Weird Hard To Start Problem??

[Zirtech]

hi guys just whacked a new yx140cc in my pitty

used all same running gear as lifan 140cc that was in previously

its really a massive pain to start!!!!

sometimes if i pump the throttle 20 times then kick it ..it might go

other times it wont start unless throttle is closed...

once its running the choke seems completely useless whether its up or down makes no difference...i doubt it would ever start with choke closed though

some times can be first kick...other times will need 30minutes of kicking to get it to go

spark is there and strong
rides fantastic once its going
ive disassembled carby and cleaned
used to start fine with old motor

adjusted valves and double checked...they are great...has heaps of compression

all i did is swap the carby to the new motor

any ideas?

 

[corey58]

your vavles need done

 

[Zirtech]

NOPE

should have mentioned....has HEAPS of compression and ive done valves

then rechecked again....they are perfect

 

[Custom]

Spark plug might be failing, open the gap up to about 8x what you run at and see if it still sparks ( larger gap simulates compresion) Or the carb might have a bit of gunk floating around that was disloged during the swap over

 

[Zirtech]

i cleaned carb out and blew the whole thing out...being brand new its in great condition especially after clean

as i said when it finally starts it runs VERY VERY VERY well!

 

[pickles09]

my yz 140 is like that u get the knak of starting it sumtimes it floods sumtimes first kick

they have a mind of there own

 

[Zirtech]

hahahaha
i wish i could find a knack for mine....it just seems to do whatever the hell it wants


then occasionally ill kick it and it will blow a flame a foot long

 

[Panda_ET]

my 140 tho its a lifan has the same kind of issue, the low speed jet is too small and its too lean i havent got round to upgrading it yet.
you can tlel mines lean while it idling it pops and farts a fair amount and wont idle smoothly till its warm

 

[Cactus Jack]

my 140 tho its a lifan has the same kind of issue, the low speed jet is too small and its too lean i havent got round to upgrading it yet.
you can tlel mines lean while it idling it pops and farts a fair amount and wont idle smoothly till its warm

Some info that may help ... Valve seats can distort slightly and allow gas to flame back thru the intake manifold which shows up as hiccing and popping when cold (pressure leak) ... The leak can go away as the engine warms up and the valve seat expands ... allowing a better seal ... The valve clearances can be spot on too ... You can only detect the lack of seal at the seat by checking with bearing blue (Prussian blue)

[A bit of trivia for you ... Since you know so much about turbos ... you should know that the above fact is why the heads of top fuel cars are completely stripped and the valves inspected and replaced with new ones if necessary , then every one of them is hand lapped and checked for a perfect seal before being reassembled in the head and put back on the engine for the next race ... This is done while other crew members completely strip , inspect and rebuild the rest of the engine ... If there is the SLIGHTEST pressure leak thru an intake valve the engine won't merely hic or pop ... the compressed fuel charge in the blower will explode like a bomb and blow it off the top of the engine ... It'll rip bolts and threads clean out of the intake manifold and even break parts off it ... That's why they have blower restraint belts , a scatter blanket , and use special hollow alloy studs that are designed to let go at a lower breaking strain than the blower housing and manifold ... ]

http://www.miniriders.com.au/forum/tech-talk/12162-engine-troubles-2.html

http://www.miniriders.com.au/forum/tech-talk/15814-140cc-lifan-head-making-noises.html

http://www.miniriders.com.au/forum/tech-talk/16154-bike-wont-start.html

 

[Panda_ET]

we getting touchy here??
anyway Im starting with the easiest option since it was like it from new, if it doesnt get better then i will strip it down. or just chuck it away its just a china lol

 

[pickles09]

or instead of chucking it away give it to me for 50 buks hehehe

 

[Panda_ET]

only if you come pick it up pickles

 

[Zirtech]

its weird...i can kick it correctly 20 times...and it wont even sound close to starting..not even a single sound of combustion

then out of no where it comes alive

sometimes flooding it works...other times no throttle at all will work

 

[muzza24]

hey have u checked the air n fuel mixture is right? mayb u will have to play with the screw for that good luck muzz

 

[Zirtech]

i thought of that...but it runs so dam well when its running i didnt wanna wreck how well it ran by changing it

 

[coolmodee01]

check that your coil is earthed properly

this will cause an intermintant spark or none at all

after that cdi but i'd doubt it

but i reckon cuctus is on the money we had a similar thin on a yx motor turned out to be a bent zorst valve so no sealing and sticky open

good luck

 

[Zirtech]

has heaps of compression

with the coil/cdi thing....the thing is... its ONLY hard to start...it never stalls ever and goes unreal!....its just when its stopped...it may kick first time or it may take 30minutes

hot or cold doesnt matter its the same either way

 

[Zirtech]

UPDATE

just advanced the timing a bit and seems to be starting better now

 

[Panda_ET]

yeh just fixed mine as well lol, the jet had a tiny amount of build up all around the hole making it look fine but the hole was too small. I havent had much to do with carbies so its a bit new to me Ive previously only used programmable ecu's. Live and learn very happy with outcome tho

 

[Zirtech]

which JET? theres 2