Jump to content

Jetting Mystery 1996 RM125


Recommended Posts

I recently purchased a 1996 RM 125. Before I purchased I did a compression test on the cylinder and it registered 120psi. A new top end was in my near future. The bike didn't idle which I attributed it to the low compression.

I decided to dive in and inspect the top end, upon taking the exhaust off, about 1/4 cup of black ooze came out of the main pipe. The silencer was clear, but the packing as completely oil soaked. Spark plug black also, but not fouled. All indications were that the bike was running rich. Cylinder was smooth, piston looked to be in good shape. no carbon build up on the head, or exhaust. Power valve operates smoothly.

Part of the rebuild, I inspected the carb(PWK 36) and cleaned all the jets. Reeds looked good, there are the Carbon Fiber type. Airfilter, dirty, but not clogged.

Here is the mystery. The manual I have states the stock jetting is #170 for the main and #50 for the slow jet. Upon inspecting the jetting of the carb, it had a #150 for the main jet and a #45 for the slow jet. That seems really far from the standard jetting, and toward lean.

I am thinking of going back to the stock jetting after the rebuild. Was wondering if anybody has any ideas of why the jetting may be moved towards lean, but still running rich? I noticed most of the jetting kits don't go back to 1996 Suzuki's, can someone recommend a jetting kit for this carberator(PWK36). Also, I know the reeds are not stock, could that be a reason for the jetting change?

Link to comment
Share on other sites

If you dont feel you have any mechanical issues or air leaks, then your next step would be to properly jet the bike on a long straight path, mark the throttle, and hold at throttle setting coinciding with jetting circuit. You didnt mention where the pilot air screw was set. Remember that when anything goes up( temp, humidity, or elevation) then your jetting will be richer. Use a certain premix and stay with it. 32to1 is a good baseline, and use premium fuel as the oil will reduce your octane rating. ProCastor 927 is a good premix. I wouldnt worry about what jets are in the bike until proper jetting methods tell you different.

Link to comment
Share on other sites

The airscrew has no effect. The idle screw is all the way in, max speed, no idle. Cleaned the jets no effect. I am concerned about running with the #150 jet if if the previous owner was compensating for something and end up running to lean on a new top end. I am using Yamalube 2S at 32:1.

Link to comment
Share on other sites

No it is all stock i think, could not find any identifying markings, except the warning that it does not meet federal noise guidelines. The silencer is definitely stock.

I did notice a big dent where the waterpump runs close to the pipe. This does not look stock. From what I understand this can detune the whole system, am I correct?

Link to comment
Share on other sites

  • 3 weeks later...

Here is an update. I did the ATF fluid in the trans to see if the crank seal was bad. It smoked like mad, with the tell tale white smoke. The previous ownder must have mistaken burning trans fluid for it running rich.

I will be replacing both the Flywheel side and the clutch side seals.

I performed the bearing test on the flywheel side and it is still tight(in and out, up and down), but on the clutch side, there is very slight motion. Can't see it, can only feel it. I would like to hold off the repair until this winter. Does anyone have any experience with this. I know I am on borrowed time, but since the season is almost over, I would just like to ride the rest of the season and then replace I am guessing less than 10-15 hours total. I do not race, mostly trail ride.

Link to comment
Share on other sites

  • 4 weeks later...
  • 7 months later...

I think I am finally getting somewhere with regards to this mystery. It seem to boil down to a mid throttle problem. I have tried the largest needle diameter R1471 and the bike runs much better, but I still foul plugs. I ride some light MX and some trials, so throttle is tyically half or less.

This is what I'm thinking. The PWK carb that comes with the bike does not have a replaceable needle jet and it is most likely worn oval, since the bike is 15 years old with a unknown history. Even with the larger diameter needle jet, the off idle response is still rich. I am thinking of modifying the slide, or replacing it with a #6 or #7 from JD jetting($50:banghead:) to compensate. The stock slide is #5. I have read quite a few threads and this seems to be the magic knob I haven't been able to turn.

Anyone have any experience modifying a slide (in a garage, not a machine shop)? Or point me in a direction to where I could send the slide in. I figured if I screw it up, I'm no worse off. I found a thread somewhere on the web, and now I can't find it again:banghead:

Link to comment
Share on other sites

what is ATF test, how do you chek if the seal is bad?,

I have read putting Automatic Trans Fluid(ATF) in the gearcase make the bike smoke like mad if the crank seal is bad because it is thinner than 30W oil. I guess it is a substitute for a leakdown test. Hope this helps. I replaced both my crank seals.

Link to comment
Share on other sites

  • 3 months later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

×
×
  • Create New...