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rm125 upgrades


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Hi my name is Brandon. I just bought my first bike since I was 16, it is an RM125. I am an intermediate rider that does mostly trails, oh yeah I am also 6'3 275lbs in street clothes. I wanted a 250 but i bought this cheap thinking it needed a top end but it needed a bottom end too, so the motor will be fresh. It's all stock with a dented to hell pipe, some sort of carbon reeds and an aftermarket air filter. What do you think some starter upgrades should be?

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if the bike needed a top end, bottom end, and a dented pipe, I'd say the bike might not have been taken care of to begin with, and will need a lot of corrective maintenance first, then basic maintenance, then upgrades last

you can nickel and dime your way around maintenance by reading the forums, but a great start is just to pick up a clymer service manual...it's honestly such good reading you'll sit on the toilet for hours trying to learn it all

clean and adjust the chain/sprockets (replace if necessary), adjust the clutch (replace parts if slipping or gripping), change the transmission fluid, check your coolant level/hoses, inspect your front/rear pads/rotors/brake fluid level, clean the air filter, inspect the spark plug, inspect/replace the fuel line, inspect/replace control cables, check for bent wheels, spoke tension, worn tires, inspect axles for run out/lube, adjust the tire pressure, check your fork seals (adjust oil level, equalize pressure), check the rear shock bearing, check the lower linkage pivot bearings, inspect all fasteners, inspect the swing arm bearings, check your exhaust valve, repack your muffler, inspect/lube the steering head bearings, adjust the brake/throttle free play, clean the carb, adjust the float, jet it for your altitude/temperature, tear down the motor and look around (top end/bottom end/reeds, etc.), so there's a start!

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if the bike needed a top end, bottom end, and a dented pipe, I'd say the bike might not have been taken care of to begin with, and will need a lot of corrective maintenance first, then basic maintenance, then upgrades last

you can nickel and dime your way around maintenance by reading the forums, but a great start is just to pick up a clymer service manual...it's honestly such good reading you'll sit on the toilet for hours trying to learn it all

clean and adjust the chain/sprockets (replace if necessary), adjust the clutch (replace parts if slipping or gripping), change the transmission fluid, check your coolant level/hoses, inspect your front/rear pads/rotors/brake fluid level, clean the air filter, inspect the spark plug, inspect/replace the fuel line, inspect/replace control cables, check for bent wheels, spoke tension, worn tires, inspect axles for run out/lube, adjust the tire pressure, check your fork seals (adjust oil level, equalize pressure), check the rear shock bearing, check the lower linkage pivot bearings, inspect all fasteners, inspect the swing arm bearings, check your exhaust valve, repack your muffler, inspect/lube the steering head bearings, adjust the brake/throttle free play, clean the carb, adjust the float, jet it for your altitude/temperature, tear down the motor and look around (top end/bottom end/reeds, etc.), so there's a start!

All the fluids will be changed since I drained them out to do the motor as well as a new air filter. I will take care of all the repairs and maintenance before I ride the bike. I have done/am doing most of them while I've been waiting to get the crank back from the dealer. Thanks a ton for the advice.

I am looking more for advice that will get this thing to haul my heavy ass around a bit better.

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I am looking more for advice that will get this thing to haul my heavy ass around a bit better.

Gearing 👍

If still running stock size sprockets, going up a tooth or two on the rear will help with the extra weight. A tall seat would help with your height a little.

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ahh, I see...you probably got most of what I mentioned covered

assuming the bike is maintained, I would next go for tuning and adjustment for your weight: adjust the pre-load in the rear to get the right amount of sag, then set the rebound and dampening to your riding preferences based on the trails or MX track (some people like more, some like less, start at stock and see where it takes you)...note that if you do weigh more than what the stock suspension can do, you might need to get some higher rate springs for the front and back. Note, that if you're using a stock MX bike on trails, it would also help to get the forks and shock re-valve them (could run ~$750)

(I'm still relatively new at this, but) after that I don't that think there will be a whole lot you can do for power if you've already replaced the top end and bottom end. For more power, just get a 250.

The next step, if you were to keep this bike, would be to replace or bore out the cylinder to a larger displacement (ie. 144/150cc), get a crank with more throw, ported, a full exhaust (and jetted to compensate for the increased air) and go -1 on on the front sprocket and +2 to +3 on the rear to get some more lower-rpm oomph

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From the reading I have done I think I will get a bigger rear sprocket, stiffen up the suspension, and I'm working on getting an fmf for it. I am basically just looking at getting by until this sells. I bought it for cheap and should make some money on the sale so I can pick up a 250.

Thanks guys, keep the advice coming please.

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