Valves should be set at .003"-.004"



Tear into the top end if that isn't helping and let us know what you need, we have parts



Also make sure your exhaust gasket is installed before you slip your pipe on (silver ring). That may be some of the cause for the backfiring and such.

 

It has a new exhaust gasket and new exhaust.

 

Ok 2 things out of the way, check the valves when the motor is cold and at TDC and then go from there.

 

Ok. I am a mechanic but i have never taken apart one of these 125cc motors. To measure the valve clearance do i just need to take off the 2 covers over the vales and check it with a feeler gauge? If so what should they be set at so i can adjust them?

 

Ok. I am a mechanic but i have never taken apart one of these 125cc motors. To measure the valve clearance do i just need to take off the 2 covers over the vales and check it with a feeler gauge? If so what should they be set at so i can adjust them?

Yes just take off the tappet covers and use a feeler gauge. Valves should be set at .003"-.004"

 

I just checked the valves and the intake was out of adjustment. The exhaust was fine. That took care of the ticking sound.



The motor just stops revving at 2500rpm and from then it just boggs but it will continue to go the same same speed. The bogg sound gets deeper as you turn the throttle more and at wide open throttle it just backfires.



I have adjusted the main jet in the carb but it makes absolutely no difference.

 

Try running the bike without the air filter. While the air filter is off check the throttle slider to make sure it is opening and closing all the way.

tmas

 

The slider works perfectly. I just went through the carb today and it was perfect. I pulled the plug and it is running a little rich but nothing that should effect it that much.

 

22 mm mikuni carb? Maybe check the engine compression, you will need a gage. Try a brand new plug make sure your air filter is not restricting it.

tmas

 

My carb is a 22mm sheng-wey. I have tried a different carb from a running motor, still has the same problem. I have tried a new spark plug and a CDI box from a running motor and checked all the grounds and wiring. I pulled the exhaust off to check to see if it was clogged but it is perfect. I am positive it is not a fuel problem as i have swapped a running carb on it. And i have run it without an air filter with both carbs. The only thing that i have not checked is the coil and the compression. If i rule those out then it is something internal.

 

motors timeing?

 

my 05 thumpstar is doing the exact same thing cleaned the carb and filter about 3 times already.... im gonna check all the grounds,and the sparkplug and maybe the vavles tomorrow if i get time...

 

Make sure you have the motor grounded correctly. Ground the ground wire to the frame and strip the paint where you ground it. A bad ground would make it run like that and sometimes it wouldent even run at all.

 

Yea it kind of does sound like the cam timing is off, maybe it jumped a tooth? Pull the ignition cover off and see if the timing marks line up.

 

It could be the timing but i dont know how to check the timing on these 125 motors. Is there a way to do it with a timing light? Is there a way to do it at all?



It might be the timing because it idles cold perfectly, might be advanced alot. And the motor gets worse every day.



How can i adjust the timing?

 

Today 07:18 PM

orraclekid15 Yea it kind of does sound like the cam timing is off, maybe it jumped a tooth? Pull the ignition cover off and see if the timing marks line up.



So check the marks on the flywheel and cam? How does the cam cover come off, just unscrew it?

 

There is a bolt on the opposite side of the head, directly across. Take that out and the cam cover will fall off. Then just line the t mark on the flywheel with the mark on the case and the mark on the cam sprocket should line up with the mark on the head. If not then you know the problem.

 

OK. Ill have to do that tomorrow. Thank you for your help.



Do you know how to check the ignition timing on the motor.

 

Ignition timing isnt adjustable unless you have an inner rotor kit so you should be all set there.

 

Alright, ill get back to you tomorrow after i compression test it and check the cam timing. Thanks again for your help.

 

ill give you 250 shipped for it.

 

Sounds like you've got the timing off or a bent exhaust valve. That's my guess...same problem I was having with another bike except I could get it to rev to 6k or so. Once it reached that, it was exactly what you described.

 

Check the coil... and ground.. i am keeping my fingers crossed that is not a bent valve... was the eng running well before and out of no where it started doing that??



my krappasaki quad was doing the same .. it was the a bad coil .. i hope its something easy ..don't give up!!!

 

I checked all the wiring everything is perfect. i will swap another running coil onto it today.



The motor is getting progressively worse. Every week it is slower and slower.



I am thinking it could possibly be a collapsed/broken valve spring.

 

I checked all the wiring everything is perfect. i will swap another running coil onto it today.



The motor is getting progressively worse. Every week it is slower and slower.



I am thinking it could possibly be a collapsed/broken valve spring.





Today 05:45 AM

motoman2003 ill give you 250 shipped for it.





I will take you up on that offer motoman2003 if i cannot fix it this weekend.