So I need help with an 2004 RM 125

msp138
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msp138
Edited Date/Time 5/22/2017 3:57pm
Well I thought it'd be fun to buy a 125 like I used to race when I was younger. Kind of get away from the 450 for a couple practices. I bought the bike with riding it with a "jetting" issue. The problem is the bike runs great on the stand. Revs flawless and starts right up first or second kick. Once I put it in gear and run it all hell breaks. As soon as the power should kick in it loads up or runs like it's not warmed up. So bottom of the gear great, top is horrible. I will now list the shit I already checked on it because I feel like I've tried everything.
I have:
Checked reeds
Cleaned powervalves and reinstalled them correctly
Rebuilt carburetor and put back to recommended jetting specs
replaced stator and magneto
Repacked silencer and checked if pipe was clogged
I've tried to advance or retard timing to no luck
I've also ohm checked the ignition coil

My next steps are replacing reeds (just in case)
Buying the really expensive spark plug that Suzuki recommends
Buying a new CDI box

Any other advice would be appreciated. I'm just at a loss. Thanks

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Paw Paw 271
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Paw Paw 271 4/29/2017 7:25pm
4/29/2017 7:25pm
Have you done a compression test? If so, what was the reading?
Have you done a leak test? If so, how log did it hold 6psi of pressure.
Have you done a vacuum test? How log did it hold?
How are your power valves adjusted?
Have you set the float height?
Have you checked the kill switch?
The parts you replaced...Are they OEM or aftermarket?

Paw Paw
bronwynrayne
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bronwynrayne 4/29/2017 7:58pm
4/29/2017 7:58pm
Paw Paw 271 wrote:
Have you done a compression test? If so, what was the reading? Have you done a leak test? If so, how log did it hold 6psi...
Have you done a compression test? If so, what was the reading?
Have you done a leak test? If so, how log did it hold 6psi of pressure.
Have you done a vacuum test? How log did it hold?
How are your power valves adjusted?
Have you set the float height?
Have you checked the kill switch?
The parts you replaced...Are they OEM or aftermarket?

Paw Paw
Did you ever get a t-shirt for your help on here or do I need to get on the horn with Guyb again?
msp138
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msp138 4/30/2017 4:30am
4/30/2017 4:30am
Paw Paw 271 wrote:
Have you done a compression test? If so, what was the reading? Have you done a leak test? If so, how log did it hold 6psi...
Have you done a compression test? If so, what was the reading?
Have you done a leak test? If so, how log did it hold 6psi of pressure.
Have you done a vacuum test? How log did it hold?
How are your power valves adjusted?
Have you set the float height?
Have you checked the kill switch?
The parts you replaced...Are they OEM or aftermarket?

Paw Paw
No compression test but replaced the piston thinking the previous person might have installed something wrong.
I don't know what a leak test or a vacuum test is (sorry For the ignorance)
Going to check the float height but won't that effect the bike revving up on the stand?
Do you just un hook the kill switch? To test it?
I replaced most oem parts but they are eBay finds
The reeds are v force.
Thanks for the help. I'm interested about the kill switch as to why that would effect the top end at load.
Paw Paw 271
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Paw Paw 271 4/30/2017 6:16am
4/30/2017 6:16am Edited Date/Time 4/30/2017 6:16am
Leak and vacuum test are the way to test crank seals and other gaskets to be sure nothing is leaking either under pressure or in the transfer of fuel and air.
Yes the kill switch can vibrate and cause it to kill the spark when it is vibrating. Disconnect it.
The float level is very important as the engine rpms come up under long load times the fuel can be used up in the float bowl and create fuel starvation and or flooding is set too low or too high that you can't duplicate while the bike is on the stand as the rev time is much shorter.
If the stator is not OEM, then that could be your issue cause. I have seen too many after market or rewound units do some weird things.
The basic starting point of trouble shooting is to know the basic's of your engine status, like the compression, leak testing and vacuum testing. With out these basics you are just shooting in the dark.
Assume nothing!

Paw Paw

and no to the T-shirt question.

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msp138
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msp138 4/30/2017 4:29pm
4/30/2017 4:29pm
Paw Paw 271 wrote:
Leak and vacuum test are the way to test crank seals and other gaskets to be sure nothing is leaking either under pressure or in the...
Leak and vacuum test are the way to test crank seals and other gaskets to be sure nothing is leaking either under pressure or in the transfer of fuel and air.
Yes the kill switch can vibrate and cause it to kill the spark when it is vibrating. Disconnect it.
The float level is very important as the engine rpms come up under long load times the fuel can be used up in the float bowl and create fuel starvation and or flooding is set too low or too high that you can't duplicate while the bike is on the stand as the rev time is much shorter.
If the stator is not OEM, then that could be your issue cause. I have seen too many after market or rewound units do some weird things.
The basic starting point of trouble shooting is to know the basic's of your engine status, like the compression, leak testing and vacuum testing. With out these basics you are just shooting in the dark.
Assume nothing!

