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Cr125 bogging down

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So I've had my 99 cr125 for a couple weeks and I absolutely love it. The top end blew up the day after I got it and I had to rebuild it so I figured I would give it a carb clean while I had it apart and was waiting for parts. It already wasn't idling right. So it started first kick after the rebuild I just had to mess with the idle screw after but was running great. Problem with it is it's very hard taking off and still doesn't idle right.. I have to ride the clutch for a while taking off with it. Bogs quite a bit. Has tons of medium and top end power however though. Just taking off or barely moving.. Id also like to say that this bike is my first 2 stroke or even motocross bike so this could be completely normal for all I know haha. Also I'm running 35:1 and I noticed the throttle cable is rusted on one spot so it's probably stretched but still had plenty of pull when I took the carb off. I know there are probably 1000 different things that could be wrong with it but I'm just looking for some first opinions/ thoughts... My guess is adjusting the jetting. Thanks!

Edited by BarnacleBill

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When you say "bog", do you mean the bike misses pretty badly and starts cutting out when you gas it? Or is it just slow as crap until you get to the mid-top end range? 

 

125's generally don't have any bottom lug. It's like only having a turbo valve that kicks in from mid-top. Lotsa clutch feathering action. 

 

I thought mine was all fried and still running weird after a complete engine rebuild. Turned out I just had to ride it in the higher RPM's.

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So everyone has a different opinion on if two strokes will idle or not. My two stroke will idle all day long every day until it runs out of gas running on a 32:1 ratio. It will do it at a normal rpm too. In my opinion they should idle. As far as the bog many different things can be affecting the bike, like gearing, a dirty pilot that just didn't get cleaned well (those small holes can be difficult to get clean.) if you go to the carburetor and fuel injection section on this form there is an excellent write up on how to determine jet sizes and I would jet the bike according to that section. I would think that putting the power valve back together incorrectly could cause bog too in the lower rpms.

Good luck,

Chris

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It sounds like I'm trying to go from idle to wide every time I take off and I look like a dumbass. I don't really know how to explain it anymore, am I supposed to just have it screaming and dump the clutch every time i take off? It's basically impossible to take off if it's uphill at all. Like I said before this could normal I have no idea haha

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Like has been said, it could be power valve related, it could be jetting related.  I would start with the power valve, take the left side power valve cover off and rev up the bike, does it snap open and then shut, is the power valve closed before starting the bike?  If your power valve checks out, then post your jetting specs here along with your altitude and we can see if it is a jetting problem.  If your power valve isn't closing on idle, it will never have any low end. 

Edited by frdbtr

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So I messed with the jetting a bit and went off the honda manual and that didn't work. What is the power valve supposed to do? It is opening when I rev the bike but it doesn't seem to snap all the way back in.. Also now that I'm getting used to the bike I'm noticing it bogging more even in higher gears if I give it too much throttle. I'm at a loss.

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So I messed with the jetting a bit and went off the honda manual and that didn't work. What is the power valve supposed to do? It is opening when I rev the bike but it doesn't seem to snap all the way back in.. Also now that I'm getting used to the bike I'm noticing it bogging more even in higher gears if I give it too much throttle. I'm at a loss.

 

The power valve has to snap all the way shut in order for the bike to have any low end.  You are going to need to remove the pipe and take the valve cover off of both sides of the motor.  Once the valve covers are removed, you will see an allen screw attached to a spring, that is what makes the power valve spring shut.  you will need to loosen the allen screw on both sides, and then turn the rod that rotates the power valves open and closed until both are shut.  Then you will apply pressure on the spring before tightening the allen screw so there is a preload on it.  Make sure both sides are preloaded before putting it back together. 

Edited by frdbtr
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Okay yeah you have to push it back in with your finger after revving it. I have the bike stored somewhere else so I will try it tomorrow. I appreciate the help!

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Seems a lot better now. Still not perfect as far as acceleration but I'll play with the air screw a bit. I can actually shift going uphill now haha. Thanks for the help!

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If it still doesn't accelerate normally with just rolling on the throttle you still have something wrong.  Time to check the reeds to see if they have cracks or breaks.  You said you put a new piston in it when you bought it, did you use OEM or aftermarket (don't want to sound condescending but you probably want to check piston orientation, I have seen them put in backwards).  OEM piston has an "IN" mark that should be on the side of the reeds, aftermarket pistons usually have an arrow that is supposed to point in the direction of air flow (towards the exhaust).  Finally you want to make sure your silencer has fresh packing in it, which can affect performance if the packing is worn out.

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It's a wiseco and I'm positive it's in the right way, I checked when i took the pipe off. I'll get to the reeds and check out the silencer when I get a chance.

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Yeah, it is a 125 and most people will shrug off low end bogs as it just being a 125 and it is supposed to hot have any low end.  Well, that is true to a point, it should accelerate and progress through the RPM's like a normal 2 stroke would.  Good luck, the 99's have a good motor.  If you are looking to use this as a trail or play bike, I would highly recommend getting a 144cc bb kit with either low/mid porting or "Mo Betta" porting (from eric gorr). 

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Hey! So I finally got around to checking the reeds lol. I noticed one of the flaps has a couple small pieces chipped out of it and isn't closing all the way and you can see a little bit of light shining through it. I'm probably going to order new reeds, any suggestions? Mostly trail riding and pit riding. Wanna try out a track some day but not planning on racing this bike.. Thanks!

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Hey! So I finally got around to checking the reeds lol. I noticed one of the flaps has a couple small pieces chipped out of it and isn't closing all the way and you can see a little bit of light shining through it. I'm probably going to order new reeds, any suggestions? Mostly trail riding and pit riding. Wanna try out a track some day but not planning on racing this bike.. Thanks!

for OEM 1999 cr125 reeds partzilla has them pretty reasonable I think they are #6 on the parts list here:

http://www.partzilla.com/parts/search/Honda/Motorcycle/1999/CR125R+A/CRANKCASE/parts.html

NOTE: you must add quantity 2 to get both sides of reeds... A quantity of 1 will only get you one side of the reeds..

Edited by M3NT4L5

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Hey! So I finally got around to checking the reeds lol. I noticed one of the flaps has a couple small pieces chipped out of it and isn't closing all the way and you can see a little bit of light shining through it. I'm probably going to order new reeds, any suggestions? Mostly trail riding and pit riding. Wanna try out a track some day but not planning on racing this bike.. Thanks!

 

You can't go wrong with OEM reeds from partzilla.  If you want to try aftermarket, look into boyesen's carbon fiber petals for OEM replacements.  They may add a little extra throttle response. 

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Also quick tip for this bike I have a 96 Cr125r and I would not have the bike idle. You will go through lots of spark plugs and there will be a big load on the engine when you slow down and try hitting the gas again it’ll make you feel like you a riding a bull. You should have to keep the bike running yourself by twisting the throttle. Pro racer for motocross showed me this and this will let you have more control over the bike and less wear and tear in the engine. 

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