Jump to content

2004 YZ125 bog at WFO


Recommended Posts

A few things to mention is jetting is good.. it revs fine in neutral or with the clutch in (no load) and it seems to rev OK in first.. 2nd and 3rd and probably 4th and 5th dont rev at all.. to me it seems like the choke is on.. but its not.. messing around i turned the choke on and it made it a little worse but barely. is it possible for the choke to break? I have never experienced this exact issue.. also the spark plug is dirty from use but not to the point that it should cause a problem like this..

Link to comment
Share on other sites

the bikes new to me... it has been running fine for the last 15 hours (approximately) just tonight it started doing it i noticed it exiting a berm and going through 2nd and 3rd and then i kinda fooled around for 5 minutes and it got worse... so its happened in the last 10-15 minutes of run time..

How did you know it was a big bore? I didnt mention that? For the reason that it was jetted for it and ran fine with it before

Link to comment
Share on other sites

the bikes new to me... it has been running fine for the last 15 hours (approximately) just tonight it started doing it i noticed it exiting a berm and going through 2nd and 3rd and then i kinda fooled around for 5 minutes and it got worse... so its happened in the last 10-15 minutes of run time..

How did you know it was a big bore? I didnt mention that? For the reason that it was jetted for it and ran fine with it before

it's in your signature wyatt

Link to comment
Share on other sites

Might be the clutch. Check your clutch cable, and if that isn't it you may need to check or replace the clutch itself.

how would the clutch effect this? Clutch seems to be good but i'll check it out.

move the needle up one. In other words, move the clip on the needle down one.

why would the needle effect upper rpm? I'll try it..

it's in your signature wyatt

😏 my bad

Link to comment
Share on other sites

Might be the clutch. Check your clutch cable, and if that isn't it you may need to check or replace the clutch itself.

How could the clutch contribute to a bog? If the clutch was going out it would rev even higher, right?

Link to comment
Share on other sites

Warm the bike up. Cruise slowing in 3rd gear on level ground. Roll on the throttle gradually. If it pulls clean without a ton of smoke or burbles or puking, it's not rich. Now slow down again. Still in 3rd and on level ground and cruising slowly, whack the throttle full open. If it transisions smoothly like the slow roll on, congrats. If it bogs (cut's out like it's off and then comes back), move the needle one step richer like I said earlier.

Link to comment
Share on other sites

Well I think i'll richen up the needle (move clip one notch down) because if i roll on pretty smooth it goes fine. but if i open it all the way from the get go it just sputters.. blah

Any possibility that means it's too rich?

Link to comment
Share on other sites

If nothing changed in those 15 hours then it's not a setting that needs to be adjusted IMO, something is broken or clogged.

Start with your compression, make sure that it is good. Bike cold, WOT, 4-5 kicks get average PSI. Should be 200+. anything lower than 180 something bit the dust at 15 hours and I'm going to guess it's a ring.

Pull the power valve cover, you need to remove the pipe to do this. remove the secondary port covers on both sides of the jug (two phillips screws each) and then remove the power valve actuating arm. Twist the shaft clockwise, there should be spring tension (slightly) until you hit the second stage in which the secondary valves will move. They should move with no binding, but it should still be a little hard to twist on the second stage where the big spring tension kicks in. If the valves are moving and nothing is binding then the powervalve is ruled out.

Pull the rear subframe and pull your carb, remove the reed cage boot and reed cage assembly. Check the reeds, there should be no cracks, or gaps, they should lie flat and seal.

Take off the float bowl and remove everything except for the TPS (need special screwdriver, plus it's set at factory and removing it screws the position). Clean out all the orifaces and use q-tips to remove any gunk. Clean all the vent lines, clean the vents themselves, they all lead to the top of the float bowl and should not be blocked. The left vents have a small detour to the float bowl and may look obstructed but they are not, just the way the mold is, the other side you should be able to see through to the bottom of the carb looking straight down.

Clean the main jet passageway, do not use brass or steel to do this, no pins or anything metal, use q-tips or toothpick etc.

Clean out the choke passageway while your at it.

Check float hieght, should be around 6mm and the valve should look nice and pointy. You can test the valve by adjusting the float to the proper hieght and blowing through the fuel line, no air should pass. Clean this area out if it does, the slightest piece of gunk will allow the valve not to seal, if it still does not seal and the height is correct then the valve is bad, replace.

Clean your air filter, water will cause the bike to run like crap if you've been going through it and it's still in the filter, trust me I know 😏 Also when your jetting is very precise a dirty filter will make the bike run like crap, at least it does with mine. With the stock jetting and needle this didn't seem to be an issue..

Finally clean the tank, remove the petcock and clean that guy out too, chunks of dirt, wood and bugs will slow the bike down bigtime 😏

These are all the things off the top of my head that could cause running issues that could have been broken/clogged since you rebuilt the bike.

Link to comment
Share on other sites

I ordered a new piston for it but its backordered.. I wasnt planning on riding it anyway till i got that in... Looks like I'll get it fresh and go from there... The float valve has been leaking like the float level is off or maybe the valve is just bad.. but now it doesnt seem to leak at all or as much... might just have something plugged up bad... going to tear the carb apart sometime today... if im bored I might start checking out the motor... I have plenty to do to freshen this bike up so back ordered parts arent the end of the world since I'll be busy and tired the next couple weeks anyway.I'll get back to you guys if I find something in the carb or motor... I wont know what will have it fixed till i get the new top end since i wont have it back together till then... I really hate to change a bunch of things at once because then its hard to know what actually fixed it..

Link to comment
Share on other sites

Well the engine is ruled out as the top end is in good shape and couldnt find anything wrong. (will be going back together freshly honed with a new piston and rings). the carb is clean and awaiting install. I couldnt find anything wrong with it or plugged up (but i cleaning it very well and tore it all apart so im sure i cleaned something out without knowing it. Haven't pulled the reed cage off yet but I might later tonight or eventually (i have a lot of time until the piston gets here). The air filter is dirty but not clogged up dirty.. just 5 hours of riding in mud and dust dirty... At this point. if it bogs when I put it back together I will be putting a different pipe on and then chase jetting issues....

Link to comment
Share on other sites

At this point. if it bogs when I put it back together I will be putting a different pipe on and then chase jetting issues....

If it still bogs, chase your jetting first. Your trying to do too many steps at once.

Link to comment
Share on other sites

no... because if I jet it with the current pipe I will have to chase jetting with the new one... its possible i dont want the other pipe and in that case i will just chase jetting with all the same variable:)

Cool, its just the 1st time you mentioned a diff. pipe. It just kinda seems like you'd rather throw new parts at the situation, rather than diagnose it.

Link to comment
Share on other sites

Cool, its just the 1st time you mentioned a diff. pipe. It just kinda seems like you'd rather throw new parts at the situation, rather than diagnose it.

oh I have the pro circut pipe already... I wouldnt be spending money on it... And chasing jetting is never fun so i rather only have to do that once.. but im thinking i wont use the pipe as i really liked the power curve how it is/was.... but no i wont be purchasing new "bling" parts to fix the situation.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

×
×
  • Create New...