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St. Paul-ish, MN
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So I'm working on my co-workers 2002 RM125 that he picked up last summer for $500 - down the molehill we go.
He asked me to fix it up on his dime, so I did all the normal stuff to the chassis, new tubes, replaced some spokes, new cables, repacked the silencer...blah blah etc.
Now the problem - The engine has a mean stutter when riding it when it tries to come on the powerband - wont clean out and almost sounds like a misfire. Will clean out an run well when warm on the stand.
Here's what I've done and checked: Nothing has worked. (FSM = factory service manual)
-Head re-cut back to stock specs by Williams Moto Werx
-New piston ring
-Piston has 2~hrs on it
-Cylinder measured in spec (End of spec it has a steel sleeve) on a CMM
-Cleaned PV
-New Boyesen Reeds
-Cleaned carb
-Jetted per FMF spec
-Reset float height per FSM
-New Plug
-Verified PV is functioning
-Re-set PV spring tension per FSM
-New Airfilter
-Brand new FMF Factory Fatty
-Verified Electrical components (Coil, stator, kill switch) with multimeter and FSM
I'm leaning towards a bad CDI box, or maybe slight chance of left side crank seal leak (All thats left to check lol).
Anyone have any insights, sanity check, or a 2001-2007 RM125 CDI box laying around I can borrow to check bikes performance? Or that they want to sell?
He asked me to fix it up on his dime, so I did all the normal stuff to the chassis, new tubes, replaced some spokes, new cables, repacked the silencer...blah blah etc.
Now the problem - The engine has a mean stutter when riding it when it tries to come on the powerband - wont clean out and almost sounds like a misfire. Will clean out an run well when warm on the stand.
Here's what I've done and checked: Nothing has worked. (FSM = factory service manual)
-Head re-cut back to stock specs by Williams Moto Werx
-New piston ring
-Piston has 2~hrs on it
-Cylinder measured in spec (End of spec it has a steel sleeve) on a CMM
-Cleaned PV
-New Boyesen Reeds
-Cleaned carb
-Jetted per FMF spec
-Reset float height per FSM
-New Plug
-Verified PV is functioning
-Re-set PV spring tension per FSM
-New Airfilter
-Brand new FMF Factory Fatty
-Verified Electrical components (Coil, stator, kill switch) with multimeter and FSM
I'm leaning towards a bad CDI box, or maybe slight chance of left side crank seal leak (All thats left to check lol).
Anyone have any insights, sanity check, or a 2001-2007 RM125 CDI box laying around I can borrow to check bikes performance? Or that they want to sell?
If you need a CDI, I have a spare one from a 2005 (I fitted a factory ignition). Will need to work out getting it over to the States as it's back in the UK, so will take a few weeks.
Bob - my only experience with a bad right side crank seal was that it would smoke a ton all the time on my old YZ250. It does smoke when it tries to come on the pipe, I have one more leaner main jet coming, if that doesnt work I will have to figure out a leak down test.
The Shop
Except 1st/2nd it runs great. 3rd-6th on the road it runs perfect. Came home, gapped a new plug, same thing. The kicker is the electronics on this bike are dumb enough it doesn't know what gear its in...
I'm going to replace crank seals on a whim and see if that does anything, otherwise I'm stumped.
The other issue you may run into is with the TMX carb. There's a tiny gasket (about 3/8" square) that goes between the carb body and where the slide bottoms out. There are two screws under the float that allow you to remove the piece; I think it's called the needle jet holder, but it doesn't hold anything. If that gasket gets old and cracks- from today's terrible ethanol fuels- it's not available from Mikuni, and it'll never run just right. Unless someone starts making that gasket, it's carb replacement time.
Interesting comment on the carb, only other person I found who had this similar issue went through the same stuff I did, replaced the carb and that fixed it. I'll tear it back off and check that too
Paw Paw
FWIW here's a link to another thread (With Video), guy has same issue and replacing carb solved it. https://thumpertalk.com/forums/topic/945491-2003-rm-125-hesitation-vide…
I will shoot Ron an email asking about this metering block gasket.
Thanks!!
Now the question is...Do I pull the trigger on an eBay carb.
http://shop.discounthondaparts.com/fiche_section_detail.asp?section=845…
You.
Are.
Awesome.
Thank you!
Got the gasket on order at the local Ski Doo shop, should be here by the end of the week and I will post how it goes.
Digger - I'm originally from central NY (Finger lakes-ish), next time I'm in the area I owe you a beer.
Marko, I hope that solves the problems you are having with your co-workers bike. I feel your frustration. BTW, I live on the eastern side of NY, just above Albany, but am very familiar with central NY. I have been racing HS in WNYOA for over 20 years, and love it out there.
But it is still stuttering just a hair...I'm baffled at this point. Not sure what to do honestly. Stupid RM!
Pit Row
1. While riding and stuttering is happening can you slightly pull choke open and see if it changes or stops.
2. While riding and stuttering is happening can you put two rags over air filter and see if it changes or stops.
I am trying to figure out if you're lean or rich, or is the piston/spark plug is causing this issue. I need test results first.
Lastly, pull plug cap off spark plug and set in on the plug lightly, but enough so it won't fall off when you test it, this will slightly change the spark and might give you another clue.
I've seen the stutter when someone accidentally used a piston that was 2mm lower from TDC then the correct one.
You checked the piston to head clearance I suppose after this head was cut?
Speed_racer, I opened the choke once while testing it, bike bogged right down like it was super rich, I did not double check the squish after the head was cut, but I could do that tomorrow as well.
hey man know it been a long time was wondering if you found it out i have the same problem and can seem to figure it out did you sell it or fix it
His problems where 100% jetting related.
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