Paw Paw

and no to the T-shirt question.
So I don't have access to a vacuum or leak tester. I did get frustrated after the float height was good. I used an oem stator other than the original. My dad came over for dinner and I picked his brain ( he's a machinist and the one who built and worked on all my bikes growing up). He convinced me it was the power valves. I decided to check it once more. I pulled the cylinder and he said that the exhaust valve isn't flush with the cylinder when open. There is a sleeve and it looks like valve only goes to where the sleeve starts. My dad said he can't remember but that doesn't look right. The cylinder I found out needed two gaskets or the piston will hit the head. You think I'm screwed and need a new cylinder? That's gotta be the reason why it is just bogging on the top end. I took a picture it show what it looks like.

Dtat720
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Dtat720 4/30/2017 5:08pm
4/30/2017 5:08pm
Is it smoking when loading up? Sounds more like a crank seal leak
xnationalwrench 4/30/2017 7:47pm
4/30/2017 7:47pm
You said you installed the power valve correctly but have you checked to see if they open and close while the engine is running?
Paw Paw 271
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Paw Paw 271 5/1/2017 4:31am
5/1/2017 4:31am Edited Date/Time 5/1/2017 4:32am
What does the underside of the piston look like?
I see a lot of wear in the cylinder.
Paw Paw
msp138
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msp138 5/1/2017 8:42am
5/1/2017 8:42am
Paw Paw 271 wrote:
What does the underside of the piston look like?
I see a lot of wear in the cylinder.
Paw Paw
I'll take a picture of it when I get home but it doesn't have even an hour on the piston since I replaced it. I'm confused as to if the exhaust valve should be flush with the inside of the cylinder when fully opened which mine is not.
ehr400
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ehr400 5/1/2017 8:57am
5/1/2017 8:57am
it should be closed or closer to the cylinder when idling and upper RPM's valve should open. Have you cleaned or serviced them recently?

One thing I read concerned me, you said you had to double stack the base gasket so the piston doesnt hit the head, you sure you have the right piston in it? Also has the head been shaved at all?

I ran the wrong plug in my YZ250 one time and it would miss on the top end as well. Also went thru a kill switch issue with mine recently.

msp138
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msp138 5/1/2017 9:31am
5/1/2017 9:31am
ehr400 wrote:
it should be closed or closer to the cylinder when idling and upper RPM's valve should open. Have you cleaned or serviced them recently? One thing...
it should be closed or closer to the cylinder when idling and upper RPM's valve should open. Have you cleaned or serviced them recently?

One thing I read concerned me, you said you had to double stack the base gasket so the piston doesnt hit the head, you sure you have the right piston in it? Also has the head been shaved at all?

I ran the wrong plug in my YZ250 one time and it would miss on the top end as well. Also went thru a kill switch issue with mine recently.

Well I didn't trust the guy before me so I decided to re do the top end and clean out the powervalves. I noticed after I took it apart again that it was hitting the head so I looked at the old gasket it had on it and it was doubled up. I didn't notice at first bc of all the yamabond that was on it. I think they shaved the cylinder down.
Bruneval
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Bruneval 5/1/2017 1:07pm
5/1/2017 1:07pm
Are you using the flat top piston? In 2004 the RM125 cylinder changed to use the long rod motor and the crank, cylinder and head is a different configuration. If you have a 2003 or older cylinder it will be shorter in length and might be why you have an interference issue with the piston contact. Your cylinder should look like this.







msp138
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msp138 5/1/2017 1:17pm
5/1/2017 1:17pm
Bruneval wrote:
Are you using the flat top piston? In 2004 the RM125 cylinder changed to use the long rod motor and the crank, cylinder and head is...
Are you using the flat top piston? In 2004 the RM125 cylinder changed to use the long rod motor and the crank, cylinder and head is a different configuration. If you have a 2003 or older cylinder it will be shorter in length and might be why you have an interference issue with the piston contact. Your cylinder should look like this.







That's what my cylinder looks like. I am using a stock piston. I looked everywhere and I haven't found any part for a flat top piston or flat top head. I've hear this but I haven't found any info on it.
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Bruneval 5/1/2017 1:33pm
5/1/2017 1:33pm
If it's the stock piston, it should be flat across the top to be correct for your cylinder. The pre-2004 pistons had a raised dome in them, so check you've got the right one just to be safe.

