97 RM125 running issue

Skizza · Jun 16, 2015

Hi,
I have just finished putting a new top and bottom end in my 97 RM125, my issue is when I give it the message it breaks down, I found that it doesn't do it in the higher gears. It goes like a rocket in 4th and up but 1st, 2nd and sometimes 3rd it breaks down in the higher revs. When it first did it it would foul up the plug and die after about 2 mins, I have moved the needle to its leanest setting and put a BR8ES plug in it. The plug doesn't look fouled after a 5 minute ride and it runs better, but still breaks down in the lower gears.
I should mention I bought the bike in pieces with a blowen up motor so I have no idea how it ran previously. Iv'e cleaned out the carb so it is spotless, Main jet is 168 (don't think this is stock) pilot is 50. The bike also seemed to run better with the muffler off, I checked it for blockage but it isn't blocked, may just be coincidence as i was playing with the needle position when I rode with no muffler for about 100m.
I'm new to 2 strokes so this is all learning for me, I don't know if im running rich or lean to cause the break down. Any help or advice what to check and how to check it would be awesome, I really want to get out for some good fun on this bike.

2strokesteve89 · Jun 16, 2015

Skizza:
Hi,
I have just finished putting a new top and bottom end in my 97 RM125, my issue is when I give it the message it breaks down, I found that it doesn't do it in the higher gears. It goes like a rocket in 4th and up but 1st, 2nd and sometimes 3rd it breaks down in the higher revs. When it first did it it would foul up the plug and die after about 2 mins, I have moved the needle to its leanest setting and put a BR8ES plug in it. The plug doesn't look fouled after a 5 minute ride and it runs better, but still breaks down in the lower gears.
I should mention I bought the bike in pieces with a blowen up motor so I have no idea how it ran previously. Iv'e cleaned out the carb so it is spotless, Main jet is 168 (don't think this is stock) pilot is 50. The bike also seemed to run better with the muffler off, I checked it for blockage but it isn't blocked, may just be coincidence as i was playing with the needle position when I rode with no
muffler for about 100m.
I'm new to 2 strokes so this is all learning for me, I don't know if im running rich or lean to cause the break down. Any help or advice what to check and how to check it would be awesome, I really want to get out for some good fun on this bike.

You said the plug doesn't look fouled, what does it look like (tan light brown dark tan, black etc...) you may have the carb jetted right but is the float set properly, what is your pre mix ratio? Also you may have the carb set up ok and have a spark problem maybe check the coil, plug wire, do you have a manual? It may have some of the tests for these components in the manual.

Skizza · Jun 16, 2015

Plug looks a dark tan colour, I set the float to 16mm it doesn't overflow sitting straight but if I lean the bike a little it will overflow, I may be wrong but I believe that is correct? Premix ratio is 32:1. I don't have a manual but I plan to get one. I was thinking of putting a timing light on it and making it fail, then if it's a spark issue the timing light will tell me that, not sure if it's a solid way to tell though.

2strokesteve89 · Jun 16, 2015

Skizza:
Plug looks a dark tan colour, I set the float to 16mm it doesn't overflow sitting straight but if I lean the bike a little it will overflow, I may be wrong but I believe that is correct? Premix ratio is 32:1. I don't have a manual but I plan to get one. I was thinking of putting a timing light on it and making it fail, then if it's a spark issue the timing light will tell me that, not sure if it's a solid way to tell though.

Sounds like you may have the carb set correctly, unless you missed somthing, but the plug color seems to indicate you didn't. I was thinking you may want to recheck the reeds for chipping or cracking, but my bet is your looking at a spark issue.

Skizza · Jun 16, 2015

The thing that confuses me is it doesn't do it in the higher gears, it goes real good and fast. I'm not too sure about having the needle on the leanest setting (top clip) could this cause damage by being too lean? I guess I'll try the timing light trick and see if that tells me anything. I will check the reeds out later too.

ossagp · Jun 16, 2015

if the float is indeed set to shutoff at 16mm and is still overflowing when leaned, then you need some parts. you can check to see if the float needle is indeed capable of shutting off the fuel flow buy holding the float at 16mm and blowing like you are exhaling through the fuel line. easier to do if you use a longer piece of hose so you can hold the carburetor body up at eye level. open and close the float valve and see what kinds of leaks you may be getting. keihins as they age will get leaks around the brass sleeve that the needle rides in as well as leaking at the needle. the over rich mixture will show up at the higher rpms and higher vibration levels encountered in the lower gears more.

i run oil mixes from 20 to 1 down to 16 to one, and that has nothing to do with missing but will change a plug color. you learn to know what that looks like after awhile.

