Bike losing POWER :( why?

Shop deals on ebay
Advertise with us
Find deals on amazon
Mini Dirt Bikes & Pit Bikes Forum

Help Support Mini Dirt Bikes & Pit Bikes Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
M

makedonski

Well-Known Member
Joined
Mar 17, 2009
Messages
60
Reaction score
2
i gotta yx140cc and lately it's feeling as if it is losing power. i think its because the time when i raced my mates 160 and i bet him i valve bounced it in 4th gear. it's about 10months old. oil always changed regularly.

i think it's because maybe i need a new piston and rings, gaskets, check valve clearances. It also idles incosistently. like it revs high for like 2min den slows down, i give it some throttle then it revs for another 2 min again.

Im afraid of the cost of fixing and wondering if its worth fixing or getting a new bike. $65 for an hour of labour plus parts. Please gimme some advice anyone.
 
Last edited:
How's the compression?

Check valves first:
- YouTube - How to check valve timin on Honda 50 70 cc motors
- QingQi (Qlink) 200GY Illustrated Valve Adjustment - MyChinaMoto - Chinese Motorcycle Forum
- http://www.miniriders.com.au/motor-tutorials/24965-how-set-valve-clearances-horizontal-engines.html

If then the biks is still low on compreesion it'll be the piston and rings. The reving is probily due to the carbi which can result in lack and/or loss of power. Pull it down and give it a clean:
- http://www.miniriders.com.au/carby-tuning/16270-carby-pull-down-rebuild-tutorial.html
- http://www.miniriders.com.au/carby-tuning/10183-mikuni-25mm-carbie-manual.html

I doubt it'll be your gaskets as you only need to replace them when you take the engine apart but try the valves first then the carbi.
 
Regarding the compression, i can still feel it when i kick but it doesn't kick back hurting my ankle like it used to. i wanna check the valve clearances myself but im worried i might stuff something up, i guess ill give it a try.

so at the most i would need a carby clean or new carby, new piston and rings, gaskets too just in case. ok. ill try the valve clearances first. thanks mate.:)

update: the valve clearances looks too complicated. ill probably try the carby clean if thats not too hard either.
 
Last edited:
I did a valve clearance! There really simple if you get the right tools! I reckon it's worth you learning a valve clearance! I am a 21 yr old female that over filled the oil in my car.. i have completely no idea when it comes to mechanical things.. yet I PULLED OFF A VALVE CLEARANCE!! There pretty easy once you got them in the right place. I pulled my motor out to do it to make it REAL simple!

Give it a shot... watch the videos and get the right tools!
 
yer i saw the vids now, it doesn't look too hard. i might give it a try.

update: the only part i don't get is when he moves the flywheel to some special position.
 
I did it at .004 and .006. but depends on ur bike. umm just make sure u do it the right way round ha ha!
 
.004mm for the top one and .006mm for the bottom one. and what do u mean the right way around lol.
 
like don't mess up which one u d as the 4 and the one u do as the 6... coz ur bike wont like it lol
 
set them at 0.003 and 0.004, it's the same for all small china engines.

it may look hard but it's VERY EASY, just do it you'll see how easy it is, and it's an impotant part of general maintenace that ALL THE noobs overlook.... and if your bike isn't running right then that's the first thing you should check
 
the revving high for 2mins sounds like you have a leaky intake manifold seal or dirty carby, but there's no point checking the seal and carby if the valve clearance hasn't been done FIRST!!!
 
makedonski, valve clearances are FAR less complicated than they look or sound... i've got them down to a fine art, and can have them done in under 8 minutes... and if a clumsy fat bastard such as myself can do it.. ha ha... seriously though, it's a far simpler process than you imagine... follow my thread on Valve clearance setting, and watch the vids, you'll ace it...
start with those, followed by cleaning the air filter, pulling down the carby and cleaning that... unless you are real hard on the motor, and flog the living bejesus out of it, i cant see you requiring a new set of pistons and rings just yet... :) good luck!!!
oh, and DVDrip is probably right about the idle... air leak around the carby manifold will probably be )the culprit... (Dvdrip one word from you about air leaks, and i'll ban your ass... ;))

Oh, and your valve clearances should be .003 for your intake, (closest to the carby) and .004 for the exhaust (closest to the exhaust, oddly enough...)
 
lol... I remember this one dude had a leaky carby and I toid him that was the case..... and THEN.......

:p
 
makedonski said:
.004mm for the top one and .006mm for the bottom one. and what do u mean the right way around lol.
Click to expand...

just have to point 1 thing out here...

the settings are .004 THOUfor inlet and .006 THOU for exhaust..

you keep speaking about millimeters and if you cross them over you will fark up...not that your likely to find .004/.006mm blade but it will stop your head from herting lol ;)

and ill back that up in regards to more than likely an air leak or sht in yr carb for the idle problem...
and how clean is yr air filter?
and dont forget to oil it too..

but yeah ya cant do 1 with out doing the other...the most important being valve clearances..

and thump lol so feel so bad, i had blonde moments too while tuning carbies... you get so lost in the tuning that ya end up missing the obvious..
 
Last edited:
yea we've all made some obvious mistake at some point that just makes ya feel a bit dumb hahah
 
When it kick start leaver comes back real hard it's called 'kickback' and thats due to not kicking the enigne from just past TDC (top dead centre) and 'kickback' can stuff your kickstart gears. Have a look at these:
- http://www.miniriders.com.au/motor-tutorials/25055-how-start-pit-bike-properly-top-dead-center.html
- http://www.miniriders.com.au/motor-tutorials/25024-how-replace-broken-kickstart-gears-video.html

Regarding the air leak I have no clue :eek:. Thats there domain but take a look through this for carbi tut:
- Carby & Tuning - Mini Dirt Bikes & Pit Bikes Forum

And set the valves at 0.003" (top) inlet and 0.004" outlet (bottom).

Goodluck.

Hay thump*140, sean01 and DvDRip one of you should make a symptoms thread invovleing carbies. Just a thought.
 
You must log in or register to reply here.

Latest posts

Back
Top