New to Motocross, need a few things cleared up

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Mattmurphy22

Member
Mar 22, 2010
11
0
Hey guys, so i've had a bike for a couple of months now, it's an rm125 2000 year. First couple of problems i've had is it takes quite a while to start the bike, i'm not sure if this is to do with the spark plug or something, but i'm in the process of getting a new one. Another thing is there is quite a lot of smoke coming from the silencer, which I know isn't the fuel ratio, and there is what i've heard, unburnt 2 stroke oil dripping from the connections between the header pipe and the silencer, which is a bitch to clear up.

-The last major problem I had was a couple of days ago, i was riding in a very muddy field and i switched up a gear, the bike started revving a lot and wasn't moving. I then pulled the killswitch and it was still going, then the engine started smoking! i eventually had to purposefully stall it. Anyone know what the problem would be?

-And finally, I want a full engine rebuild, absolutely EVERYTHING, does anyone know a rough estimate of how much it would cost?

Thanks, matt.
 
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julien_d

Member
Oct 28, 2008
1,788
1
rebuilding bottom and top at a shop is looking at around $1,000, maybe a good deal more or maybe a bit less depending on what needs to be done. You'll have to call around to get more accurate quotes in your area.

Sounds like you have jetting issues or problems with the carb. I'd pull the carb apart, clean the jets, take note of what jetting it has installed, etc.
 
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julien_d

Member
Oct 28, 2008
1,788
1
Carb is in between the airbox and the engine. Loosen the clamps on the rubber boots on either side and pull the carb out. Remove the 4 screws on the bottom and that will give you access to the jets. Basically just take apart everything you can, clean it all as well as you can, and put it back together. There are two brass jets that will have numbers stamped on them. Take note of those numbers, and then order some jets that are one or two sizes smaller than what you have now.

Purchase a shop manual! You can save about 50% on the rebuild cost if you do the work yourself.
 
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Mattmurphy22

Member
Mar 22, 2010
11
0
Okay thankyou! Wil this cover the issue i had when my engine started smoking and the smoke from the silencer?
 
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speedy1

Member
Jul 21, 2009
42
0
It's a 2 stroke, it will smoke some. They burn oil with the gas as they run for lubrication. The richer the mixture, the more smoke you will get. Rich jetting can also cause this. It's possible you need rings, but two strokes do smoke some.

The exhaust spooge you are getting at the joints is normal. Again, more with a richer mixture. I have also heard that if you get spooge dripping out of your silencer, the packing material in the silencer is likely saturated and needs to be replaced. This may also be the reason for the spooge at the joints.

Likely, when you went up a gear, you actually only went up halfway and went into neutral. That is why it was revving and not moving. Push it down again to get it back into gear. If you were riding in mud and water, likely it was steaming off the exhaust and engine because you were revving the crap out of it and it was hot :)

The kill switch issue might be a problem though. You need to hold it down until the engine dies. If this doesn't work, you should get it fixed. It would suck not to have that if there is a problem while you are riding.

Hard starting... Do you know how to use the choke on the carburetor? If no, it really helps to get the bike going when cold. Apply the choke, kick til it fires up, then turn it off and let it warm up a bit before riding.

It's just a lack of knowledge/experience with machines. Once you do this for a while and ask enough questions, you will get a better feel for what is normal and what is not. It takes a bit of time. You can change the plug if you like, that may help, but if it does fire up and run, the plug is working.

I hope this helps (as a start).
 
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speedy1

Member
Jul 21, 2009
42
0
one more thing, if you are getting white smoke (steam from your exhaust) and a lot of it, you could have a coolant leak that is allowing water into the engine as it runs. It would be a lot of white smoke though. lots. and smell like coolant instead of burning two stroke oil. That could be a head or base gasket, possibly a water pump seal, but not sure if there is a way to get into the engine through the water pump seal or. more likely the first two possibilities
 
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Mattmurphy22

Member
Mar 22, 2010
11
0
Ah guys thanks so much for the help. i'm getting a video off my phone from the other day in the muddy field. So i can show how much smoke i'm getting. Also sometimes when i come to stop i pull the clutch in it starts revving itself..?
 
