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2004 Honda CR125 - 2-stroke learning experience, but would like guidance for troubleshooting.

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Please bear with me, this is a detailed description of the events with all the background information I could give.

 

Note that I offer a 100$ bounty (in Bitcoins) for who ever help me diagnose and find the root cause.

 

Bought my first 2 stroke: a 2004 Honda CR 125. Previous owner ran it on 1:40 mix, with BR8EG NKG plugs as opposed to OEM recommendation which is 1:32 and BR9EG. Got a fair price as it came with “something broke” with the engine.  I took it apart with my father: top end is in great shape, but we found out it needed a new crank bearing. So we split the case open, replaced the bearing and the seals. We put it all back together and the bike started with about 10 cranks! But Note: there’s kind of a lot of oil (black) running down the exhaust port(header). My father says it’s normal for 2 strokes, but I have no idea.

 

So I drove it home on the back roads. About 10 minutes in, I enter a turn from 5th gear, downshift into 3rd, let the clutch go to slow down … the bike slowly dies off – and it wouldn’t start again. I pushed it up a long hill, ran it down and started it again on compression. I manage to get home, before I shut it down and kick started it again with no problem a few time.

 

The next day, we’re getting ready for a small ride. About to take off (after driving 5 minutes around the farm), the bike bogs down again and dies – and it wouldn’t start once again. My brother tried to pull me with his 3-wheeler, couldn’t get it to fire up on compression and I probably flooded the cylinder/plug while at it.

 

I was almost out of fuel (1:40) anyway. So on the 3rd day I bought and mixed 16l of regular fuel with 500ml of Motomaster 2-stroke oil(crappy tire) so 32:1. Also bought a bunch of BR8ES / BR9ES NGK spark plugs. I got home and took old plug out: it was wet and black. Then I checked the compression which was at 160~165. I took the compression gauge off before giving it a few crank (without a plug), didn’t spit any fuel. Last but not least I put one of my brand new BR9ES plug in. It fired up first kick start! So I shut it down, filled the tank with my new fuel mix, put my helmet on and I went for a very short ride (800m). JUST AS I was pulling back into my driveway, the bike dies again…

 

It hasn’t started ever since. I’ve tried a couple of new plugs, tried compression start.

 

A few things that bothers me, but I don’t know where I should begin.

 

  1. The black leak/oil running down the header
  2. Cheap fuel mix maybe? Should I try a premium fuel with some fancy oil?
  3. Should I try ES plugs instead of EG? Even thought I red it shouldn’t be a problem, just easier to foul.
  4. Maybe the carb is clogged/needs a cleaning?

 

Thanks!

Edited by Lemayilleur

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1. Usually a sign of overly rich jetting OR RIGHT crank seal is leaking trans fluid into engine causing your fouling.....I would check the jets (they have numbers on them ) and see what's in there....I suggest going to the stock sizes.

2. I don't think that is your problem BUT...... Most MX two stokes require premium gas (to prevent detonation) and two stroke oil that is made for watercooled MX bikes.

3. The EG plug will resist fouling better.

4. Yes that is a good idea.....check the float level too.

Edited by RBI

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Factory jet sizes for your 2004 CR125  are 420 main jet, 40 pilot jet, 2 turns out from bottom on air screw, and needle in the 3rd clip position. What is your elevation?

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2. I don't think that is your problem BUT...... Most MX two stokes require premium gas (to prevent detonation) and two stroke oil that is made for watercooled MX bikes.

 

Where would you begin? I mean, the fact that it ran with a new plug, but not for long makes me thinkg it it burned through the old mix (left over in the carb) for that 800m, then came the new mix.

 

But then again, my father said like you; it should at least run no matter the fuel/mix quality.

 

 

Factory jet sizes for your 2004 CR125  are 420 main jet, 40 pilot jet, 2 turns out from bottom on air screw, and needle in the 3rd clip position. What is your elevation?

 

As far as I know we are pretty close to sea level. (Gatineau, Quebec, Canada).

Edited by Lemayilleur

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I would get into that carb and check to see what jets are in the bike first. If it had old gas in it, it might need a cleaning anyway.

 

Then I would check the float level. Here is a good article....http://www.allthingsmoto.com/forums/f-15/how-set-your-motorcycle-carburetor-float-level-more-commentary-13608/  I do not know what level you are supposed to be at, sorry.

 

I would also pressure test (not compression)  the bike as it is a good way to rule out leaks that could mask other problems (read the "pressure testing a two stroke" thread pinned at the top of this forum)

 

Good luck! and have fun with it! Glad to see you are willing to get this done by your own hands and mind.

