125cc won’t fire

[Bruces]

That’s on the low side for sure

[OneLeggedRider]

Look were your marks are, that's reading 97. 100 is really poor compression and anything 110 or below I'd recommend a rebuild.

[Nicthegreat420]

So anything below 110 is bad and needs to be looked into ? Timing chain removed and the rockers removed and valves removed, as well as the head, the head gasket, the piston the rod and shaft pin and clips. And leave the chain in the engine right?

[bogieboy]

if you have 97psi, it should at least pop off on a splash of fuel or ether down the carb... when i got my Roketa DB07A, it had siezed rings, and only made 67psi, but would cough on gas down the carb... i have seen engine run with 80psi like theres nothing wrong. however, after i put a new piston and ring set in my roketa, i made 170psi, and it runs like a raped ape....

for giggles, to verify, you are holding the throttle open when dong the compression test correct? you will get inaccurate readings with the throttle closed.

also, your valve lah will be fin at .05mm on both the intake and exhaust, that is still a fairly tight tolerance, .05mm is .002", most of the engines i work on (lawn mower mechanic) are .004-.013", so between double and far greater the lash. on my bike i have always set them by feel, tighten til theres no lash, then back off till you feel just a slight tick. if you cant feel the tick, its too tight.

[Bruces]

That sounds about right ,at a minimum ,but who knows what’s up with the crank bearings ,crank and the rest of the bottom end and transmission .Yes you can buy a top end kit pretty cheap ,but the chineese components have been hit or miss ,and more often than not a miss and the engines start smoking within a few weeks of doing the job .I guess I am saying to look into another engine complete ,and since yours is a street bike I think , I wouldn’t even consider anything else .

[China Rider 27]

Originally Posted by bogieboy

if you have 97psi, it should at least pop off on a splash of fuel or ether down the carb... when i got my Roketa DB07A, it had siezed rings, and only made 67psi, but would cough on gas down the carb....

I would believe it should cough too. Be nice if you would describe exactly what it does when you spray ether in the manifold? Does it fire at all, fire once, fire twice, 3 times, no fire at all, exactly what happens? I am not convinced this motor is getting good spark at the right time?

[franque]

Same here. I'd verify the flywheel position in relation to the timing marks before replacing the top end.

The light on the CDI doesn't mean anything, pull the plug, put the cap back on it, ground the plug and crank it over.

If both the crank and cam are off because of the flywheel being in the wrong place, it could give lower compression readings.

Check the timing with the piston stop before you buy anything. Also, ether will run on an engine with that sort of compression, unless timing was way off. It could also be that your CDI doesn't have good timing at idle.

[Nicthegreat420]

Doesn’t fire at all, coughs and sometimes spits fluid out the air filter side of carb.
Has spark but won’t ignite the vapor air mix to explode to
Idle.
Have gaskets ready for top end.
Q: what is a piston stop?
Yeah every time I brought gas directly into the spark hole and the intake, it would cough but never catch.. not
Booms.. no idling at all. I have a engine I could swap heads and all those parts on, and I have enough mula rn to
Buy a 190cc 5 speed n bolt it up. Just really tempted to take this engine into a garage and just take the top end off and examine the motor.
It has the carb gasket on, and the mechanic who came over a few times always would try starting the bike both full choke and doing all kinds of things, all
Good things like WOT starting, using the palm to choke the air intake, and using starting fluid. Never made any different sound with choke on or off, WOT, AND SPRAYING FLUID Didn’t make it fire up either. I’m starting to think I burn a valve or a ring ? Once I get home I’ll pull the flywheel cover off and again take a good readuling from it, I do know the flywheel is right and isn’t loose at all, is balanced and is the same flywheel with this bike it came with.


Main conclusion is the previous owner went HARD on this engine with out the ODOMETER running and basically trashed the motor, clicked it back up to the ODO, and ran it for 200 miles before selling it “as is” ... probably bought a motor that was predestined to die early ?

[franque]

https://lmgtfy.com/?q=what+is+a+piston+stop

[China Rider 27]

All the symptoms consistent with weak spark and/or mechanical timing issue and/or electronic timing issue. I never seen a cdi with a green light on it. I would follow Franque's advice.

[Nicthegreat420]

Alright I’ll check the piston stop, and check the flywheel again, and adjust the sensor and make sure it’s solid in relation to the timing and I’ll check again with the spark —I want blue spark over yellow.
Battery is fully charged again. I wish I could post my videos of the asselmbing of the stator flywheel ect.

This is my cheap cdi. Has a LES light on others end. Shows when current is flowing Out.

[bogieboy]

Originally Posted by Nicthegreat420

Main conclusion is the previous owner went HARD on this engine with out the ODOMETER running and basically trashed the motor, clicked it back up to the ODO, and ran it for 200 miles before selling it “as is” ... probably bought a motor that was predestined to die early ?

i would dare say never changed the shipping oil out. thats what happened with my bike, its too thin to be run for any length of time, and will cause issues in short order. my bike showed 250 mi on the odometer when i bought it.

[bogieboy]

Originally Posted by Nicthegreat420

Alright I’ll check the piston stop, and check the flywheel again, and adjust the sensor and make sure it’s solid in relation to the timing and I’ll check again with the spark —I want blue spark over yellow.
Battery is fully charged again. I wish I could post my videos of the asselmbing of the stator flywheel ect.

This is my cheap cdi. Has a LES light on others end. Shows when current is flowing Out.

probably not the issue, but i got one of those for my Roketa, and it would NOT start with the E starter at all due to the change in timing. you had to kick it over good anad hard and fast to get it to go, so i plugged the stock cdi back in and have been trouble free ever since. food for thought.

[Nicthegreat420]

So when I first got the bike it had the red T bolt CDI.
When I got the new motor I am mediately took the oil out after leaving the engine in the complete sun light 6 to 8 hours while I was at work came back home and drain the oil and put new oil in.
I can always go to a hardware parts store for this bike size and try and find a CDI that I can get the same day.
I was told that I could use a long screwdriver for a piston stop if I sharpie markers when it was at bottom dead center and top dead center, Will this work?
And a question that I asked earlier when you were cranking the fly wheel counterclockwise you are going with the natural flow of the engine and when you move the crank on the fly wheel clockwise you have the potential to mess up the timing. Yes or No?

[Nicthegreat420]

How do I post videos ?