XR75 wont start

[Vince H]

hey guys been doing a part resto on my XR75 but cant get it to fire has spark fuel and compression can anyone help me out with what might be wrong   even tried start u bastard cheers

[frostype400]

You don't have something blocking off air to the carby rag in airbox? if you have spark it would fire if you have fuel but you need air maybe your timing is right out?

[Slakewell]

180 out on the cam?

[Vince H]

no there's nothing blocking the carby that i know of. also have gone over the timing twice myself and had a mate look at it that knows more about bikes than i do and still wont go any other ideas

[Hardex]

Check you key way on the crank shaft behind the flywheel ,that it hasn't back fired and partly cut the keyway in half.This is a common problem as you still get spark but your about 20 Deg out on your timing.

[Tim754]

It has some but how much compression??  bent  or non seating valve, still check the flywheel key as Hardex has answered first, agree they can cause grief in the baby XR's

[smed]

non seating valve,

The most common problem on small Honda 4t's ,check inlet valve clearance

[sleepy]

Try a new spark plug and fresh fuel.

[pancho]

Birds nest in the exhaust pipe??

[80-85 husky]

wires wires wires....ol mate reassembled his xr 500 and spent two days kicking and re building the rebuild till he figured the coil wires were cross :oed. check the wires...

[Vince H]

Will check these ideas out can someone tell me how to check the inlet valve clearence exhaust is new so should have no blockages I can feel the compression with my finger over plug hole don't have a tester so can't tell exactly how much it has

[FourstrokeForever]

Will check these ideas out can someone tell me how to check the inlet valve clearence exhaust is new so should have no blockages I can feel the compression with my finger over plug hole don't have a tester so can't tell exactly how much it has

Get the piston to TDC. Both rockers (inlet and exhaust) should have some play at this point. Not sure on what the clearance is supposed to be but your manual will have that info. It's just a matter of loosening the nut at the rocker and adjusting the screw until the correct feeler gauge can move ever so slightly between the screw and valve tip. From memory, I think the gap should be 0.04"

[Tim754]

 0.04" both valves    cold.

[Vince H]

Well checked what has been mentioned and all seems to be fine but now I'm not getting spark at the plug and the spark I can get by disconnecting the wire to the coil and hold it against the motor only throws an orange spark now instead of a bright blue like before. Side as has been off while sitting around for couple of days could it be some rust starting to form on the magneto ?

[sleepy]

Maybe it is time you told us all about what has been done to the bike since it last ran or did you buy it not running.
Most of what has been suggested won't happen to a bike just sitting for 6 months.
Does an XR75 have pionts? If there is no spark make sure the pionts are clean.