did valve clearances, made my sons bike worse????

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gottagetacheaperhobby

gottagetacheaperhobby

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hey guys did my sons gpx 125 valve clearances today, started her up and it now wont rev past 1/4 throttle and is backfiring flat out.................. what the F*ck have i done?

i have tried a new coil on it as well, no change what so ever
 
Done the clearance too tight, or you had it 180 out when you did it
 
piston was tdc when i did em, and the magneto mark was lined up and the cam chain mark lined up to the dash at 9 0 clock on the casing..... i did em at .003 inlet and .005 exhaust..... if that is whats happened though would i have damaged the valves?
 
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Unlikley but possible, you will find out :p
Pretty much get the piston to tdc look at the rocker arms and rotate the engine by turning the flywheel...
then the rockers should not move for a long part of that rotation as so its not on the overlap
 
so i just double checked and did the clearances at .004 and .006 as per ooracing guide and its no better, it absolutely refuses to rev past 1/3 throttle. runs fine at idle and up to 1/3 throttle but past that it just breaks up back fires and carrys on. i cleaned the main jet out, no better checked for air leaks, got none, so what the hell is going on.... some one please help
 
Try one out of another bike 1st
what promt you to do the valve clearances?
did you try another cdi?
 
did you try retuning it after setting the clearances ?

what were they set at before you adjusted them ?
 
my67xr said:
did you try retuning it after setting the clearances ?

what were they set at before you adjusted them ?
Click to expand...

tried re tuning the carb, cleaned the carb out, no change

not sure what they were set at before i adjusted them as i just un screwed the tappet to get the gauge in there and then set it to the gauge (if you get what i mean, sorry a little pissed off atm)
 
did you inspect if the rocker arms moved immediately like i described in a earlier post?
the markings may be different on the 00Racings motor..
 
yeah there was free movement in the rocker arms when i had it set at tdc............ about a mm of up and down movement in them..... i have done the valve timing on a couple of bikes and never had a issue until now...
 
so the line on the flywheel was at 12 o'clock , when the cam gear was lined up at 9 o'clock ?
 
okay cool, if certain there is no air leaks then i'd say plug or coil or atleast have a look at the plug
also blow on carby at the back to be 100% sure there is no lips (give the bike a little tongue while your at it it might tickle a stronger fire)
 
yeah it was sounding a bit noisy before i did em, but this engine has been a little noisy since new. it was still running and revving freely tho whereas now as soon as you get above 1/3 throttle it just back fires pops and farts almost like its hitting the rev limiter

to be fair the 1mm of play in the rocker arms is a guess at best, would probably have been less than that
 
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when you adjusted the rockers with it all at tdc,
is the tab on the outside of the flywheel close to the pickup sensor ?
 
sorry for all the questions, just trying to think it all through
 
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