valves??

[red_demon24]

hey guys having a problem with my ducar 125 motor it has lost alot of compression my dad says it may be that the inlet valve is stuck open a bit because it breaths back out through the carby and if this is the problem does anyone know what the tappet clearance is for the valves?
or if you have any other ideas what it may be doing could you please let me know cheers.

 

[tubes380]

its .003" for the inlet and .004" for the exhaust, works out to be nearly .07mm and .1mm in metric

 

[themountain]

copy that^^^^^or does it smoke when it runs??? busted rings maybe...or a blown headgasket...or the plug isn´t threaded right...lol

 

[red_demon24]

dosnt really smoke the plugs a bit black on the end though?? and the other day the spark plug didnt want to go back in easily and sorta got stuck half way and had to put a bit of preasure on it to tighten it up the thread was just a bit out of line. i asked my dad if it is the rings and he said no but havnt checked the head gasket though ill have a look at it.
if any one else has any idea's please let me know cheers.

 

[tubes380]

youll find its the valves, reset the clearances and the problem should go away, you might also wanna tune your carby as the black spark plug shows its running rich, tuning it will make a huge difference

 

[red_demon24]

do i tune it with the air mixture screw? and do i screw the screw in or out?

 

[motoXXX]

id go .003 for inlet and .005 for exhaust every one thats done that it works a treat its on mineand its flying

 

[tubes380]

yes thats fine too, as for tuning, try searching i posted a really good explanation in one of the threads telling you how to tune a bike properly, base line is the air screw, needle position, pilot and main jet sizes all affect the performance of the bike, and all need to be close to correct to get the max out of any bike

 

[Cactus Jack]

Yeah ...... do the valves FIRST and do them with both valves closed at TDC on the power stroke ("T" mark on flywheel aligned with index mark on case ... cam sprocket mark pointing towards front of bike) ...... then run it for a while and recheck the plug colour ... Always put a light coat of oil on your plug threads and put it in using your fingers only ...... if it gets tight do not force it using a spanner or there's a good chance you'll cross thread it and strip the thread ...... with the resultant consequences ..... head removal , heli coils and HEADACHES ......