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Mattmurphy22

Member
Mar 22, 2010
11
0
Ok guys can you add me on msn or give me your email so i can send you the picture of how much smoke there is? won't let me post a link here :/
 
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speedy1

Member
Jul 21, 2009
42
0
Are you sure the throttle is all the way closed (twist turned all the way forward) when it does this? I had an 88 CR 125 that had a sticky throttle. if you turned it halfway and took your hand off, it would stay righ there and wouldn't return unless you turned it closed.

Probably not that, but a possibility.
 
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speedy1

Member
Jul 21, 2009
42
0
I had to correct my e-mail. I must have missed the l after the underscore. Sorry. If you already send it, please resend.
 
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speedy1

Member
Jul 21, 2009
42
0
You can pull apart your twist throttle assembly. It's only a couple of screws and it comes apart. Disassemble it (disconnect the cable, and remove the throttle tube & clean everything. Blow it out with compressed air. You might try lubing things with dry graphite. If the cable itself is sticking, you should lube it and check for kinks or fraying. If you see those things replace it.

Another possibility is that your carb is just gummed up. Then you would just remove it, disassemble and clean it. This might be a good idea anyway. There isn't much to it. but you have to be patient and have some basic hand tools. Carb cleaner and compressed air is also needed.
 
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speedy1

Member
Jul 21, 2009
42
0
Does it clear up when it warms up? What are you running for a mixture? What kind of oil?

Do you notice that your coolant level is dropping? or if you take the pressure cap off (when cold) and start it up, do you see bubles in your radiator? This would indicate a coolant leak into the engine at some point. If it is still running pretty decent, I would suspect a head gasket if you notice any of these things.

-Wes
 
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speedy1

Member
Jul 21, 2009
42
0
Never heard back from you. Were you able to check any of the things I mentioned?

Does anyone else have any ideas?
 
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Mattmurphy22

Member
Mar 22, 2010
11
0
oh sorry, it kind of clears up but when i start to rev there's just as much smoke i reckon. I'm running 32:1 with MX7 oil. And i haven't managed to check because i'm at my dads and the bikes at my mums :) thankyou
 
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speedy1

Member
Jul 21, 2009
42
0
I hate to say this as some would disagree... but 32:1 is a pretty rich mix with stock jetting. I ran 40:1 pre-mix in my 1988 CR 125 (stock) and also in my 1996 KDX 200 (stock) and never had any issues.

If you have stock jetting set for your elevation and are not riding in cold temperatures, you should be able to pull off 40:1 with no issues. That might help clear up the smoke some and the exhaust spooge as well.

I would definitely check your coolant level before your next ride though and if it is low, top it up with coolant and start the bike with the cap off of the radiator. Then use a flashlight and look into the radiator as it runs and look for bubbles. If you see them, you need to check out your gaskets and cylinder for coolant leaks.

The smoke in the pic is pretty white and thick. It could just be your rich mix, but I would check the coolant out just as a precaution.

-Wes
 
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Mattmurphy22

Member
Mar 22, 2010
11
0
Okay. I'll get some pictures of the bike being revved at 40:1 and send them to you tomorrow :) thanks so much for the help speedy, i appreciate it all.
 
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speedy1

Member
Jul 21, 2009
42
0
Also... in regards to running a leaner mixture. Before doing this...

You should know what you have for jets and carb settings before messing around with it. Find out what the stock jet sizes should be, stock air screw setting and stock needle clip position and make sure your bike is there for your elevation.

If you go lean on the fuel/oil mix and and you have leaner jets installed, lean needle clip position or air screw setting it can cause a lean condition in your engine and burn it up.

Odds are it is stock and 40:1 will be just fine, but you never know. People mess with lots of things without knowing what they are doing :) I don't want to tell you something that causes you problems.
 
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Dirtjunkie85

Member
Mar 2, 2010
222
0
The thing I would be the most concerned about is if the throttle is sticking. Cleaning the carb, throttle housing, and throttle tube may do the trick, but you will also want to make sure the throttle cable is working properly. A new cable isn't terribly expensive. I had a nasty crash due to a stuck throttle so I am overly cautious about all of this. Your throttle should be really easy to pull and it should snap back crisp and clean.
 
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speedy1

Member
Jul 21, 2009
42
0
I second the motion on the throttle sticking. The suggestions I made are possible problems, but as you say, the cable itself could be the culprit. Might need to be lubed or replaced altogether.
 
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