RM 125 jetting issue

2strokes4life · Mar 20, 2010

Alright guys I know what you're thinking. Oh great can't he read the jetting link. This problem is driving me nuts. Here is what happens. I have a 2002 RM 125. I bought it with a messed up top end. It has a new cylinder, wiseco piston kit, new fatty pipe, and new FMF silencer. The bike idles like a champ. When you put it in gear and take off, it bogs big time off idle. If you grab a handful of throttle off idle, it will bog so bad that if you keep it wide open it will die. If you ease past this point, it does hesitate a little before the powerband but then responds pretty well in the zone. I tried buying the JD jet kit and this didn't solve the problem. I called them and they sent me a larger pilot jet. I've tried different main jets, needles and needle positions. It acts like crud in the carb. I've had the carb off and blew carb cleaner through it, but have never soaked it. I'm always a little leary of the soaking chemical. I'm not sure what to remove when soaking one. I have been troubleshooting this since the fall. I gave up over the winter and tried again today with the larger pilot from JD. No luck! I'm ready to turn this over to a mechanic unless you guys have any last ditch ideas. Thanks in advance for any ideas.

robwbright · Mar 20, 2010

Did you remove the jets and blow compressed air thru them? If you didn't, then you didn't really clean the carb.

Are the reeds in good shape?

dmaegan · Mar 20, 2010

hmmm

start at the beginning

1-fuel filter
2- fuel petcock( including the petcock filter inside the tank)
3-fuel hose swelling or partially swelled shut
4-carb float height
5-blow out pilot circuit with compressed air
6-check for air leaks at the reed cage and boot assebly
7-if all these are fine try running with the chocke on to see how that does if it runs better try lowering the clip on the needle jet
8-how many turns is your air screw out.

2strokes4life · Mar 20, 2010

1. There is no fuel filter other than the one in the tank on the petcock. It was taken out and cleaned.
2. New fuel line from the tank to the carb.
3. carb cleaner was sprayed in carb while apart. All jets were taken out and blown through with high pressure from air compressor with a blowgun nozzle.
4. I have tried various needle and jet combinations.
5. Reeds are new carbon fiber and sitting flat.
6. The cylinder is new and had all new gaskets. I didn't leak test after installation, but I think if there were an air leak I would see it in RPM's. I've done a lot of topends and never had an air leak.
7. Float height is spot on.
8. Airscrew is 1.5 and idles perfect.

I will try running it with the choke on tomorrow and see what happens. I don't think it is going to work though. When I start it with the choke it runs at a higher rpm until I drop the choke. Starts on the first or second kick. I usually give one full compression stroke then push it just until it has resistance then kick it over. I only start it this way when cold.

dmaegan · Mar 20, 2010

hmm what about the reed cage gaskets?

they are a very easy place to leak and cause a lean mixture and just for gp reasons to clear up and make sure it is not starving for air although what you describe is to much air warm it up and run it just briefly with the air filter off.

does it if you quickly crack the throttle when it comes back to idle rev high and then drop slowly?

and can you slowly give it throttle up until 1/4 throttle and if so does it surge when holding it at 1/4 throttle?

dmaegan · Mar 20, 2010

oh you said you blew through the jets but have actually blown out the pilot circuit of the carb itself?

2strokes4life · Mar 21, 2010

It does not stutter very badly if you slowly turn the throttle. Once in a while it will briefly hesitate before the powerband. I'll do some testing today with the choke open. I blew out every hole I could find in the carb, jet holes, nozzle, vent holes, and etc. Originally I blew out all of the jets, but now every jet is new from JD. Thanks for the help all. I guess it's ready for the pros to work on. This shade tree mechanic is at the end of his rope with this project bike. By the way I live in Ohio. We are around 1000 ft and it is about 60-70F right now. I have carbon fiber reeds, fatty pipe, FMF shorty silencer, and a uni air filter. These are all new. Just out of curiosity what jetting is anyone with similar conditions running? As always thanks.