Edited by RBI

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old gas or new gas, what jets are in the carb will mostly determine if the bike runs rich or lean or just right.

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So, after checking and cleaning the carb. Found out some weird jetting and needle settings. I'll post what it was and what it is now (I'll update tonight), but it was weirdly configured. The jetting weren't following the vendor table at all.

 

Did a second compression check. It was only at 50 *cough*. We removed the top end and found out my piston/cylinder went to shit. Looks like it was grinding on the exhaust post side. The wring stuck to the piston on that side, and there's even a chuck on metal missing where the exhaust port splits in half. I'll have pictures tonight. Maybe you guys can diagnose what went wrong or if it was just a bad luck...

 

Rough times! :(

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Where would you begin? I mean, the fact that it ran with a new plug, but not for long makes me thinkg it it burned through the old mix (left over in the carb) for that 800m, then came the new mix.

But then again, my father said like you; it should at least run no matter the fuel/mix quality.

As far as I know we are pretty close to sea level. (Gatineau, Quebec, Canada).

Small world, you are from Gatineau!? Im in Aylmer! Got your service manual for your bike by any chance? You could test your ignition electricals. Ive encountered issues that when the bike warms up, the electrical component would fail.

Just saw your other post, did you have a wiseco pison that wasn't drilled by any chance? Some pistons need to be drilled to relieve pressure when you have a bridge in your exhaust port.

Edited by frank2014

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Small world, you are from Gatineau!? Im in Aylmer! Got your service manual for your bike by any chance? You could test your ignition electricals. Ive encountered issues that when the bike warms up, the electrical component would fail

 

Small world indeed! I'm actually located close to Gatineau, in Val-des-monts. We bought a digital PDF service manuals for my CR125 and my brother's YZ 125 - send me a PM :)

 

Spark seemed good. I believe I found much bigger issues :/. You'll see for yourself tonight when I post the pictures.

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Good to see you are finding the issues....the worst is when you have no idea what is causing the problem!

 

By the way...On that bounty, I don't think anyone here would accept that. We all love to ride, and love to help others get riding!! :ride:

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Just saw your other post, did you have a wiseco pison that wasn't drilled by any chance? Some pistons need to be drilled to relieve pressure when you have a bridge in your exhaust port.

 

What does the drilling look like? We'll be able to tell anyway, I'll have pictures uploaded tonight.

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What does the drilling look like? We'll be able to tell anyway, I'll have pictures uploaded tonight.

 

Not my picture, but it looks like this.

 

post-379279-0-93907500-1385700302.jpg

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Sounds like either bad jetting or gummed up carb. (probably both) Riding the bike hard with jetting like that will cause bad situations, lean 1 second, rich the other. This will cause heat to build, and well, you found out what happens then. 

 

The R9 or R8 won't make a huge difference, nor will the ES or EG - the EG is better at resisting fouling. Good jetting, and it won't matter the plug ever being fouled.

 

You're on the right track, start back with OEM jetting which to me was pretty good for sea level, consider 1 slightly leaner needle clip is where I ended up.

 

32:1 or 40:1 will be personal preference - remember, 32:1 has less fuel, and more oil, so this can have a slight effect on jetting..

 

Now that it's blown up, go through the entire motor again, I would check the run out on the crank/rod assembly, and plan on replacing them. 

 

Here's a few pics of a drilled wiseco:

 

http://s826.photobucket.com/user/rrrr1rob/media/CR%20500/2012-08-16034446.jpg.html

 

 

Yours will look more like this:

 

39_piston_drilled.jpg

 

The piston will come with directions on how to drill it.

 

Pic of why you drill the piston, it's to lubricate the small bridge seen here:

 

07_cylinder.jpg

 

For oil, stick with one of the higher ends, and be consistent. Fuel, you should be OK with an ethonal free premium fuel. Remember, you live near sea level, so you have a ton of oxygen there.

 

Let's talk about air filters - buy several of them. 3-4 is usually good. Before a day of riding, change the air filter for a clean and freshly oil filter. Remember, be consistent, how much oil you put on can change jetting. 

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Thanks a bunch for the picture. I'll double check tomorrow see if my current piston has those holes. It took me for ever to upload my pictures - living on the country side is a PITA.

 

I can definitely see (based on the picture of Socket), that my exhaust port\side took a hard shot.... There's missing chunk on my bridge... I hope to have enough time tomorrow to describe how the jetting were set, and where they are now.

 

Here's how my thing look like.

 

Edit: Looking at my pictures, seems like I did not have the mentioned holes drilled on this piston... I'll double check all around tomorrow.

Edited by Lemayilleur

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Not all pistons require drilling, but if i remember Wiseco does with a bridge. What kind of piston is currently in the bike?

