Problem starting Pit Pro 140cc

[MitchAustralia]

alright, thanks again mate.

 

[Cactus Jack]

Yep ... As Dvdrip states ... Do the valve clearances first (pulse waves from an intake valve leakage can make the intake charge too rich) ... Next , check the fuel level in the carbs float bowl as too high a level can cause flooding and a wet plug ... The float bowl fuel level also affects the mixture across the entire jetting range ...

After that adjust the mixture screw on the carb ... if it's underneath on the manifold side it's a FUEL screw ... so screwing it OUT richens up the mixture and screwing IN leans it out ...

How to adjust a fuel screw ...

ThumperFaq: MXA Fuel Screw

http://www.miniriders.com.au/tech-talk/13523-where-air-screw-mikuni-vm26.html

http://www.pitsterpro.com/uploads/docs/Set up_jetting made simple.jpg

If it's on the side of the carb near the air filter it's an air screw ... so screwing it IN richens up the mixture and screwing it OUT makes it leaner ...

Mikuni carburetor operation and tuning

Kick back is more likely to be caused by high compression combined with too much ignition advance ... Increasing the static compression ratio via a high comp piston , BBK , stroke increase etc can cause kick back even with the proper stock static advance ... Timing advance must be matched to the compression ratio and the octane of the fuel used ... Too lean a fuel/air mixture can also cause kick back and detonation ...

You can try retarding the ignition by moving the pickup anti clockwise clockwise ... you can also try running higher octane fuel (premium or race gas) ... Either way ... it's best to actually check the ignition timing with a stroboscopic timing light to see exactly where it's firing at ... (Inductive pickup power timing light) ...

There's some great info in this link which relates to IRK's and timing advance in relation to compression ratio ...

PENTON RACING PRODUCTS INC.

 

[DvDRip]

once again you deliver the good info cactus that fuel mix link is great
I was going by this one and it's pretty vague in comparison ThumperFaq: MXA Thumper's Fuel Screw

to get to the fuel mix screw I bought one of these:

CARBY MANIFOLD ENGINE ADAPTER ALLOY 26MM BLUE DIRTBIKE - eBay Other Makes, Bike Parts, Motorcycle Parts, Accessories, Cars, Bikes, Boats. (end time 27-Jul-09 18:19:01 AEST)
It was a 22mm so I had to grind it out to fit my intake port, and the countersunk bolts stuck up about .5mm so I had to grind out the slots too, now I can turn my carby out to the left and get a screwdriver onto the screw

 

[Pit Pro Girl]

yes you can get a decompression cam, not the easiest mod to do

MitchAustralia If it's been this long and you're still having the problem you need to take my original advice and remove the stator cover, that way you'll know you'r doing it right, I used to have the same problem with my 140 until I did this

take off the cover on the left of the engine, it's 3 small bolts, then it will look like this:

the brass coloured thing is your flywheel, it has a marking on it "T" & "F" when the T is at 12 oclock your engine is at TDC, it passes the mark twice when kicking over but one of these passes is the commpression stroke, you'll know it's the commpression stroke because it's hard to kick.
now turn the killswitch OFF and kick the bike over slowly while looking at the flywheel, you'll get to the commpression stroke and see the T mark come up to the top, now push it carefully until it just goes past 12oclock, now turn the killswitch back on and give the kickstart one good hard kick, if the bike kicks back doing it like this then there's something wrong with it, and if you don't wanna hurt your foot when you stuff up you should be wearing boots anyway

Where could I get one of those????? And are they expensive???????

 

[DvDRip]

you mean a decompression cam? don't ask me but someone else would know, try akunar or maybe dhz.
Snitchy made a thread a couple days ago on how to reduce kickback by shaving a bit off the flywheel, that was for a gpx 150 but it probably works for a yx140 too

 

[bulldog93]

what a great thread props to Snichty: http://www.miniriders.com.au/tech-talk/23730-gpx-kickstart-mod-solve-kickback.html

 

[Cactus Jack]

Pit Pro Girl ... Junior Member ... Where could I get one of those????? And are they expensive???????

What ? One of those pretty "Brass coloured things" ... LOL ...

They're a non adjustable stock flywheel ignition ... They make the bike easier to ride over an Inner rotor ignition ... but you can still cop kick back with them ...

A Lifan 150 ORK "Silver/chrome coloured thing" ... is in between ... They make the bike easier to ride , can be easily adjusted to eliminate kick back , and give increased acceleration over a "Brass coloured thing" ...