do a good job maintaining the bike.

So I was finally able to check the solenoid. It clicks when I hook it up to a 12volt battery but then I have to wait a few seconds after I disconnect it before I can touch it again to make it click. If I touch it to quick it won't click. Almost like I have to let it discharge before it will click again.

One thing I did remember though. I've ridden before in the past without that even hooked up cause I forgot about it. I don't remember having problems, it was a long time ago.

 

[helio lucas]

i have one complete engine sitting in my garage, with carb.
later when i get home i will check if the carb has the tinny o´ring...

 

[Badgadjit1]

Thanks, I really appreciate it. Not sure if that would be the source of my problems but we'll see!

 

[whenfoxforks-ruled]

What changes have you made to the power jet? How is the exhaust valve working/set? The silencer core is intact and centered?

 

[helio lucas]

the tip of the solenoid has a rubber, not exactly a o´ring. you may have to eventually buy the entire solenoid though :nod:

my budies carb choke knob is different than yours, it doesn´t has the small rod but it has indeed the rubber (again, not exactly a o´ring)


please check your ignition while you are at it, may look fuelling problems but may be weak ignition. the service manual shows the proper procedure to check the ignition system. normally only involves coil static values, usually resistor (ohm scale with a multimeter)

:cool: :cool:

 

[helio lucas]

for what is worth he was running 55 slow jet and 175 main jet... i bet is stock.
i am in europe, so most likely the bikes have different specs.

 

[Badgadjit1]

What changes have you made to the power jet? How is the exhaust valve working/set? The silencer core is intact and centered?

I haven't made any adjustments to the power jet, other than taking it out and looking at it and making sure the ports are all clear.

Silencer isn't very old. it's an R304 Pro Circuit and it has been freshly repacked.

 

[Badgadjit1]

the tip of the solenoid has a rubber, not exactly a o´ring. you may have to eventually buy the entire solenoid though :nod:

my budies carb choke knob is different than yours, it doesn´t has the small rod but it has indeed the rubber (again, not exactly a o´ring)


please check your ignition while you are at it, may look fuelling problems but may be weak ignition. the service manual shows the proper procedure to check the ignition system. normally only involves coil static values, usually resistor (ohm scale with a multimeter)

:cool: :cool:

Thanks for looking into that for me.i'm just not sure if that missing piece of rubber would be giving me the problems i'm having. Unless the piece that i one had on there is not lodged in a port somewhere, but i cleaned it pretty good and all the carb spray seemed to come out fine.

 

[Badgadjit1]

i'll look in my manual tonight and see about checking the ignition.

 

[whenfoxforks-ruled]

If the core is not centered/cracked or moving, it will effect the top end bad. Off brand jets do not flow like oem. Even some oem can be different. Some do their own mods drilling jets. A clogged gas cap or vent tube? Triple check the float level, not all carbs measure the same method. When it does it, pull the choke on and see if it helps? No response from idle adjustment means the pilot is pretty far off, use the choke to tell.

 

[Badgadjit1]

If the core is not centered/cracked or moving, it will effect the top end bad. Off brand jets do not flow like oem. Even some oem can be different. Some do their own mods drilling jets. A clogged gas cap or vent tube? Triple check the float level, not all carbs measure the same method. When it does it, pull the choke on and see if it helps? No response from idle adjustment means the pilot is pretty far off, use the choke to tell.

What do you mean the "core"