00 yz 125 jetting issue, bog problem

[dkgoodrich]

Ok so I have been reading a bunch on jetting my carb so I opened mine up to check the jets, they were all stock jets, needle was is 2 position instead of 3. So now I have a good start point.

The reason why I wanted to jet it is because if you go from no throttle and twist it back real fast, it bogs then screams. If you give it 1/4 throttle then twist it back, no bog, it just screams. I believe its a float level problem, but I have no float fuel level tool and am looking for one or looking to make one. I have messed with and set pilot screw and it doesn't seem to help the bog issue. Its set at 1 - 1/2 now.

I have put 33hr on my hour meter with this complete rebuild. I have also never seen a white.. or brown plug, mostly black.

My bike is STD bore and has a FMF fatty with a powercore II shorty silencer. I got on fmf's website but they do not have any jetting specs for a 00 yz 125.


Any help, suggestions or comments on this bog issue are more than welcome and greatly appreciated.
dk

 

[whenfoxforks-ruled]

33 hours on a '00 125 rebuild, complete? Your compression may be low, your bore may not be round, anymore. After you check the bore, and get a new top end, go over this: post #4, http://www.dirtrider.net/forums3/showthread.php?t=159938&highlight=spankys+jetting+guide. Check your reeds, change the silencer packing, and replace your float valve and seat. It WILL rip again! Really look at your manual for the suggested hours on parts, check them at that mark, and then adjust how long you personally can stretch it.

 

[dkgoodrich]

I spent 750 on the bottom and top end [new sleeve] 33 hr ago... why would the cylinder be out of round? It still has great compression and starts 1st kick. I plan'd on re ringing it, new reeds, jetting it and running it for another 15-20hr then replacing the piston and rings. I have heard soo many mixed opinions on how many hrs it should get.. I've even heard lifespans as short as 5hr a ring and 15hr a piston, all the way up to 35-40hr a ring, 60-80hr a piston. Most people I have ran into giving me advise about how many hrs it should get simply guess by the 'tanks of gas' ran though it and have never actually ran a hr meter on there bike.

I edited the orig post with needle settings and slide settings that are in the bike and whats in my manual.. Everything is so far off what my manual says that I fell like I might as well start with a unmolested carb or find someone else to verify what should be in it. I always thought it ran good till I bought a couple other bikes and rode them, specifically our ktm 125..

Also I have read every jetting link on this site, just before I got started wanted to see what it had in it and start with all stock stuff, now I'm a little confused and am curious why someone would have changed all this stuff so drastically.

Thanks for your time,
dk

 

[whenfoxforks-ruled]

Could be someone "ported and polished" the cylinder, scrap. Or, putting a sleeve in a 2 stroke is no easy task, easily botched. And I know of no respectable builder that even does this. They open it up and replate it. It does not alter the port timing. Sleeving needs a miracle to get the original porting specs on the money. And the liner will not dissipate heat like the original. Takes a different ring also. Show me 1 oem 125 mx race bike with a top end life over 20 hours, please? Not guy bs.

 

[dkgoodrich]

I have 3 125 mx race bikes in my garage, all of them have over 20hr every top end they have ever had from day one.

I will put a new top end in this bike and reeds before I ride it more, or jet it.. Its not worth the money to 'push' it on this bike. I still want to pin point the bog issue though.

One the carb/jetting issue my cd manual had 5 manuals for a 99-01 yz 125, 5 different carbs all with different jets needles ect.. So I finally matched up the right carb numbers and all of my jets and needles are factory except the had the needle in #2 instead of #3

This bog issue has been going on for a long time, so honestly I think its a float fuel level issue.. I'm looking to make a fuel level gauge or buy one.. or just bend the float little a time to see if it helps.

Could reeds be causing low end failure like this? I'll check and inspect them..

Any other ideas are greatly appreciated.
dk

 

[whenfoxforks-ruled]

Reeds and the silencer packing will slow response off bottom. A plugged air filter of course also. Them stupid cd manuals, most are nothing more than parts micro fiches, hate them. A clymers would be way better, and of course the oem shop manual. Even the owners manual should cover the carb. There is a site for yamaha manuals free. The float valve is a high wear item, replace it yearly. Clean the carb thoroughly, actually poking something completely through the passages and jets. Floats do not go out of adjustment by their selves. They need help, except for leaking. Some carbs have a tube coming out of the bowl, it can hit the floats if one is not careful. Or someone has fuel puking, the first thing they do is fiddle with the float. You can not just look at, or push the float up and watch the gas ebb, and say they are good to go. Maybe with a strong magnifier and good light, no, just replace the float valve and seat! Performing a leak down test is real important for bikes that pass the float valve. As long as you have good top and bottom end sealing, then its all in the carb jetting. Used carbs, look very carefully at the slide needle and seat, as the 3 rubber connectors to the carb. The jetting guide in post #2 is fairly accurate, and eaasy to follow. An online parts micro fiche will tell you the stock jetting specs, some state it, and some just list it first: NEEDLE STD
275-14116-J1-00 , JET,PILOT(#35) STD
4KM-14142-35-00 ,. What does your air screw setting at 1 1/2 tell you?

 

[KX Jim10]

Richen needle 1 clip.

 

[dkgoodrich]

The silencer packing is new, I re pack it often and I use those 'ready' air filters on all my bikes and change them all the time as well.

The only reason the pilot screw is were its at is because I'm just putting everthing carb wise back to stock and starting from there. I also put the needle 1 clip richer back to its stock setting in the middle on 3 from position 2.

I honestly think my problem lies in either the float height, to lean of a pilot or reeds. Its pretty cold out right now and I don't remember having this problem when it was warm.

I'm going to stop by my yamaha dealer and get a float fuel level gauge and some pilot jets to start but havent been able to do much because its wet and cold out side.

Thanks for your time, I will update with my findings. I searched and searched and a guy on a 125 went a little richer on the pilot and fixed this very similar problem but one of the jetting guides said improper fuel level in the bowl can cause similar effects as a lean pilot.

 

[whenfoxforks-ruled]

Thats all good. A low float height would lean the engine. If its still lean, go bigger on the pilot. More than 2 jet sizes and I would be looking for an air leak. Look at the plug, wet or dry? If your rich and not able to feel adjustments with the air screw, drop the pilot. If the air screw is still ineffective, its the float valve and seat are bad. The air screw will tell you, if you listen? Any decent jetting guide will tell you, start at the pilot circuit. Then the needle and main. Stock jetting and 32 degree weather, Kentucky is not that much above sea level, it should be pretty close. Colder weather usually means the engine will run leaner, and require richer jetting. A bog can be rich or lean, the plug will tell you, dry or wet. NORMALLY, when your jetting is close, looking at the plug will tell you the main, proper plug temperature, and timing. But, if its bad enough to be bogging, it will be real wet or dry. And, these symptoms could point to mechanical reasons also. Especially ratty reeds! Thats a rich condition by the way.

 

[dkgoodrich]

Thanks for your reply,

I rode it today, with all the carb settings back to stock, 3rd clip on needle and 1.5 on pilot screw. It cleaned up the mid range a whole lot and took some of the bog out of the low end. I first rode it with the air screw 1/2 turn out and it really didn't like that it was real 'notchy' getting up to full throttle. I ran out of time so I will continue later messing with the pilot screw and pilot jet. I'm pretty sure I'm on the right track, it sure is a whole lot more fun to ride now. I'll keep checking my plug when I do and slowly work my way to tweaking the main. I'll update with my findings.

dk