bike runing fine 1 day and spluttering the next???

[Tomjoske]

I come to this forum once again with a technical question! So my 125cc tdr pitbike was finally running fine and pulling hard! the next day I took it out all of a sudden it starts popping and spluttering, lose power etc but only at full throttle it runs fine 1/4 - 3/4.. I understand this comes down to the main jet but why would it be running fine 1 day and then terrible the next???

 

[Tomjoske]

I took the carby apart and it's nice and clean and free from any blockage

 

[Tomjoske]

I also changed spark plug

 

[tono18]

have you done you valve clearances mate? 80% of bike need it doing after 1st ride

 

[my67xr]

yeah, i would adjust your valve clearances first, then look for vacuum leaks,
and check your exhaust nuts are tight at the bottom of the head.

[video=youtube;QJciyJRJh8Q]http://www.youtube.com/watch?v=QJciyJRJh8Q[/video]

 

[Tomjoske]

Ah ok didn't realise the valves could have that effect. Am I able to do it without the feeler gauges?

 

[Blender]

nah mate, feeler gauges are a must to do valves properly, there only about 5 bucks from supercheap auto.

 

[my67xr]

nah not really, if you have adjusted pitbike valves a lot i guess you could set them up close.
a set of feeler gauges will cost you about $14 from supercheap
or most auto parts shops sell cheaper ones too, you dont need to get expensive ones

 

[my67xr]

once you have set the valve clearances, start the bike and let it warm up.
keep it running, and spray some wd40/degreaser or carby cleaner on all the joins, eg carby to fuel bowl, carby to spacer, spacer to manifold, manifold to head.
if the idle changes in any way when you are spraying it, then you have a vacuum leak there that needs fixing.

 

[Tomjoske]

Checked for air leaks it's sealed up nice. Will try and get some feeler gauges tomorrow. It's just weird how it was running great 1 day and **** the next