Have you checked your squish clearance? In simple terms, it's the measurement between the piston and the cylinder head. Should be about 1mm (I forget the exact figure), but if you've never done it before it's a pretty simple job using a piece of solder - lots of how to videos on YouTube for this. It's a crucial measurement and if you're having to double-up on base gaskets, your cylinder and head may have been decked so the additional base gaskets are a way of increasing the gap to achieve the correct squish measurement.
Paw Paw 271
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Paw Paw 271 5/1/2017 3:53pm
5/1/2017 3:53pm Edited Date/Time 5/1/2017 3:55pm
Too bad you did not mention the double base gasket thing to start off with.
The flat top vs domed piston is a real issue as the pistons will fit, but the squish will be way off.
Also, the cylinder shows a lot of wear.
The underside of the piston photo?

Paw Paw
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Falcon 5/1/2017 5:08pm
5/1/2017 5:08pm
The electronic parts catalog for 2004 does not indicate a dual base gasket.
msp138
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msp138 5/2/2017 4:19am
5/2/2017 4:19am
Paw Paw 271 wrote:
Too bad you did not mention the double base gasket thing to start off with. The flat top vs domed piston is a real issue as...
Too bad you did not mention the double base gasket thing to start off with.
The flat top vs domed piston is a real issue as the pistons will fit, but the squish will be way off.
Also, the cylinder shows a lot of wear.
The underside of the piston photo?

Paw Paw
Yeah I didn't check the old gasket until my dad mentioned to check it. It had so much yamabond on it I didn't see it doubled up. I realized this bike was made a race bike then sold to a weekend guy that just didn't know how to fix a bike. I have a new cylinder ordered and I'm going to start from scratch with stock everything. Weird thing though I have no idea why someone decided to shave down the powervalves. I'm guessing it was a big bore at one time and they needed the clearance. I'll post a picture. Thanks for your time paw paw. The more I dig into this bike the more I realized it's not normal principles of fixing a bike bc it has been clustered together just to run then sold to me.

Paw Paw 271
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Paw Paw 271 5/2/2017 4:36am
5/2/2017 4:36am
The biggest problems will be obtaining replacement valves. They will be hard to find and cost to get them.

Paw Paw

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ehr400
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ehr400 5/2/2017 5:12am
5/2/2017 5:12am
Paw Paw 271 wrote:
Too bad you did not mention the double base gasket thing to start off with. The flat top vs domed piston is a real issue as...
Too bad you did not mention the double base gasket thing to start off with.
The flat top vs domed piston is a real issue as the pistons will fit, but the squish will be way off.
Also, the cylinder shows a lot of wear.
The underside of the piston photo?

Paw Paw
msp138 wrote:
Yeah I didn't check the old gasket until my dad mentioned to check it. It had so much yamabond on it I didn't see it doubled...
Yeah I didn't check the old gasket until my dad mentioned to check it. It had so much yamabond on it I didn't see it doubled up. I realized this bike was made a race bike then sold to a weekend guy that just didn't know how to fix a bike. I have a new cylinder ordered and I'm going to start from scratch with stock everything. Weird thing though I have no idea why someone decided to shave down the powervalves. I'm guessing it was a big bore at one time and they needed the clearance. I'll post a picture. Thanks for your time paw paw. The more I dig into this bike the more I realized it's not normal principles of fixing a bike bc it has been clustered together just to run then sold to me.

If the motor was ported or BB'd like you said there would be PV mods. I have a feeling there is something simple that the PO mixed and matched on the motor.

My buddy has a 2004 RM125, I should have looked closer at his when we did his top end so I could give a better reference.

I was going to say come down to Coops some time and ride that 125 in the sand. Lol Maybe I will run into you sometime and check it out in person.
msp138
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msp138 5/2/2017 6:31am
5/2/2017 6:31am
ehr400 wrote:
If the motor was ported or BB'd like you said there would be PV mods. I have a feeling there is something simple that the PO...
If the motor was ported or BB'd like you said there would be PV mods. I have a feeling there is something simple that the PO mixed and matched on the motor.

My buddy has a 2004 RM125, I should have looked closer at his when we did his top end so I could give a better reference.

I was going to say come down to Coops some time and ride that 125 in the sand. Lol Maybe I will run into you sometime and check it out in person.
I go to supercoops a bit. I usually tend toward Baja or twisted. Yeah if you see me at the track come say hi. I'm hopefully going to get my cylinder and Motorsport has the power valve in the OEM section so I'll get it all together once I find the correct head.
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ehr400 5/2/2017 7:46am
5/2/2017 7:46am
Cool man, I live about 10 minutes from there. Kinda wrote off Twisted as much as I want to have 2 tracks there. Well you see a YZ250 with blue rims and #797 come and say hi.