Skizza · Jun 17, 2015

Checked the reeds, they algood. Double checked float height (16mm) and checked float needle for correct operation. So I took it for another test, it broke down in first when I took off but after that went fine, through all gears I rode up and down for about 10 minutes with no issues at all.. I did take off when the bike was cold, do 2 strokes have issues before they warm up? (I've never owned a 2 stroke before so I don't know the ins and outs). The bike was in pieces for about 2-3 years before I got it, maybe it's a case of needing a good run to clear out? I dunno I'll keep riding to see if it plays up anymore... I have the needle on the top clip, will this be too lean or cause any issues? Thanks for the help.

ossagp · Jun 18, 2015

So did you get it to quit dribbling fuel when leaned over?

Skizza · Jun 18, 2015

Yeah it doesn't spill fuel out on a lean anymore.. Going to give it A good ride on the weekend. Not sure what Iv'e done but it ran good last night when I rode it.

jackson409 · Jun 18, 2015

Warm up your bike good before going out on a ride. Fastest way to seize one is to ride it while it's still cold.

ossagp · Jun 18, 2015

Skizza:
Yeah it doesn't spill fuel out on a lean anymore.. Going to give it A good ride on the weekend. Not sure what Iv'e done but it ran good last night when I rode it.

Good idea. Now that you have the basics covered (like gas where it is supposed to be) you can get to know it a little before chasing the smaller stuff. It isn't uncommon for a new rider, or someone new to a different type of bike to feel like his jetting is over rich to begin with. A few hours into ringing one out, the rider finds it suits his needs or is lots closer to it than he thought.

Skizza · Jun 18, 2015

Okay cool thanks guys will post up how it goes after my ride tomorrow.

Skizza · Jun 24, 2015

So took a mate out for a ride, he rode the RM and I rode my KTM.. The RM went perfect for about 30-45 mins, we where playing in some soft sand (i'm not too sure what my mate was doing as I was on my bike) but to cut to the chase it blew the big end bearing and partially seized, got the motor turning over again so wasn't, fully seized. I'm not sure what caused this to happen, I think it would have got too hot though as it was being revved in soft sand not really moving.. It sucks because i have just rebuilt this motor and now have to do it all again. I'm going to buy a manual and set the bike back to complete stock when I rebuild it again. Anyone have any better ideas why it would have done this? or ways to help prevent it next time. I had a 32:1 oil/fuel mix.

2strokesteve89 · Jun 24, 2015

Skizza:
So took a mate out for a ride, he rode the RM and I rode my KTM.. The RM went perfect for about 30-45 mins, we where playing in some soft sand (i'm not too sure what my mate was doing as I was on my bike) but to cut to the chase it blew the big end bearing and partially seized, got the motor turning over again so wasn't, fully seized. I'm not sure what caused this to happen, I think it would have got too hot though as it was being revved in soft sand not really moving.. It sucks because i have just rebuilt this motor and now have to do it all again. I'm going to buy a manual and set the bike back to complete stock when I rebuild it again. Anyone have any better ideas why it would have done this? or ways to help prevent it next time. I had a 32:1 oil/fuel mix.

Possibly an air leak from either the left side crank seal or from the intake boot at the Reed cage, this could lean out the fuel mixture enough to seize it. What was the temperature if it was much colder than what it's jetted for this could cause problems also. you'll know more when you take it apart, if you got blue discoloration on the bearings then they were overheated most likely from lack of lubrication.....let us know what you find with some pics of the failed parts.

ossagp · Jun 24, 2015

Old engine run a little too hard can do it. A new top end putting out good power again will sure show the next weakest component. Needle bearings run hotter as they loosen up than they do with zero lash.