GPX Kickstart mod to solve kickback

[SnItChY]

Ok Chaps here's a lil tip for the yx gpx owners out there to solve the very painfull kickback

heres how pitsterpro do it and i just did the same

Pitster Pro Forum - View topic - Flywheel Mod for reducing Kick Back

my pics

stock flywheel picup

my puller

modded pickup

vid of how it was to start
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now a vid of the modded flywheel yea baby

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[rumble]

any idea on what that actually does, grinding the pickup?

 

[DvDRip]

my guess is it ******* the timing a little bit making it fire a little later.

thanks snitchy this might help when I get my yx150

 

[ando]

snitch mate have you found the need to retune since the mod?? i'd imagine a small change in the timing would change the performance somewhere in the power range? also noticed you didnt go quite as far as the pitster link what was the final measurement you went down to?

gotta say awesome find there too mate just started to find a bit of kickback on my yx150 since i upgraded my carb from the old standard vert125 carb to a new molkt (24 or 26mm not sure actually ) and since i've also changed out the stock yx IRK so this might end up being VERY helpful... we'll see once i got the thing properly tuned up by the 'guru'

 

[Dreadful]

Nice good find champ

 

[Cactus Jack]

You've done a good job SnItChY ... But technically you should get the flywheel rebalanced or at least spun up on a balancing machine to check ... You don't have to feel vibrations for damage to be occurring ... ie uneven wear to the LHS main bearing or fatiguing of the LHS crank arm ... Notice how Pitster covers their own ass by basically stating to do the mod at your own risk ...

Here's another XY150/160 quick fix ... with comments by that "annoying" mullet headed bogan Patrick Farsole ...

Solved Kick-back & hard start on my YX 160 - Planet Minis

 

[SnItChY]

yes i was thinking this also jack but as its in my zed i dont rev the tits of this motor ,so i was hopeing the less weight wouldnt affect to much but anyways i had to sort the kickback man it was crazy

i saw the other mod also jack and am going to do this as well ,then put a light on it and see where im at

the bike runs alot better now idels smooth and didnt loose any top end power so here's hopeing it all goes well

at the end of the day if it craps it sellf im going to go a lifan 150

 

[JHZ]

Just tried this on my GPX 125. It worked like a charm on the kickback starting problem, but now I seem to be having some performance trouble at high-revs. I tried this with a spare flywheel so I'm not sure if it's a difference in the flywheels or something else. I'm a bit reluctant to try it with the other flywheel without knowing the reason for it. Any suggestions?

 

[DvDRip]

line the flywheels up on top of each other, if the pickup and keyway are in the same place then it won't be the different flywheel, by cutting the pickup down you are retarding the timing and effects ALL of the rev range..... your best bet is to get a REAL ORK which has adjustable timing


and snitchy I'm surprised no-one else has picked up on this yet.... you're no starting it properly, you might have been fine if you just started from after TDC in the first place ?

 

[thump*140]

^^^ depends on the motor... Lifan 140's are meant to have kickback issues, yet i can flail away at the kickstarter on mine regardless of the engine position... never kicks back, even with a bit of throttle..

 

[DvDRip]

yea I've found the lifan 140 hardly ever kicks back and the yx140 loves doing it, but the yx140 won't kickback if kicked properly and I'm pretty sure snitchys wouldn't have kicked back either

 

[thump*140]

wonder if it's stroke/bore related, or purely ignition timing that makes the difference between the Lifan and YX's kicking back... ie Lifan stator and flywheel on a YX... although mine never kicked back with the stock stator, or the IRK... and i noticed Satchy's YX kick back like a mofo at the ride day, with an IRK... am guessing it aint just timing related...

 

[DvDRip]

I doubt it has anything to do with ignition timing, line up a yx and lifan flywheel, the only difference is the color. the YX does have off center cam timing which can't be corrected tho.

 

[tormentandglory]

Compression ratio makes a big difference to kick back, and being tuned right helps a bit. Longer stroke motors will kick back worse than short stroke motors.

 

[SnItChY]

yea man it kicked back like a ***** , now its sitting on a motor stand lol

i bent a valve so replaced them and am yet to restart the motor , i will 1 day im just lazy

 

[tormentandglory]

If you know how to dial in a cam properly, check the cam timing. China's are always out by a few degrees, usually more than a few degrees. That'll be an improvement to.

 

[Cactus Jack]

It IS the ignition timing 100% guaranteed ... no engine can kick back unless the charge is being ignited and reaching full flash point BEFORE the piston has reached TDC ... at which point it wants to go DOWN the bore ... so if the crank isn't swinging past TDC when the maxima bang bang happens ... The crank has NO choice but to reverse direction ...