I am interested to see what differences you have on the new cylinder.
msp138
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msp138 5/2/2017 8:09am
5/2/2017 8:09am
ehr400 wrote:
Cool man, I live about 10 minutes from there. Kinda wrote off Twisted as much as I want to have 2 tracks there. Well you see...
Cool man, I live about 10 minutes from there. Kinda wrote off Twisted as much as I want to have 2 tracks there. Well you see a YZ250 with blue rims and #797 come and say hi.

I am interested to see what differences you have on the new cylinder.
I gotta ask why did you write off twisted? I have nothing vested in the track but when I go there is seems just fine. If you don't want to go into details I get it but I am just curious.
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ehr400 5/2/2017 8:56am
5/2/2017 8:56am
Well, honestly when they took over for the prior owners I was pumped, my buddy did the orginal dozing on the track and design. It had alot of promise and seemed like going in right direction. Now it seems like the track isnt really prepped, the track layout is not working, and different operators running dozer which has alot of differences it seems like. Also been going to Coops since 2006-07 and there is some behind the scenes things that happened that I think was uncalled for.

msp138
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msp138 5/3/2017 5:06am
5/3/2017 5:06am
ehr400 wrote:
Well, honestly when they took over for the prior owners I was pumped, my buddy did the orginal dozing on the track and design. It had...
Well, honestly when they took over for the prior owners I was pumped, my buddy did the orginal dozing on the track and design. It had alot of promise and seemed like going in right direction. Now it seems like the track isnt really prepped, the track layout is not working, and different operators running dozer which has alot of differences it seems like. Also been going to Coops since 2006-07 and there is some behind the scenes things that happened that I think was uncalled for.

Ah gotcha. Yeah I don't go there enough to see the difference. Baja is my go to track.
msp138
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msp138 5/9/2017 6:15pm
5/9/2017 6:15pm


So since I was ignorant of the flat top piston head and how it is radically different I took a side by side photo of the difference. Just an update I have a new cylinder just waiting on the powervalves in the mail to put it all back together. I hope this will help out someone else that may be confused. Buying a used bike is the definition of gambling. I'll keep posting the progression. Thanks guys
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FGR01 5/9/2017 7:29pm
5/9/2017 7:29pm
Yeah, if I had to guess, some previous owner ran that as a BB and that is why the PV was cut back. Then they blew it up and re-sleeved it back to stock bore size but left the cut PV in it.

Also, a buddy has an RM125 about same year as this. Stock jetting was horribly rich, like a 470 main or so? He ended up having to lean that way out to get it to run clean. It was a very low hour, tight bike, no other probs.
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Bruneval 5/9/2017 7:40pm
5/9/2017 7:40pm Edited Date/Time 5/9/2017 7:43pm
FGR is right. That's definitely a big bore cylinder head on the right. Here's mine from my RM144.

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chump6784 5/9/2017 9:32pm
5/9/2017 9:32pm
FGR01 wrote:
Yeah, if I had to guess, some previous owner ran that as a BB and that is why the PV was cut back. Then they blew...
Yeah, if I had to guess, some previous owner ran that as a BB and that is why the PV was cut back. Then they blew it up and re-sleeved it back to stock bore size but left the cut PV in it.

Also, a buddy has an RM125 about same year as this. Stock jetting was horribly rich, like a 470 main or so? He ended up having to lean that way out to get it to run clean. It was a very low hour, tight bike, no other probs.
My wife had an 04 RM125, when we got it the main jet was a 440, ended up going to a 360 I think to get the thing right. Also had to lean the pilot right out too.
msp138
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msp138 5/19/2017 5:13pm
5/19/2017 5:13pm


So I finally got my stock cylinder, stock head and stock main powervalve. I put it all together and the thing rips. The amount of relief I felt when the bike ran thought the gears flawlessly was something else. No I can finally spend money to make it look good. With the amount of money I put into the engine it might be naked this year lol
msp138
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msp138 5/22/2017 9:53am
5/22/2017 9:53am
So...... I took my bike to the track again with fresh stock cylinderOEM,piston and ring, stock head OEM, and new powervalve OEM installed. The bike ran great for half of a lap then started running funny. I went back and noticed my spark plug backed out. Oh great I thought I didn't tighten it down enough. I tighten it back up and went for a spin again. Same thing happened. Changed my spark plug to another one and it did it again. i heard this could be caused by detonation. I am using a BR8EG plug instead of the really expensive recommended stock plug R6918B-8. Has anyone had that problem? I'm baffled as to why the plug backed out multiple times with all stock OEM components.

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