Hi everyone,
I have recently bought a Honda CR 125 year 1998 and from the very beginning faced some serious problem. To start with, I bought this bike on Ebay . I was told that this bike was parked in a garage for a year or so before I bought it. I bought it not running. I didn’t know the condition of engine so before trying to start it I did a few things: put a new air filter, thoroughly cleaned the carb and all jets, put a new spark plug, took out the engine and rebuilt the top end with OEM Honda piston kit, filled tank with fresh fuel, filled gearbox with fresh oil.
A few more remarks:
1)I found a lot of dirt when took off the flywheel cover for the first time.
2)I didn’t change the head gasket when rebuilding top end. It looked absolutely perfect.
3)I haven’t had an MX before so I can’t compare, but the kickstarter moves really easy, I can move it all the way with my bare hand quite easily. Today I will ask one mechanic to test compression.
4)Many times checked throttle cable, it is not sticking anywhere.
5)Reassembled carb for second time, jets are clean, bowls moving freely.
6)Rubber boot between carb and cylinder has no cracks in it.
And the problem is:
When assembled everything back, I had to kick it about 30 times to start it and when it started, the idle RPMs went sky high at once and never dropped, it was shattering and running full throttle. A lot of white smoke came from exhaust can and exhaust manifold was covered in black oil. It’s quite hard to tell, but it seems to be like gearbox oil rather than premix. I use Motul fully synthetic premix oil and it has some nice smell. I shut it off after a few seconds and tried to start it again. Now it started from the first kick but sky high RPMs and smoke was here again. I tried to adjust idle RPMs on the carb in all possible ways and it made no difference. Some fuel spilled on the ground from carb vent hose.
Here is a video of my problem with two photos in the end of video: in youtube search field paste " Honda CR 125 1998 sky high idle. How to solve it? " and choose the first video, length 41 second. It doesn't allow me to post a link.
As I understand, the problem is probably an air leak. I didn’t change a topend gasket when rebuilding topend but it seems to be perfect. I changed the cylinder base gasket, torqued evertything really well, base gasket looks absolutely dry so visually it is not leaking. It could be crankshaft seal at the flywheel side. I put on flywheel cover with fresh rubber gasket and some sealer and I think that very little air could be sucked through this cover and crankshaft seal to the inside of engine. Could it cause such high RPMs?
All in all, two short questions:
1)What could cause such sky high RPMs with no throttle?
2)It was a new piston kit, so it went almost full throttle and probably with lean fuel mix with no break in. I started my bike about 8 times for not more than 10 seconds. Will I have to rebuild the top end with new parts or will this piston be still usable?
This is my first MX, so I would really appreciate your help :nod:
ISSUE SOLVED!:
Ok, I feel quite silly now. It turned out to be throttle cable at fault. I don't know how could that happen, but throttle cable was too short. I adjusted both cable adjusters all the way in to loosen the cable and it was still too tight. The slide in the carb never closed. I thought that the slide must be open a bit but it turns out that it must be fully closed. I disconnected the cable at the throttle tube, the slide fully closed and now the bike starts easily and doesn't rev by itself.
Next issue - smoking. I took off right side cover and found that the right crank seal has jumped out of it's place. So now I want to replace it. However, manual says to fit it as deep as was the old seal. But as the old seal is out of it's place, I don't know hoe deep should I seat it. Does it have to be flat with the case surface or does it have to go deeper? How could I find out that?
Also, manual says only to grease the inner perimeter of the seal on right side crank seal, and on the left side, it says to oil the outer perimeter and to grease the inner. Why is there a difference? I believe that the outside perimeter should be left clean in order to sit it tight in the place.
And thank you everyone for the help :)
I have recently bought a Honda CR 125 year 1998 and from the very beginning faced some serious problem. To start with, I bought this bike on Ebay . I was told that this bike was parked in a garage for a year or so before I bought it. I bought it not running. I didn’t know the condition of engine so before trying to start it I did a few things: put a new air filter, thoroughly cleaned the carb and all jets, put a new spark plug, took out the engine and rebuilt the top end with OEM Honda piston kit, filled tank with fresh fuel, filled gearbox with fresh oil.
A few more remarks:
1)I found a lot of dirt when took off the flywheel cover for the first time.
2)I didn’t change the head gasket when rebuilding top end. It looked absolutely perfect.
3)I haven’t had an MX before so I can’t compare, but the kickstarter moves really easy, I can move it all the way with my bare hand quite easily. Today I will ask one mechanic to test compression.
4)Many times checked throttle cable, it is not sticking anywhere.
5)Reassembled carb for second time, jets are clean, bowls moving freely.
6)Rubber boot between carb and cylinder has no cracks in it.
And the problem is:
When assembled everything back, I had to kick it about 30 times to start it and when it started, the idle RPMs went sky high at once and never dropped, it was shattering and running full throttle. A lot of white smoke came from exhaust can and exhaust manifold was covered in black oil. It’s quite hard to tell, but it seems to be like gearbox oil rather than premix. I use Motul fully synthetic premix oil and it has some nice smell. I shut it off after a few seconds and tried to start it again. Now it started from the first kick but sky high RPMs and smoke was here again. I tried to adjust idle RPMs on the carb in all possible ways and it made no difference. Some fuel spilled on the ground from carb vent hose.
Here is a video of my problem with two photos in the end of video: in youtube search field paste " Honda CR 125 1998 sky high idle. How to solve it? " and choose the first video, length 41 second. It doesn't allow me to post a link.
As I understand, the problem is probably an air leak. I didn’t change a topend gasket when rebuilding topend but it seems to be perfect. I changed the cylinder base gasket, torqued evertything really well, base gasket looks absolutely dry so visually it is not leaking. It could be crankshaft seal at the flywheel side. I put on flywheel cover with fresh rubber gasket and some sealer and I think that very little air could be sucked through this cover and crankshaft seal to the inside of engine. Could it cause such high RPMs?
All in all, two short questions:
1)What could cause such sky high RPMs with no throttle?
2)It was a new piston kit, so it went almost full throttle and probably with lean fuel mix with no break in. I started my bike about 8 times for not more than 10 seconds. Will I have to rebuild the top end with new parts or will this piston be still usable?
This is my first MX, so I would really appreciate your help :nod:
ISSUE SOLVED!:
Ok, I feel quite silly now. It turned out to be throttle cable at fault. I don't know how could that happen, but throttle cable was too short. I adjusted both cable adjusters all the way in to loosen the cable and it was still too tight. The slide in the carb never closed. I thought that the slide must be open a bit but it turns out that it must be fully closed. I disconnected the cable at the throttle tube, the slide fully closed and now the bike starts easily and doesn't rev by itself.
Next issue - smoking. I took off right side cover and found that the right crank seal has jumped out of it's place. So now I want to replace it. However, manual says to fit it as deep as was the old seal. But as the old seal is out of it's place, I don't know hoe deep should I seat it. Does it have to be flat with the case surface or does it have to go deeper? How could I find out that?
Also, manual says only to grease the inner perimeter of the seal on right side crank seal, and on the left side, it says to oil the outer perimeter and to grease the inner. Why is there a difference? I believe that the outside perimeter should be left clean in order to sit it tight in the place.
And thank you everyone for the help :)
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