Cr125 bogs at full throttle

[Brayden Stringer]

I think I have found the culprit to my 125 bogging problem. I had when trough everything on the bike I re-jeted the bike, adjusted float height, cleaned the air box and filter, changed the spark plug, cleaned the clutches, and even ran racing fuel through it ,but it seemed as though nothing would work. I called 5 bike shops and none of the things they suggested helped. But today I had taken the exhaust off because it was the only thing I hadn’t looked at ,the bike had been sitting for a while before I got it ,like 2 years, so I think this is the culprit. It is a fmf gold series expansion chamber so I’m not sure if the wire like stuff inside of it should be there or  not it is restrictive as I blow through it. The thing in the picture is what is in the pipe like right at the end of the expansion chamber

 

[Brayden Stringer]

And I’m pretty sure that when I pulled the spark plug it was a little bit lean but nothing to really make it bog like that and also all the exhaust fumes seem to be coming out around the exhaust manifold 

Edited July 21, 2019 by Brayden Stringer

[DesertCR]

I am currently restoring a 95 CR125 and I hope I don't run into this again as I had a similar problem with a previous bike and I ended up parting it out. Keep us updated, hopefully this is the problem and it runs right.

[_MountainRider_]

Uh no nothing should be in the expansion chamber. Make sure you clean it out thoroughly and repack the silencer. If it persist make sure powervalves are operation properly at high rpm. To do that pull off the cover and make sure it opens and closes smoothly while it’s running through rpms. If your reeds are worn they can fail at higher rpms and cause a bog. I’d try new pedals or if you go the “better” route I’d buy a boyesen reed cage. And if the issue somehow persists after everything above has been probably checked and done and YOU ARE ABSOLUTELY POSITIVE TOP END AND BOTTOM END ARE HEALTHY. I’d check and clean electrical and test everything you can with a multimeter and make sure everything is persistent

[Brayden Stringer]

I think the old owner had put an older jug on the bike when he rebuilt the top end so   I think that the bike does have the power valve but he did put a spring on the linkage to hold it down I think I have a picture of it if I don’t know if that would cause a problem tough 

[_MountainRider_]

I think the old owner had put an older jug on the bike when he rebuilt the top end so   I think that the bike does have the power valve but he did put a spring on the linkage to hold it down I think I have a picture of it if I don’t know if that would cause a problem tough 

That’s what is causing your problem. No powervalve=no high rpm power. Unless it’s built for it like a yz85 but the engine design is different. Basically the bike can not “open up” in high rpm. The valves work by increasing pressure and exhaust flow which in return sucks in more gas and air. That increases the rpms/combustion and Making more power. Basically no powervalve=no fun go go

[Brayden Stringer]

Now that I unclogged the rats nest that was in the exhaust pipe  the bike is up in your face the entire ride very fun ride  now I’m not sure if that valve thing is going to effect the longevity of the bike or what

[1stSSPZ]

When I found something similar in an older bike exhaust, mice had built a nest in it!

[mlatour]

About the spring holding the power valve linkage, you'll have to look into that and restore it to stock configuration.

 

Powervalves change the port timing, duration and area.

 

If the valves are held in the closed position = normal low-to-mid but no top end power

If the valves are held in the open position = no low-to-mid power but normal top end.

 

 

[Brayden Stringer]

5 minutes ago, mlatour said:

About the spring holding the power valve linkage, you'll have to look into that and restore it to stock configuration.

 

Powervalves change the port timing, duration and area.

 

If the valves are held in the closed position = normal low-to-mid but no top end power

If the valves are held in the open position = no low-to-mid power but normal top end.

 

 

Thanks I’m going to have to do that sometime so thanks for the help

 

[Orange Crush 500]

Looked like steel wool in ther to me.

[nino]

Oh Boy!

That's a older ATC-style cylinder (87-89) where they simply put a plug where you usually have the valve sitting and they fixed the rod coming up from the governor...i can't believe someone would do this!!!!

 

The ATAC cylinder usually has a round valve that is only working by changing exhaust volume. For better low-end it has the additional chamber up front on the cylinder added (more exhaust volume) and at higher RPMs it closes to have better high-end. So without the ATAC system attached i guess you have basically no low-end. Your top-end obviously is lacking because of that steel-weel plug you have in the exhaust...that doesn't belong in there!

 

But anyway - have your ATAC attached! On a twostroke any exhaust system helps to have a little more ponies....although on the ATAC system the gains are rather minimal which might have been the reason for the previous owner to have it eliminated altogheter. But the metal cover you have there won't hinder dirt/water from entering the bottom of your engine...that's NO GOOD !!!

Edited July 24, 2019 by nino

[nino]

This is how it's supposed to look like. There is a COVER over all this mechanism though which seals everything.Not just some metal sheet as on your bike....when dirt and water enters there...sooner or later your engine will fail!

Here's all ther parts of the ATAC system (which on your bike got basically completely eliminated)

The ATAC exhaust chamber. That's the volume which gets added for more low-end. As you can see i even added an additional spacer to add some more volume to it to help low-end some more.

 

[BV's]

does it make like a "booooowaaah" sound?  

[Brayden Stringer]

I have taken the spring off and it made no difference of top end or lower end it still rips hard it sounds good and feels like it has a lot of power

[Brayden Stringer]

9 hours ago, nino said:

This is how it's supposed to look like. There is a COVER over all this mechanism though which seals everything.Not just some metal sheet as on your bike....when dirt and water enters there...sooner or later your engine will fail!

Here's all ther parts of the ATAC system (which on your bike got basically completely eliminated)

The ATAC exhaust chamber. That's the volume which gets added for more low-end. As you can see i even added an additional spacer to add some more volume to it to help low-end some more.

 

Also I guess the old owner decided to put a lot of sealer or gasket maker or whatever it is down in the slot of the metal sheet so oil doesn’t fly out or water doesn’t go in 

[Brayden Stringer]

But there is water in the oil but i think that is because the oil seal failed on the water pump like I said the bike was sitting for some time

[Brayden Stringer]

I just crashed my bike so I guess I’m just going to sell it early and not run the risk of killing myself thanks for all the help everyone 

[Orange Crush 500]

Stop being a pussy Brayden, thats part of the game.?  Sometimes.your gona crash. Sometimes your gona get hurt. Everone on this forum has gotten hurt on there dirtbike, Many times..  Suck it , buttercup?

Get back on the bike, and take your time and learn to ride. Get the proper equiptment to save you from getting hurt like you did. The thrills are worth the pain..

I bet you didnt have riding boots on, did you? because if you did your shin would be fine, and would not of got hurt, and you would still be riding the bike.?

Go get some riding boots and get back on that bitch Stringer?

Edited July 24, 2019 by Orange Crush 500

[Brayden Stringer]

1 hour ago, Orange Crush 500 said:

Stop being a pussy Brayden, thats part of the game.?  Sometimes.your gona crash. Sometimes your gona get hurt. Everone on this forum has gotten hurt on there dirtbike, Many times..  Suck it , buttercup?

Get back on the bike, and take your time and learn to ride. Get the proper equiptment to save you from getting hurt like you did. The thrills are worth the pain..

I bet you didnt have riding boots on, did you? because if you did your shin would be fine, and would not of got hurt, and you would still be riding the bike.?

Go get some riding boots and get back on that bitch Stringer?

I don’t think I’m going to sell the bike it was like a in the moment thing like how can I ever give up riding it’s so fun