2strokes4life · Mar 21, 2010

Alright here's the update. I warmed it up and turned the choke on. It ran a ton better almost no hesitation. It still wasn't crisp and snappy off idle, but I know that can be cured with the airscrew once I get the correct jetting. Here's the problem though. I don't know if I have an air leak or not. I am not getting any eratic idle or unusually high rpm's. The problem is, this jetting is way off of JD's recommended settings. Does this mean I have an air leak leaning it out or could that be normal for this bike? I started wondering about the fit between the reed cage and the intake boot. There is no gasket there. I didn't remember replacing it during the top end rebuild. I pulled up the parts pics and there is not a gasket listed. Should I use RTV or leave it alone? I'm not sure if there is a leak there or not.

dmaegan · Mar 21, 2010

has the air cleaner lid been modified?
or could there be a leak on the snorkle going from the back of the carb to the air cleaner box.

but if it ran better with the choke on then it is deffinately lean what ever size jet you have in the pilot right now after checking for leaks if there are none go 1 size larger pilot jet then you have now.

that should solve the issue and every bike is independent of it selve jetting guidelines are exactly that a guideline the exact same bikes could use different jetting.

your 1.5 with the air screw now you would have to screw it in to richen it up at this pooint leave it 1.5 out and go 1 up on the pilot jet.

dmaegan · Mar 21, 2010

there should be a gasket there check a parts cliche to be certain but I would think there should be a gasket between the reed cage and the cylinder that might be the air leak. warm it up and while running spray some starting fluid around the reed cage boot to see if the idle rises.not to much starting fluid though small burst with nozzle about 1 foot from the cage.go all around the cage like that

2strokes4life · Mar 22, 2010

I checked for air leaks tonight with starting fluid. No air leaks. I sprayed around the reed cage, both intake boots, the cylinder head, and the cylinder. One more thing off of the list.

2strokes4life · Mar 23, 2010

I have a question for you all. One of the posts asked me if the airbox lid has been modified. The airbox was one of the items that needed parts when I bought the bike. There was no airfilter and the bolt and a few other airbox parts were missing. It doesn't have a lid on it right now. Only the seat and the rest of the airbox is covering the filter. Would it be running too lean because of a UNI filter and no airbox lid? If yes, then maybe the problem is solved.

dmaegan · Mar 23, 2010

yes that is exactly why it is running lean when you remove the air filter lid it will let 5 times the amount of required air in even if the filter is on the bike you will not notice it as much at higher gearing ranges as you will the bottme end.

replace the air cleaner parts then rejet back to what it needs to be go back down on the jets.be careful to get it right lean conditions will severely damage a engine.especially a faster higher reving 2-stroke

_JOE_ · Mar 23, 2010

I may be wrong but I don't think an RM125 has an air box lid. I wouldn't think the filter would cause it to go lean, unless you had rejetted it with a dirty filter before.

How far from stock are you on the pilot? What fuel are you running?

Chili · Mar 23, 2010

That bike does indeed have an air box lid stock, the first thing we did was remove the lid. I likely have one laying around from and 03 or an 05 if you want one. I seriously doubt it is the cause of your issue as it's not a sealed unit that you have to cut off, just a slip on lid that covers 2/3 of the air box to keep water from directly dripping on the filter.

dmaegan · Mar 23, 2010

you beat me 2 it chilli I just checked cliche.I am not sure how much extra air it would allow in if it is not a sealed unit though.But if he is as high as he is on the pilot and all air leaks were ruled out and he is still lean It might be possible.He said when he ran it with the choke on it went from bog to hesitate so with the choke on it appears to be slightly rich so even leaving the lid off he would still have to go up 1 on the pilot probably. but I also believe since the pilot is only responsible up to slightly over 1/8 throttle even his needle seems a bit lean he might want to get the cover just to rule it out

2strokes4life · Mar 23, 2010

I currently have a 40 pilot (original is a 35), JD's needle (blue on 3rd slot), and a 420 main jet. It kind of makes sense. If this machine were bone stock, I'm sure the 35 would be ok. But with the lid gone, a twin air filter, and FMF exhaust system you would expect more air flow. That's why we buy these mods isn't it? I am kind of wondering if the lid will solve or not. I hate to buy the lid and it not work. My only doubt is because the seat is covering it now. Like was said also, it isn't a sealed system. I will try it. It's worth a shot. If anyone has a lid they would lone for the test I will definitely send it back and buy my own. If the lid helps I will probably keep it. I am surprised that the JD kit wasn't just a drop in. It was for my Honda CR 250, but it's all stock. I never did get any answers about jetting settings for any 2002ish RM 125's running similar mods. I know all bikes are different, but I just wondered if anyone is as far off stock as I am. I've always thought that 1 jet size off of stock was usually enough.

dmaegan · Mar 23, 2010

its like this the seat covers it yes but does not sit tight to it

what can you suck more air through a straw or a garden hose and why

the hose the hole is bigger that did not sound right but only analagy I could think of

now to test it just get your self a piece of carboard and just cut it half the size of the air box and duct tape it around tight so only half the air box is open then start it up I bet it smokes alot more and hesitates or sounds like a weird diesel. then do it again and this time cover 3/4 of the air box it will even be worse

that will tell you but you could just get 1 or 2 size larger on the pilot unitl the bottom is jetted right but you will probabaly then find out the your needle is needing to be richened as well as your main jet.as you get your jets right it will point out problems in the rest of them until they are all right.

