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02 RM 125 Carb Problems

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Hi All, 

 

BACKGROUND:

I've read and re-read all of the rich Jetting articles supplemented here for this bike. This coupled with studying the service manual, and random articles and still can't figure out my bikes issue. When I acquired it recently it hadn't been started in 7 years. I removed the carb and cleaned the heck out of it. I used a moose racing carburetor kit to replace all jets/needle/gaskets with new. Needle clip set at 2nd position. I've checked the float height and it is within spec. Air screw is turned out 1.5. This bike is like brand new now, so periphery items shouldn't be affecting it. Reed valves look good, but haven't completely removed because I don't want to wait for a new gasket before an upcoming dunes trip. 

 

THE ISSUE: Starts fine, first kick, runs fine for a while. I notice the issue is namely with the main jet as when I open up the throttle the issue starts at 3/4 range. It revs fluidly until it hits 3/4 and then it makes a sound like a governor makes when revved to it's limit. Also, I was doing a coolant flush the other day and noticed while trying to run it for an extended period it randomly climbed in throttle without touching it. From idle it starts to climb by itself until it gets to maximum throttle and I have to shut it off with the kill switch. Removing the plug, it has a little bit of black to it, not much. 

 

CONSIDERATIONS: Bike is equipped with an FMF fatty pipe and consulting FMF's jetting guides I am far from the what they prescribe. My moose kit came with (assumed) stock jets. Main is 460, pilot is 40, etc. FMF shows that an 02 should run a 430 Main and a 27.5 Pilot with stock needle position. Will this simply solve my issue?

Also, if an 01/02 suzuki share the same carb, why would FMF show that the main jets are different. For the 01 it is 450 for main instead of 430. Is this more related to their stock numbers and design of pipes or the carbs themselves? I ask because My '02 carb had a stripped pilot insert and so I used an 01  had laying around which was fine and looked identical with the same part numbers. 

 

CONCLUSIONS: Because I ride in the dunes, is it wise to buy a jet kit? Or just a few anticipated jets from the dealer? Am I totally ignorant, but with how pertinent jetting is to the proper function of this bike, wouldn't it have been prudent to provide owners with a contained of "all jets which may be necessary"? Or maybe they did?

 

Thanks for your opinions and advice... 

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to me, it started out just sounding like a main jet issue until you brought up " From idle it starts to climb by itself until it gets to maximum throttle and I have to shut it off with the kill switch. "  To me, that last sentence makes it sound like some type of air leak.  A leak down test can eliminate/confirm an air leak.

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Thank you for the insight. I noticed that the fuel vent was clogged with grease, would that be associated? I replaced all of the jets and it runs better now, but still has periodic mid-throttle weird response. so I'm not sure what else to do with that darn needle, lol. 

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Very small air leak.  Buy or make a leakdown tester.

Make sure you jet a bit richer for the dunes, the additional load and sustained WFO riding can be devastating when it runs a bit lean.

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Very small air leak.  Buy or make a leakdown tester.

Make sure you jet a bit richer for the dunes, the additional load and sustained WFO riding can be devastating when it runs a bit lean.

 

Hi Matt, 

Man, I wish I would have read this two days ago :(. I went to the dunes and it ran poorly. Again, mid-throttle. If I held it in the mid it just kinda acts like it doesnt know it wants to go faster or die all together. Kind of a sputterin I guess, but never stopped running. In fact at one point ran better. Ultimately, I got annoyed after playing with the carb so much and am thinking you're precisely right about an air leak. I think messing with jetting is nonsensical at this point after how much time I've spent on that. Do you have any recommendations for a diy leak down tester? Or where to buy one? I'm going to do that next. Wouldn't that affect the bike in all throttle ranges though? Why is it still only happening at mid. 

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All the parts from Lowe's; I built mine out of all pvc, with a gauge located in the gas aisle.  I used an expanding rubber freeze plug for the exhaust, shoved a bolt into the power valve vent line, and some Teflon tape over the pvc that fit into the reed manifold to make for a tighter fit.  Total cost was about $20.  I did find that over tightening the reed manifold to pvc pipe only caused it to leak, making readings impossible.  Backed off the clamp and it was great.

 

http://www.allthingsmoto.com/forums/f-14/17-leak-tester-2-stroke-13912/

http://martysgarage.info/2012/12/cheap-diy-two-stroke-leakdown-tester/

 

Really small air leaks can be almost intermittent in nature, affected by temp, vibration, humidity, etc.  It's easier to deal with a big air leak than a tiny one; they're easier to find.

 

While you have the pipe off the bike, look up the exhaust port at the piston for blowby.  If you were running it at the dunes with an air leak, it's likely the piston needs to be replaced.

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MattFisher, 

 

Thanks so much for the info and links! I'm going to get to this asap. I hope I didn't mess up my piston. Compression reads 180, but it was emitting a small amount of blue smoke when revved at the dunes, so I hope I didn't damage it, is it possible to just replace rings to remedy or do you think a top end will be necessary. I feel irresponsible for taking it out there without it functioning right. I was convinced it was running rich, lol. That's why I took it out. It always seemed to run better the further the air screw was turned out. Usually the best at 1.5-1.75 turns out. So I dunno. I'll start with air, sucks to have to do mechanical work towards the end of nice weather when you should be riding. 

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Run the leakdown test first to figure out where the leak is coming from.  A bit of blue smoke is normal on a 2 stroke, btw.