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Thanks a bunch for the picture. I'll double check tomorrow see if my current piston has those holes. It took me for ever to upload my pictures - living on the country side is a PITA.

 

I can definitely see (based on the picture of Socket), that my exhaust port\side took a hard shot.... There's missing chunk on my bridge... I hope to have enough time tomorrow to describe how the jetting were set, and where they are now.

 

Here's how my thing look like.

 

Edit: Looking at my pictures, seems like I did not have the mentioned holes drilled on this piston... I'll double check all around tomorrow.

 

 

Only forged pistons require drilling.

 

That said, your piston and cylinder have suffered a catastrophic failure. That cylinder I think is too far gone for even welding - infact, when I look at it, it looks like you sucked dirt in the motor, and also ran it lean.

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As RBI said, stock jetting should look like this:

  • 2 turns for the Air Screw initial opening.
  • #40 for the Slow Jet
  • 3rd clip for the Jet Needle position
  • #420 for the Main Jet.

This is how it was set when we opened and cleaned the carb

  • 1.5 turns for the Air Screw initial opening.
  • #40 for the Slow Jet
  • 4th clip(one above 3rd) for the Jet Needle position
  • #410 for the Main Jet.

I'm no sure what this mean... Are those settings a big deal? Why are they all over the chart? Guess I'll never know lol.
 

Only forged pistons require drilling.
 
That said, your piston and cylinder have suffered a catastrophic failure. That cylinder I think is too far gone for even welding - infact, when I look at it, it looks like you sucked dirt in the motor, and also ran it lean.

 

What makes you think it sucked dirt (I assumed you mean sand, debris or what ever through the intake?)

 

running lean, I don't know - I guess the Jetting I've listed above will tell.
 
 

Not all pistons require drilling, but if i remember Wiseco does with a bridge. What kind of piston is currently in the bike?

 

I'm not sure, I didn't look for a tag. But it's irrelevant if I need a new one right?

 

 

Side note; in case it isn't clear in the pictures, the ring is stuck in the piston on the exhaust side. There's some scratch/scuff/rubbing on the exhaust side of the piston and cylinder. The worst seems to be the missing chunks around the exhaust bridge & port area.

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Well &%$#@! me, by looking at the pictures, looks like the piston that was put in isn't drilled.

 

So the bridge did not get lubricated and shit got hot / broke down. I'll inspect closely tonight, but based on Socket's explanation, those two little holes are right against the bridge... Exactly where everything rubbed, but I don't see the holes in my pictures.

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As RBI said, stock jetting should look like this:

  • 2 turns for the Air Screw initial opening.
  • #40 for the Slow Jet
  • 3rd clip for the Jet Needle position
  • #420 for the Main Jet.
This is how it was set when we opened and cleaned the carb
  • 1.5 turns for the Air Screw initial opening.
  • #40 for the Slow Jet
  • 4th clip(one above 3rd) for the Jet Needle position
  • #410 for the Main Jet.
I'm no sure what this mean... Are those settings a big deal? Why are they all over the chart? Guess I'll never know lol.

What makes you think it sucked dirt (I assumed you mean sand, debris or what ever through the intake?)

running lean, I don't know - I guess the Jetting I've listed above will tell.

I'm not sure, I didn't look for a tag. But it's irrelevant if I need a new one right?

Its relevant to try to find out why it blew up so it doesn't happen again. Figure out the pison tag or type( cast or forged). Then you can rule out the piston holes.

Jetting doesnt seem off by much, so unless the carb is gummed up, thats not the issue. Exhaust leak at the cylinder could make it extra lean also.

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Its relevant to try to find out why it blew up so it doesn't happen again. Figure out the pison tag or type( cast or forged). Then you can rule out the piston holes.

Jetting doesnt seem off by much, so unless the carb is gummed up, thats not the issue. Exhaust leak at the cylinder could make it extra lean also.

 

So one of the two piston doesn't require the holes? I'll inspect it tonight and find out. Edit: Just saw you already pointed this out, thanks!

 

Regarding the jettings, we're they pushing it on the leaner side as well?

 

I have now changed them back as close as OEM recommendation as possible:

 

  • 2 turns for the Air Screw initial opening.
  • #40 for the Slow Jet
  • 3rd clip for the Jet Needle position
  • #410 for the Main Jet.

 

I'm pretty sure I did have a leak on the exhaust port, the black oil that wasn't only running down the engine, it also looked like it sprayed a little bit on the sides of the bike when I drove it fast on my way home.

 

What do you guys recommend I do for the piston/cylinder? Not sure what my options are, but I'm always looking at reliability and durability when I fix things up.

Edited by Lemayilleur

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