If the knuckle head on the end of the kick start lever keeps pushing hard against the explosion ... something has got to give ... and it's usually a gear OR the case splitting ... Other unforseen damage can also occur such as cam chain back lash being taken up ... causing the piston to hit the intake valve and bend it ...

Cam chain tensioners are designed to work only when the crank spins in the proper direction ... just like the tensioning mech on bicycle derailleur gears ... A stretched cam chain could possibly even jump a tooth during a kick back ... Basically ... Auto tensioners don't work in reverse ... The drive side maintains cam degreeing but in reverse ... the cam degreeing can go out ... maybe the clowns at YX have offset the timing mark to allow for timing alterations when their engines kick back rather than solving the kick back problem in the first place ... from what Dvdrip says , they've fitted stronger kicker gears ... that reeks of bodgy engineering skills ... ie if their kids kept smacking their heads on the tops of the door ways in their house and splitting their head open ... they'd fit them with a solid steel helmet instead of simply raising the height of the door ways ... LOL ... An ounce of prevention is better than 50 billion tons of cure ...

The stress of the piston being made to deal with an unnatural amount of load during a kick back can also damage it so that it shatters at high revs ... and the big end bearing can also be over stressed ... And who knows if the force doesn't flex the crap out of the crank enough to cock or twist the two halves so that the crank arms run out ... leading to the crank snapping down the line ...

I've said it before and I'll say it again ... Kick back is worse than most people might think ... It is abnormal and damaging ... ON ANY ENGINE ... Even if it's a formula 1 motor built from super mega fugly titanium di-coxide kryptonite ...

Lifan 140's have an anti kickback mech on their cam ... but with mass production manufacturing , you're bound to get an engine (especially a factory untested crate motor) that kicks back due to the mech not being set right to the designers specs ... the key way on the crank might be out slightly ... enough to cause over advance and the flywheel key way to pickup tab might be out slightly too to compound the problem ... so it all adds up ...

In a nutshell ... it's quite naive and even laughable to not bother checking the initial and overall advance of your new engines timing against known to be accurate timing marks ... using a timing light ...

YX140's have a bigger cam with the AK mech removed ... so they have zero anti kick back protection other than possible compression bleed off ...

Compression affects the rate of burn of the cylinder charge ... so with higher compression the stock timing will be too advanced at kick start cranking speeds ... one way to get around that fact is to either lower the static compression on start up ... OR back the ignition timing off ...

Ignition timing and advance curve rates are a major part of tuning any motor ... even MORE important than jetting ... especially for a high performance motor ...

 

[sean01]

^^^^
i have a yx140 engine with factory decomp mech on the cam... the engine was advertised as having a larger cam fitted from factory..

lol it worked when it wanted to cause sometimes youd kick it and swear someone removed your rings...

 

[Cactus Jack]

They must have put them back on ...

The first YX140's that had IRK's as stock were'nt supposed to have the AK mech ... Motovert were the first to sell them in Aus ... They were "claimed" to produce 1.5 to 2 more HP than Lifan 140's ...

Maybe YX is putting smaller cams in 'em now ... But still saying they've got the bigger cam in 'em ?

The standard type AK mechs usually don't work very well on higher lift cams ... so they leave them out ...

Stomp Racing (Ooracing) is still trying flog the cams off cheap ...

OORacing - performance monkey bike, pit bike, madass, zoomer, dirt bike components - YX140 Cam Shaft (Powered by CubeCart)

 

[DvDRip]

yea my stock yx140 had AK mech,
And I completely agree with you about the stronger gears, they just beefed them up so the kickbacks wouldn't cause as much damage, instead of actually fixing the problem. The yx140 can kickback all day and only noticeable signs of damage will be your ouchy ankle lol
Lifan 140 with the smaller kickstart gears can only take so much kickback until they smash.... but at the same time they don't kickback nearly as easily as a yx140 in my experience.

But at the end of the day if you kickstart either motor properly, they will not kickback. Some clown on planet minis said that correct starting procedure only lessens the chances of serious damage in the case of a kickback and doesn't actually prevent the kickback. This is horse sh!t, kicking from just after TDC allows the crank and flywheel to build up a good momentum that will carry the engines rotation and push through the firing stroke with enough speed and power to keep it going the right direction and not allow it to fire backwards.
The way snitchy kicks in the vids looks to me like he gets the engine sitting just before TDC then kicks, so he's kicking it straight into the firing line with no momentum on the crank, guaranteed to kickback 1/2 the time on any stock yx motor that I've dealt with