my kdx was so rich by stock standards I removed the air box lid completely and raised the clip 1 slot to lean the needle and dropped the pilot 3 sizes and I have fmf rev pipe fmf turbine core muffler boyessen power reeds and a oversized bore so I can not speak for the rm125 of yours but my kawi was so rich you could have put 50000 miles on it without any fear of motor lockup but it ran like crap in the process

_JOE_ · Mar 24, 2010

Why put the lid back on? Just keep jetting until you get it right. What led you to set the air screw at 1.5 turns? Have you gone further? The air screw and pilot jet work as a team. If the pilot is too small it will run better and better as you turn the air screw in.

whenfoxforks-ruled · Mar 24, 2010

Not 1 indication of a lean condition, yet still chasing it? When started cold, does it run better with the choke on? When its warmed up, and bogging, does putting the choke on make it run better? When you replaced the cylinder, was it modded? Is the head modded? When the cylinder was replaced, how was the condition of the bottom end? Is the exhaust valve working correctly? Screwy jetting issue, there is a mechanical issue somewhere. Vintage Bob

helio lucas · Mar 24, 2010

whenfoxforks-ruled said:
Is the exhaust valve working correctly?

:nod:

Chili · Mar 24, 2010

I must admit I haven't given this thread much time as I'm on vacation with limited PC access but we have never owned an RM125 (had 4 of them) that we had to go richer on the pilot, almost without question I've ended up 2 or 3 pilot jets smaller than stock. And before you point to your "mods" we run every bike without the lid, twin air filter and a Pipe either FMF or PC on our RM125's a few of them also had the cylinder and porting modified.

I think you may be going the wrong way with the jetting. For reference one of the members here who I trust for advice was running his 02 RM125 on a 25 pilot and even tried leaner, most of the pipe makers spec'd a 27.5 or 30 pilot for the 02.

dmaegan · Mar 24, 2010

2strokes4life
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Join Date: Apr 2009
Posts: 39

Alright here's the update. I warmed it up and turned the choke on. It ran a ton better almost no hesitation. It still wasn't crisp and snappy off idle,

correct me if I am wrong that indicates lean and the opening post said it was bogging badly

whenfoxforks-ruled · Mar 24, 2010

Yes, seemingly lean? Not on the pilot though, idle is perfect and the air is 1 1/2 out. Cylinder bore out of round, power valve malfunction, bad bottom end? Was the head modded? Or just a bent/worn needle, clip way off, wrong needle, tps solenoid, wrong/worn slide? Warm it up, get it to bog, kill it and see if the plug is wet or dry? Vintage Bob

2strokes4life · Mar 24, 2010

Here are some clarifying points. I haven't had a chance to test the bike. My wife has been in the hospital the last 2 days. She's 40 and they think she had a stroke. Tell me that doesn't suck. They ran through all of these tests and couldn't find anything wrong. And to think I am only having easy jetting issues. Good thing I'm not a doctor (mechanic either). Well here we go. I appreciate all of the support on this.

Idles perfect. Changing the airscrew position doesn't seem to have an effect on the idle speed. I know the AS doesn't affect the idle speed, but when jetting it shoud increase in rpm's to the highest point and then back off a little for course adjustment. It is at 1.5 turns. The entire top end is factory new with no mods. When the bike is cold the bog doesn't seem to be as bad. When I get it warm the bog off idle is so bad that if you hold the throttle open once it starts to bog it will die. I ran it with the choke open warm and it helped immensely. I bought the bike used. I don't know what all was done to it before. Bottom end seems rock solid. Shifts smooth and crank appeared fine. Little side to side, no up/down. I was having trouble with this bogging after the rebuild. When I bought the bike there wasn't even a piston in the cylinder. I new it was bad. The cylinder had a huge long gouge. I wonder if the top end went from being lean. I am really paranoid about running lean (even a little). I bought the JD jettting kit to take the easy route out. They are the ones that said it needed to go a little richer. They sent me the 40 pilot. That is the biggest they had is what I was told. I'm sorry for all the hassle guys. I'm going to try this airbox lid fix and if that doesn't work unless someone has a another idea it's going to Suzuki. I already called and they said it shouldn't cost me much and that it's probably just a simple issue. I HATE to GIVE UP, but I am just a shadetree mechanic. I would really rather ride than wrench on it any longer. Time to start putting that $500 plus parts to use.
Vintage Bob - I will bog it and pull the plug. Great idea and
I should have already done that. I apologize!

RM 125 jetting issue

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RM 125 jetting issue

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