1998 RM125 won't idle

I can't get this bike to idle so I'm giving up and going to the guru's.

info:

1) 1998 Suzuki RM125 with Keihin PWM36 carburetor

2) 0' above sea level, used for woods/backyard riding, it's currently ~30 degrees out

3) stock air box (new air filter 3 rides ago), stock carburetor, Eric Gorr 144 kit (relatively recent, probably ~40 hours? I have never disassembled the top end, bike feels about the same since I got it, and after the 40 hours of riding), and the reeds look intact (no chips)

4) currently has a 175 main jet and 48 pilot jet, needle 3rd position from top, air screw 1.5 turns out, gas/oil at 32:1, and float set to ~0.25". I have also tried different pilot jet sizes with no success (55, 50, 48, 40, down to a 35 to see if it needed to lean out, but I'm putting the 55 back in).

5) bike will not idle. The bike will start fairly easily (1-5 kicks), is responsive to an open throttle, and will run just fine when the throttle is opened, but when the throttle is closed, the bike stalls immediately

6) -the bike runs about the same when first started and when it warms up. -pulling the choke doesn't seem to help it start

-keeping the throttle open just enough so that it resembles an idle, and lifting the choke knob makes the bike bog and die

-twisting the throttle cable adjusters so that the slide is being raised slightly will make it idle, but the bike will take off under random conditions (namely when bars are turned to right, but not always).

-the bike's ability to idle is unchanged when the bike is warm

-turning the "idle adjust" screw opens the passageway and allows more air in; it has no affect on the bike's ability to idle when warm, or cold

-the bike starts to "ping" and will stay running by itself when the bike is almost out of gas

here the 55 pilot jet (I have new jets so I know they're clear):

IMG_4102.jpg

here is the cleared pilot jet passageway (the top branches out like a T, blew carburetor cleaner through it until it sprayed on the other side)

IMG_4107.jpg

here's the 170 main jet:

IMG_4101.jpg

here's the clear passageway on the main jet:

IMG_4104.jpg

and here's the float bowl (no sludge/gumming)

IMG_4105.jpg

that's all the information I could think of. If you need any further clarification, please don't hesitate to ask.

Thanks in advance.

update, I changed the pilot jet to a 62 to see if possibly the big bore kit needed a significantly higher amount of gas. It didn't help

So I changed all the settings back to 40 degrees, 0 degree elevation: 175 main jet, 58 pilot, needle clip 4th position from the top rode it around to make sure it was warm and parked it. As it sits, it still DOES NOT idle.

on the plus side, the bike does start first kick

have u adjusted your throttle cable up a little to take up slack your carb appears to be clean. so reinstall carb n try to take up the cable a lil bit all the jetting specs seem to be ok. take up cable on the top of carb cap not at the throttle .

just another thought also make sure where the idle adjust and choke knob are inside there needs to be clean i belive there is a air passage in that carb which allows the idle n choke to work propperly ck that as well hopefully u figure it out ik carbs can be a pain in the a**

have u adjusted your throttle cable up a little to take up slack your carb appears to be clean. so reinstall carb n try to take up the cable a lil bit all the jetting specs seem to be ok. take up cable on the top of carb cap not at the throttle .

thanks for the response

I've tried this before, but it lead to unpredictable and dangerous riding conditions (it just took off with my friend on it in 3rd gear around a turn and he crashed pretty bad). It doesn't always happen, but it will randomly take off if the throttle cable is adjusted to make the bike idle. The way the cable sits, it will always get a slight tug if the bars are turned, so taking out all the slack will change the throttle position when the bars are turned

Also, if you look at the microfiche, the throttle cable can't be adjusted at the carb, so I could only adjust it at the throttle.

SU0223_012.gif

1: CAP,CARBURETOR

just another thought also make sure where the idle adjust and choke knob are inside there needs to be clean i belive there is a air passage in that carb which allows the idle n choke to work propperly ck that as well hopefully u figure it out ik carbs can be a pain in the a**

Yes, that is correct. There is an air passageway that is used for both the idle and choke, and it is completely clear.

So I'm not really sure where to go from here...

Did you buy this bike new or used? Are you 100% sure the throttle cable thats in the bike is the stock/right throttle cable? I've had to mix and match cables in the field/ at track when that's all I had. Created some of the issues you're talking about. Maybe someone before you did this and didn't replace. In other words, the cable in the bike now is to short hence, the bike will idle if you adjust it but be unpredictable (to short).

Maybe a long shot however, it "seems" the problem is more in the "throttle slide" position than jetting at this time. Just a thought #@$%

I bought the bike used, but AFAIK, the throttle cable is stock (just based on the fact that it has a "bend" that matches the one in the fiche, and that it's routed in a way that goes through guides and openings that look stock).

Is there any other way to raise the throttle slide position without using the cable adjuster?

At the throttle, top pf the carb., or the idle screw only way I know.

....??..?.. The float needle/seat....... Did you change the float needle? I was talking to Honda last Friday and they were talking about bikes they had gotten in lately that had carb/idling issues. They said after they took the float needle and put it under a microscope they were able to find debris and cracks within the rubber part of the float needle and that this is what was creating their issues. I've never had this happen but, thought I would pass it on.... Also, these were four-stroke they were referring to, FYI

This is a long shot in the dark, however, here it is.

