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'01 RM125 fuel/air tuning

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Fixing up and tuning my neighbors rm125, he's away at uni, and I've got down time asides from work.

 

This bike is brutal. Needs a tone of cosmetic work, but the top ends OK, but bottom end might need a rebuild soon (not doing that for him lol). Had the carb apart, real easy banger stuff, but trying to tune the air screw. Is it like a thumper, in the sense you start from 0 on the thread and slowly crack it open? Trying to sort out the fuel mix being thrown in, seems a little lean.

 

No manual for this bike! All my handiwork and common sense, and ur guys insight!

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In general, 

on a 4-stroke it's a FUEL screw, to more you open/counter clockwise the richer the setting

on a 2-stroke it's an AIR screw, to more you open/counter clockwise, the leaner the setting.

 

Between 1-1/2 to 2-1/2 turns out is about the average range for an AIR screw.

Start at 2 turns out, warm up & ride the bike, then re-adjust for highest idle / best throttle response.

 

But before any fine tuning attempts, make sure the jets are clean and float / fuel level is set.

 

If you have doubts on the bottom end's condition, worn/leaky crank seals may add more variables.

(air or oil injested into crankcase)

Edited by mlatour

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In general, 
on a 4-stroke it's a FUEL screw, to more you open/counter clockwise the richer the setting
on a 2-stroke it's an AIR screw, to more you open/counter clockwise, the leaner the setting.
 
Between 1-1/2 to 2-1/2 turns out is about the average range for an AIR screw.
Start at 2 turns out, warm up & ride the bike, then re-adjust for highest idle / best throttle response.
 
But before any fine tuning attempts, make sure the jets are clean and float / fuel level is set.
 
If you have doubts on the bottom end's condition, worn/leaky crank seals may add more variables.
(air or oil injested into crankcase)

Yeah I've done a lot of work on 4ts, had a yz250f, it's fuel screw fell out so it ran really hot and lean, till I replaced it with a torc1 fuel screw. Im gonna get some fine tuning in today, it needed a new kicker, and shifter so hopefully it'll get going. Plastics are awful everything needs some TLC:)

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2 hours ago, Mr.mudman112 said:


Yeah I've done a lot of work on 4ts, had a yz250f, it's fuel screw fell out so it ran really hot and lean, till I replaced it with a torc1 fuel screw. Im gonna get some fine tuning in today, it needed a new kicker, and shifter so hopefully it'll get going. Plastics are awful everything needs some TLC:)

And once you get it running, everything that goes wrong with it in the next 2 years will be blamed on you by the neighbor because you "f***ed it up while you was messing with it". Recommendation.. Don't ever try to help someone who is "away at whatever" (translate.. too lazy to do it themselves).

Sorry for the negativity, but I've seen, and experienced, the end result of such helpfulness all too many times in the past..

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And once you get it running, everything that goes wrong with it in the next 2 years will be blamed on you by the neighbor because you "f***ed it up while you was messing with it". Recommendation.. Don't ever try to help someone who is "away at whatever" (translate.. too lazy to do it themselves).
Sorry for the negativity, but I've seen, and experienced, the end result of such helpfulness all too many times in the past..

I fully understand where your coming from. The bike, being In such bad condition, really can't get much worse lol, I may end up offering to buy it off him, he's never home and no time to fix it himself.

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Big issue: When bikes Idling in neutral, it runs fine, but as soon as you pull the clutch and whack her down to first, it stalls and lurches forwards. Already had whole clutch assembly apart asides from the separator rod. All plates and discs cleaned. What could cause this? Already fiddled with the actually line too.

 

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Check for warped clutch disc/plates, and especially for a notched basket.

 

More prone to lurch with thicker lube (15W-40) versus say ATF

when engine/gearbox isn't yet up to operating temp.

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