125cc 2 stroke starts

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9/6/2017 12:39 AM

Found a mint 04 rm 125. Still had original tires on it. When I bought it, clutch was slipping. installed a new clutch plate kit.rebuilt the top end and cleaned the carb. Now I have been riding it for fun. I been thinking about racing it. Went to practice a couple starts and it will not start In 2nd gear... I've never had a bike that did not like starting in 2nd gear. I believe the front sprocket is a 13 tooth and 50 tooth rear. Anyone else had this problem? I feel like a complete goon coming here to ask lol but the bike runs good. It's pretty slow, it's a stock 125 so II ride it pretty hard but bogs off a 2nd gear start. Thanks in advance for any responses and this is the BEST mx forum

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9/6/2017 2:16 AM

Jetting might be off or youre not high enough in the rpms.

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

9/6/2017 5:16 AM

mississippihippie wrote:

Found a mint 04 rm 125. Still had original tires on it. When I bought it, clutch was slipping. installed a new clutch plate kit.rebuilt the top end and cleaned the carb. Now I have been riding it for fun. I been thinking about racing it. Went to practice a couple starts and it will not start In 2nd gear... I've never had a bike that did not like starting in 2nd gear. I believe the front sprocket is a 13 tooth and 50 tooth rear. Anyone else had this problem? I feel like a complete goon coming here to ask lol but the bike runs good. It's pretty slow, it's a stock 125 so II ride it pretty hard but bogs off a 2nd gear start. Thanks in advance for any responses and this is the BEST mx forum

2nd Gear starts are a tall ask for a 125, how much do you weigh? Most guys I know start in 1st gear.

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9/6/2017 5:21 AM

You have to feather the clutch out with the throttle pinned if you plan on starting in second gear.

Paw Paw

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9/6/2017 5:34 AM

1st gear left foot up shift when you get over the gate

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9/6/2017 2:30 PM

Around 145lbs with gear. I have tried in really high RPMs. Guess it's normal.

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9/6/2017 8:25 PM

If your bike is jetted correct you should be able to start in 2nd gear at high RPMs.

Maybe look into some other jetting options?

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9/6/2017 8:43 PM

CarlinoJoeVideo wrote:

If your bike is jetted correct you should be able to start in 2nd gear at high RPMs.

Maybe look into some other jetting options?

45 year old vet here from nz
vet race bike 17 crf450 , yz125 for fun in 2nd class.

After a long time from racing a two stroke , and that was yz250s I have found it a little tricky to get it
right. I have been trying second but on sand only for now and that makes it easier to bog.
high rpm and feather that clutch all the way out the gate . I have got better but you have to be so precise.
The 125 is such a hoot to ride. first gear would be easier but you will need to shift asap off the gate, drop the revs a little and you still may bog if not perfect. my bike is jetted perfect! v voce 4, and full fmf system . gearing will play o large role in this to , what is on your rear wheel ? I run a 50 tooth.

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9/6/2017 8:56 PM

My son always started in 2nd gear no problem with his ktm 125, no bog or hesitation and he held her wide and dumped the clutch. He weighed about 130 at the time

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9/6/2017 9:21 PM

All of my two strokes would start in 2nd no problem. Then the fourstroke came and never thought back. Now I'm back on a 2 stroke. I'll loOk into the jetting. Even tho I hate jetting. Might as well get some reeds and a pipe while I'm there

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9/6/2017 9:30 PM

Maybe u could have the head milled also, check the squish and see if there is any room to mill it. It definitely sounds underpowered or something. You could also match the cases, a friend that I was training and did the motor work on had an 04 rm 125 also and it scooted out of the gate in 2nd no problem. Hopefully u get it figured out

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9/6/2017 10:38 PM

There was another thread not too long ago where we discussed RM125 jetting. The stock jetting in these bikes was horribly rich. They had to be leaned way out. And even when jetted properly they are not the most powerful bike around.

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Powerband in every gear !

9/7/2017 12:37 AM

Think I should try a carb rebuild kit first? The bike is pretty old and sat most its life. Best part is that I bought the bike from a girl . Right now I'm starting to miss fuel injection

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9/7/2017 3:21 AM

My wife had an 04 RM125, it came with jetting that fmf recommended, something like a 440 main. I ended up going with pro circuit jetting which was around a 360 main and leaner pilot too. It went much better.

As for starts, I'm 187lbs without gear. Raced my wife's yz125 the other week cos i bent my front disk in a crash. 2nd gear, wide open and let the clutch go aggressively, maybe a couple flicks if the dirt was really tacky but just gotta hold it wide

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9/7/2017 7:06 AM

mississippihippie wrote:

Think I should try a carb rebuild kit first? The bike is pretty old and sat most its life. Best part is that I bought the bike from a girl . Right now I'm starting to miss fuel injection

I may be wrong, but I do believe the rm had stock a 12 tooth front sprocket, and not a 13 which may be your problem. A 125 should do a start in second (feathering clutch). Look up to see what oem gearing was for that year, I got a feeling that maybe your issue if the front is a 13 like you said.

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9/7/2017 11:03 AM

mississippihippie wrote:

Think I should try a carb rebuild kit first? The bike is pretty old and sat most its life. Best part is that I bought the bike from a girl . Right now I'm starting to miss fuel injection

mxracer10 wrote:

I may be wrong, but I do believe the rm had stock a 12 tooth front sprocket, and not a 13 which may be your problem. A 125 should do a start in second (feathering clutch). Look up to see what oem gearing was for that year, I got a feeling that maybe your issue if the front is a 13 like you said.

Yup I think your right, the front is a 12 stock, I'm pretty sure

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9/7/2017 2:25 PM

I will double check when I get off. Will a 13 tooth front sprocket make that big of difference.

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9/7/2017 2:32 PM

mississippihippie wrote:

I will double check when I get off. Will a 13 tooth front sprocket make that big of difference.

Yes.

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9/17/2017 10:23 PM

Well I ended up finally getting on a gate at a local Alabama race and it started just fine in 2nd gear...

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9/18/2017 2:23 PM

I used to holeshot 125 races all the time by starting in 2nd.

This method works for concrete:
Clean the gate really well;
Do a short burnout to lay down some rubber on the pad;
Hold it at about 3/4 throttle while slipping the clutch out in 2nd. It should be trying to creep a little. Hold your bike back with both legs down in front of the footpegs. Your body should be centered but leaning forward slightly;
When the gate drops, wick the throttle to WFO while lifting your toes off the ground. Let the clutch feed out for the first 15-20 feet out of the gate. Don't let it all the way out until you are rolling pretty fast.

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Braaapin' aint easy.

9/18/2017 2:37 PM

I always started in 1st on my 125's. Always has great starts.

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Tomac and/or Anderson for 2020.....

9/18/2017 3:14 PM

Paw Paw wrote:

You have to feather the clutch out with the throttle pinned if you plan on starting in second gear.

Paw Paw

Agreed, I used to start in 2nd racing 125s and you want to be very high RPM and slow on the clutch release. A hair too fast and you will bog quickly.

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9/18/2017 4:24 PM

hassbeen wrote:

2nd Gear starts are a tall ask for a 125, how much do you weigh? Most guys I know start in 1st gear.

What?? 1st gear is just stupid on any bike. Gotta feather the clutch, and listen to the bike.

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9/22/2017 6:02 PM

I use to pull 3rd gear starts on my 125's, but I didn't weigh but 115lbs too....

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9/23/2017 1:34 AM

Put on the stock tires again and you will be abloe to start in 4th gear lol

Nah but like mentioned before, you will need to work the clutch a bit.

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KX125