 

If the piston looks great from the exhaust port (and intake port) then you could certainly gamble on fixing the air leak and running it.  If it doesn't look great, pull the cylinder, and look at the underside of the piston (along with the rest of it.).  There's loads of images and info on what a piston should look like, 5 minutes online and you should have a pretty good idea.  If it's been run lean, there should be a spot of carbon on the underside of the piston caused by the crown getting so hot it burns the oil on the underside of the crown in addition to what's happening in the combustion chamber.  This can also be assisted by not having an oil that matches your riding such as having an oil with a low flash point but you run the piss out of the bike (can you say- dunes).

 

As for just replacing the rings, that depends on the condition of your piston and taking measurements of it would behoove you too.  Once they wear, it's time to replace.  When my son was on the 85, I put a new ring in every 5 hours and a fresh piston every 10.  Kept it fresh, strong and reliable.  My 250 motors could go for 10 times longer, but I don't ride anywhere nearly as hard as he does, bigger motors last longer, and I don't need every little bit of power possible.  180 psi on a 125 is fine, though that alone is not an indicator of the condition of the piston, just what kind of ring seal you have.

 

An hour meter is a really nice and cheap insurance policy, btw.

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Run the leakdown test first to figure out where the leak is coming from.  A bit of blue smoke is normal on a 2 stroke, btw.

 

If the piston looks great from the exhaust port (and intake port) then you could certainly gamble on fixing the air leak and running it.  If it doesn't look great, pull the cylinder, and look at the underside of the piston (along with the rest of it.).  There's loads of images and info on what a piston should look like, 5 minutes online and you should have a pretty good idea.  If it's been run lean, there should be a spot of carbon on the underside of the piston caused by the crown getting so hot it burns the oil on the underside of the crown in addition to what's happening in the combustion chamber.  This can also be assisted by not having an oil that matches your riding such as having an oil with a low flash point but you run the piss out of the bike (can you say- dunes).

 

As for just replacing the rings, that depends on the condition of your piston and taking measurements of it would behoove you too.  Once they wear, it's time to replace.  When my son was on the 85, I put a new ring in every 5 hours and a fresh piston every 10.  Kept it fresh, strong and reliable.  My 250 motors could go for 10 times longer, but I don't ride anywhere nearly as hard as he does, bigger motors last longer, and I don't need every little bit of power possible.  180 psi on a 125 is fine, though that alone is not an indicator of the condition of the piston, just what kind of ring seal you have.

 

An hour meter is a really nice and cheap insurance policy, btw.

 

I've ordered the hour meter. I pulled the spark plug recently to do another compression test and look at what I found. Doesn't this plug suggest it's actually been running rich as opposed to lean? I've also noticed billowing white smoke out of the exhaust now, but my coolant is full so maybe it's the dreaded crank case seal everyone complains about.   :(

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The condition of the plug, combined with the billowing white smoke suggests you're drowning the plug in transmission fluid.  The good news is that you don't need to split the cases to change crank seals (except on some Kawi's).

 

How does the piston look when viewing it through the exhaust port and intake port?

 

You might as well pick up crank seals and plan on replacing them.

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I live in mass and my 02 ran crisp and perfect at fmf jetting specs. I had an fmf sst and a shorty. I had a problem with me reed bolts backing out on mine and letting air in

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2002 Rm125 carb, the problem is the carb slide.  You need to have it cut 1mm or buy a replacement slide that is 1mm leaner.  the 02 was very rich from idle to 1/4 throttle.  You can not adjust the pilot jet or air screw to fix this hiccup.  You can patch it with a leaner slide needle, but the best fix is the 1mm leaner slide.  Replace the slide and you will notice a huge improvement from idle to 1/2 throttle.  It will pep up the bike all the way to full throttle and then you will be able to jet to your riding conditions or mods.  

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Padgett gave me some pretty good advice when I refurbishing my 02 rm125 in december 2012.   

 

I have had such good results with RB Designs and their carb mod/head squish mod on my gasgas ec300 that I am considering sending my rm125 cylinder and carb this winter. 

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The condition of the plug, combined with the billowing white smoke suggests you're drowning the plug in transmission fluid.  The good news is that you don't need to split the cases to change crank seals (except on some Kawi's).

 

How does the piston look when viewing it through the exhaust port and intake port?

 

You might as well pick up crank seals and plan on replacing them.

Matt, 

 

Thank you, sorry for my delay in reading this. I heard that was  a common problem on these. I guess i got myself into a bit more than I thought in this bike. WIsh I didn't spend so much time on jetting since that wasn't even the primary source of my issues. I'm going to look at the piston tomorrow. I'll take a pic. 

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2002 Rm125 carb, the problem is the carb slide.  You need to have it cut 1mm or buy a replacement slide that is 1mm leaner.  the 02 was very rich from idle to 1/4 throttle.  You can not adjust the pilot jet or air screw to fix this hiccup.  You can patch it with a leaner slide needle, but the best fix is the 1mm leaner slide.  Replace the slide and you will notice a huge improvement from idle to 1/2 throttle.  It will pep up the bike all the way to full throttle and then you will be able to jet to your riding conditions or mods.  

Thank you padgett, 

 

I think my problem is sources elsewhere. After I eliminate that, if it still isn't jetting correctly, it's good to know I can replace the slide. I have two of them currently. One is stamped 5.0 and the other 5.75. I think the other is from the 01 Suzuki. 

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