rm 125 cuts out

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rmrider45

Member
Sep 8, 2008
171
0
i have a 2003 rm 125 and on the weekends like to go out with my son and climb coal hills .i dunno where to start on the problem with this bike.top end has 20 hours on it, reeds are good no cracking and seal good.i mix 93 pump gas with klotz
40:1. bike just seems when your wide open on a big coal hill it seems to be like cutting out or blocked. i am not sure of the number of the main jet .is this issue i am having in the jetting.on trails the bike runs great. but when you have it wide open it seems to like sputter on hills.dunno if i should put in a bigger jet or a smaller main jet.

wait let me refrase this 1/4 throttle its fine wide open it seems like its blocked:(
 
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sharky243

Member
Dec 14, 2008
246
0
First off, I'v'e had bad luck with klotz. Their oil seems like it's really "concentraited", there for it seems to make a rich mixture. I would first try a different oil like Belray or Amsoil. Next, if you are still having the issue, have a look at the burn on the plug. If it looks like a black, oily, sooty mess, then the main jet is too large. It also wouldn't hurt to throw a new plug in it. Be sure to gap it properly !!!. It could also be a high speed ignition miss. This would meen some serious testing time on a rainy day with a multimeter. Try the simple things first, and give it a hard hot run to clean it out.
 
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Chili

Lifetime Sponsor - Photog Moderator
Apr 9, 2002
8,062
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Time to take the carb apart and start with a good cleaning making sure there is no blockages in any of the jets. Once you know you are starting with a spotless carb make a note of the jet sizes and work from there.

Depending on the jetting we also had a bit of a detonation problem with our 03 and had to up the octane to cure it.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
An 03 running 40:1, thats not in the book? Why so much fuel and no oil? Most riders, 32:1 is not enough oil. What plug are you running? The motor needs, the ignition and the top end checked, or just way too much gas is making it cut out. 125's and smaller, try 25:1. The bike will last longer and make a lot better power. Learn to jet it properly. Running an engine with what, a seven hour or so mark on the rings/piston, you need a lot of oil, not gas. Vintage Bob
 
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rmrider45

Member
Sep 8, 2008
171
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25:1 wouldnt that make it smoke real bad and foul plugs?
i am running a br8es plug in the bike
or maybe thats the problem i am trying to run it leaner when it needs to be running richer

but a week prior to this i tried some yamalube and mixted it more richer like 30:1 and it fouled the plug and this bike never fouled a plug ever
 
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Chili

Lifetime Sponsor - Photog Moderator
Apr 9, 2002
8,062
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Pick a ratio and an oil and then stick to it, we ran 32:1 Yamalube 2R in our 03. I'd also suggest once you get the bike sorted to start using the stock plug or you could be in for a world of hurt when the groundstrap on that BR8 let's go on you.

Our final jetting for the 03 for general summer riding was 460 Main, 35 Pilot, up one on the clip and I can't recall the air screw setting. My kid was pretty quick and we were having some detonation issues or I likely would have leaned the main another step.
 
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rmrider45

Member
Sep 8, 2008
171
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460 Main, 35 Pilot are these the stock jets ?
also i will put a br9es in today which is the correct plug?
 
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Chili

Lifetime Sponsor - Photog Moderator
Apr 9, 2002
8,062
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460 Main was the stock main for a USA spec'd bike ours in Canada came with a 560 and the bike would barely run. 35 Pilot is two sizes down as stock was a 40. The stock plug is an NGK R6918B-8 and before you come back and reply, yes I know it's expensive ;) I would stick with the BR8's until you get the jetting sorted out and then switch to the stock plug.
 
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brentn

Member
Aug 7, 2009
42
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Is that ratio what your manual calls for? you are technically enriching the mixture by running more gas than oil. Most manuals call for 32:1 for specific reasons, one of them is that the jets are designed for this mixture.

If that doesn't help, take the carb off and pull out the main and pilot and use a bottle of carb cleaner and clean out all the passages well.
 
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sharky243

Member
Dec 14, 2008
246
0

Actualy by running more gas then oil you are thining the mix out. 32:1 is the average recomended mix.
example: <.....16:1(rich)...............50:1(lean)......>
32:1 = 32 parts fuel : 1 part oil
 
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brentn

Member
Aug 7, 2009
42
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Yea lean oil mixture, I'm just talking about gas.


More parts gas means a richer fuel mixture and a leaner oil mixture.

At least this is how it was explained to me in another thread I was reading..
 
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rmrider45

Member
Sep 8, 2008
171
0
i think i found the problem. when i was going to take the carb off and clean itand i looked and the air/fuel mixture screw was gone.i had an extra carb lying around and put the spare screw in the carb .cleaned everything good and put a new plug in it and it fired up one kick.didnt have time to ride it yet tho.btw the main jet is a 460. i think this could explain the cutting out.it didnt know when it was rich or lean.or it being out it was running lean the whole time :ride: :ride: :ride:
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
I sure hope your carb did not ingest too much foreign material. Make sure you have all the parts, and none is left deep inside the carb. Vintage Bob
 
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