When I was a kid I changed out a set of handle bar on my bike and had similar issues when turning. I cut the bars down (making them narrower) and this fixed the problem. Hence, the bars I bought were to wide for the bike to begin with, regardless of if they were stock or after market bars.

The handle bars on the bike now, are they stock width? Are they wider that stock bars? If so, obviously this would create the turning issue we're been talking about.

Again, long shot but, you never know.

The same exact thing happen to me. Bike no longer would idle cause of an old stretched out cable. replace it, made it better but not yet fixed. Then adjusted the cable, wot when turning right because of oversized bars. Rerouted it so its on the right side of the steering column and has tons of slack, fixed.

Another idea, it seems that alot of peoples bikes all of a sudden have idle troubles, maybes is cause of all the crappy gas additives that they recently started putting in.

The same exact thing happen to me. Bike no longer would idle cause of an old stretched out cable. replace it, made it better but not yet fixed. Then adjusted the cable, wot when turning right because of oversized bars. Rerouted it so its on the right side of the steering column and has tons of slack, fixed.

Another idea, it seems that alot of peoples bikes all of a sudden have idle troubles, maybes is cause of all the crappy gas additives that they recently started putting in.

I think I'm just going to give the re-routing a shot...while I'm relatively sure the cable is stock, I'm not sure of whether the handlebars are, or not.

But even then, is that the proper way to get a bike to idle?

I feel like I'm ignoring the root cause here...

well the only things that effect the idle are valve height, valve cutaway, slow jet, mixture screw, don't quote me on this but maybe the needle diameter. only the valve height and mixture screw are subject to readjustment. If your bike suddenly stop idling that says one of those two things are out of position. If its not the mixture screw the your best bet is the valve height.

done...ordered a new throttle cable because the sheath on mine is starting to chip away. I'm going to re-route this new one on the right side of the bike to see if it'll help with the idle.

but if I take out all the slack to raise the slide, doesn't this break the cardinal rule of 3-8mm of throttle cable free-play?

well the only things that effect the idle are valve height, valve cutaway, slow jet, mixture screw, don't quote me on this but maybe the needle diameter. only the valve height and mixture screw are subject to readjustment. If your bike suddenly stop idling that says one of those two things are out of position. If its not the mixture screw the your best bet is the valve height.

hmm...maybe you're onto something here

the major key difference between the PWK36 and the PWM36 is in the idle circuit: on the PWK, the idle speed is controlled by a screw that raises or lowers the slide. On the PWM the idle speed is controlled by regulating the size of an opening on an accessory passageway.

Now, raising the slide (with the throttle cable) on my bike using the PWM will occasionally run the bike like it's idling. So if that's the case, maybe I need to swap out my PWM with a PWK because it allows me to control the slide height?

this assumes, of course, that there is still a root cause (possibly intake vacuum levels because of the big bore kit) that's keeping me from idling, but it can be circumnavigated by using a carb that allows me to alter slide height

another thing to add about the PWK, is that it is longer than the PWM and a has fins on the bottom of the intake; higher air velocity at low speeds. Check out my signiture.

I looked up your carb on the keihin website: instead of a mixture screw you have an air screw, does the same job but opposite. In place of an idle speed screw you have cable adjusters on the top of the carb.

to make things more confusing, the PWM that came on the 1998 RM125 is different from the PWM that you'll find on the Keihin website: the RM version is a PWM36mm, doesn't have the option of alternative slides, and does not have a cable adjustments on the cap. The Keihin website has a PWM38mm which does have aforementioned options. If you look at the fiche on the first page, you'll see that

so yeah...the RM PWM36 has been a little aggravating...

either way, the throttle cable came in, so I'll try re-routing it and taking out the slack

I also bought a used non-AirStriker PWK36 on ebay, so either way, I'll have the option of adjusting idle by raising the slide internally

but thanks for the offer on the PWK38

Please get back with us and let us know how this turns out. This is a interesting thread for me.

The PWM and PWK use the same jets, i don't know about needles though. So if you get the carb and the jetting is totally off swap you jets and possible the needle.

Please get back with us and let us know how this turns out. This is a interesting thread for me.

absolutely :thumbsup:

and sorry about not responding to your earlier comments, but to follow up, I never did change the float needle, and while it's possible that it his minute holes, I think it's unlikely

with the bars, it is possible that they're aftermarket, so I'm going to try re-routing the new cable I picked up to fix the slack issue

and lastly, you mentioned idle screw earlier, which I'm going to try with the PWK carb, since it has a regular idle screw

The PWM and PWK use the same jets, i don't know about needles though. So if you get the carb and the jetting is totally off swap you jets and possible the needle.

definitely a plus! I currently have a dozen brand new pilot jets! this bike will always have perfect jetting so long as I own it...

Well did you swap out the carb?

ha, ha! I see you have responded to me before I responded to you!

unfortunately it's not here yet...I won the carb on fleabay 3 days ago, and the seller sent it parcel post, so it probably won't make it here until Monday (which is coincidentally the day I'm having the suspension worked over by the shop...so I can't put the carb on until I get the bike back, on Friday).

but if it works, then it would fit my theory: the carb is perfectly clean, and the reeds are fine; instead the bike won't idle because boring it out change the intake vacuum levels. So to compensate for it, the way to "force" the bike to idle, is to raise the crap out of the slide (which you can control with a PWK, but you can't with a PWM).

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