CR125 bogs down low.

[gixxerjeff]

I've got a garage full of 4 strokes all of which I could write books on and one 2 stroke which I seem to know shockingly little about.
I believe my power valve (correct term?) is caked up with black spooge. The bike used to want to climb a slick wall but lately it's been demanding downshifts that simply aren't there. Slipping the clutch at red line only to whiskey throttle it over everything is no way to live.
Am I on the right track? It almost wants to feel like a fuel issue but I'm using known good fuel and it's getting worse.....and I know what the tip of my pipe looks like (shame).
Is it something I should/can remove and clean or should it be replaced?
I sprayed the Carnegie Thanksgiving Day mud off it and rolled it in to the garage but haven't touched it beyond that yet.
Waiting for some barf direction.
Thanks.

 

[Maddevill]

Power valves often get gunked up with carbon and spooge. Clean them and check for proper operation. Also, if you have a lot of hours on the bike it's probably time for new piston and rings.

 

[motomania2007]

Power valve cleaning and time to repack the exhaust. The 2 stroke packing can become oil soaked/caked and not flow very well.
Could also be time for piston rings/new piston.

 

[OaklandF4i]

What year CR125? Is it the mechanical or electric powervalve?

If its the mechanical power valve, the bike ran strong before, its jetted correctly, and is just now exhibiting the low power and bog, I wouldnt be focused on the powervalve caked with spooge. I've seen many completely caked that still function. Of course its easy to clean if you just want to check it off the possible list.

If its the electric activated one, Ive never owned or worked on the electric version.

If it were my bike and the mechanical, I would do a two stroke leakdown test (different than a four stroke tool and they are not interchangeable) along with compression test. I would suspect an engine getting long in the tooth ready for a new top end (compression test) or a leaking wet side side seal (leakdown test) causing your low power or bog.

Yes, it could be other things. But this is where I always start so you arent chasing your tail. These are the two very basic things your motor must have before looking at everything else. :thumbup

 

[ScottRNelson]

When my son was 13 I bought an RM125 for him to ride that had almost no low end power, but good power once you revved it up. It was a lot harder teaching him to ride and work a clutch with power like that.

I eventually tried adjusting the mechanical power valve and found that the moron who had owned it before me had adjusted it so far in one direction that it was always in the setting that it needed for high speed operation. After adjusting it correctly, that bike was much easier to ride.

You should at least open it up and see if it is functioning correctly as well as being adjusted properly. If that all looks good, then look into rings and all that other stuff.

 

[gixxerjeff]

You make good points CJ...thanks....and thanks Scott & MD.
It's a 1995, I've had it for a few years but have done absolutely nothing to it. It's been a perfect little motorcycle the entire time. I'm hoping it's just crying out for maintenance.
The history of the bike is pretty much unknown. It's probably not a bad idea to paint this situation with a broad brush.

 

[OaklandF4i]

You make good points CJ...thanks....and thanks Scott & MD.
It's a 1995, I've had it for a few years but have done absolutely nothing to it. It's been a perfect little motorcycle the entire time. I'm hoping it's just crying out for maintenance.
The history of the bike is pretty much unknown. It's probably not a bad idea to paint this situation with a broad brush.

So it has the mechanical power valve then. The valve in its natural state is sprung closed, which is the position for more torque and why i would lean to suspect something else. It is still possible its the or one of the issues and easy to check. That said, here is a really good thread explaining how to set up your powervalve. Clean and check to see it isnt broken, cracked, frozen open, or not fully closing. Mechanical power valves are pretty simple once you figure out how they actually work. When reading about your powervalve, keep in mind you have the mechanical HPP vs the electronic RC system. HPP in my mind being the better of the two. :thumbup

Jetting, carb, and broken, worn out, or cracked reeds can also affect its performance. But as its losing low end power recently, I would be suspecting lower compression and/or engine seal possibly beginning to go. Good time to start at the beginning. An hour of inspecting and testing (leakdown and compression) will provide a real good picture of your motors condition and eliminate potential problems. Foundation before the roof. :laughing

If you dont have a two stroke leak down tester or one you can borrow, they are pretty easy to make from readily available parts at Home Depot for under $50, lots of threads on DIY testers if you dont have the $$$$$$ for the motion pro tool. I made my own.

 

[gixxerjeff]

Lots of useful information here CJ.
Thank you!
I've got some stuff to chew on. I'm certain I'll be back for more advice. :thumbup

 

[Frame Maker]

Hey Jeff, As you know, my daughter's YZ was exhibiting similar dis-function as your CR. I just tore into it this weekend and was expecting to see the power valve linkage sticking.

What I discovered was the linkage had become completely un-functional at the valve. A set screw on the linkage shaft had backed completely out. An actuation pin on one side of the valve had also come out. And another screw that holds one the valve haves in place had come out. The net result was both sides of the valve were no longer attached to the linkage and could open and close at will.

I did some searching on youtube and discovered that the pins coming out is a common problem on YZs. I don't know how the valve is actuated on your CR, but I would suspect somewhere in the actuation linkage it may have come apart as mine did.

With the YZ, it required pulling the engine to get access the valve assembly, but I now have peace of mind knowing what was causing the erratic power.

With the bike halfway disassembled now, I'll probably use the opportunity to install fresh swingarm bearings and replace some damaged bodywork. I hope to have the bike back together in time to ride Christmas morning with my daughter. Hope you get your bike resolved and can join us. :ride

 

[gixxerjeff]

Thanks Julian. Good info.
....and yes, we were experiencing similar bummers.
Sadly, mine were even further exposed by some shitty riding.
I'm gonna dig in to it this weekend.
I had fun riding with you on Thanksgiving. :thumbup

 

[elskipador]

i had a 96 for a while & it was pretty trouble free. i wouldn't worry about the power valve being covered in black gunk, they get like that within a few hours of riding. its a 2-stoke, you're burning oil & its in the exhaust track. i'd start with the simple things 1st. 1.) plug. 2.) exhaust packing 3.) inspect the power valve & make sure all the parts are hooked up & the parts in the exhaust tract can be moved with a little push from your finger. this power valves uses a centrifugal clutch so there isn't really "timing" for it. 4.) inspect pilot jet & fuel/air screw.