Hey I to change a values how I can't get compression on it now and do u no how to time it it is a Yamaha 1999 100hp 4 stroke

Do a compression test. The actual value is less important than all cylinders being within 10% of each other. I.E. if #1,2,3 are 110,115,112 psi and #4 is 98 psi, it's time for a rebuild.

Hey Alex, No, I would get a new bulb..check for leaks in the fuel system.

4 stroke --same as any engine ---140-160 psi
2 stroke 60 psi upwards

Sounds like you need an experienced motor mechanic

Set the piston to TDC (top dead center) this is the higest point the piston will rise before moving on to the down stroke, either by lining up the marks on the crank rotor or a long screw driver (large handle so it wont fall in) down the plug hole and watch for the highest point lock or hold at this point. If cam sprocket has marks line them with the cylinder head surface (sometimes the sprocket bolts) parallel.
The cams should be fitted next on the 'compression' stroke meaing the all valves should be closed when the cams are seated (no valves being pressed by cams) generally at this point the cam lobs face away from the valves , next stroke down (ignition of fuel) valves should be closed with the exhaust cam moving round ready to rock on to the exhaust valve as the piston rises to the top again (4th stroke exhaust) as the exhaust valve lobe rocks off the intake cam lobe should be starting to rock on opening the intake valve on the down stroke of the pistion.
Trun the engine over by hand to make sure no valves are knocking the piston.
Should be as follows
1. all valve clearance free/rocking at ' TDC 1st 'down' stroke (ignition of fuel) valves closed exhaust moving round but not pressing valve ,
2. 2nd stroke 'up' exhaust valve rocking open and closing as piston tops with the intake ready to rock on as the exhaust closes and piston tops (exhaust),
3.3rd stroke 'down' (intake of fuel) as the piston moves down the intake valve should be opening.
4. 4th stroke 'up' compression of fuel all valves rocking closed as the piston rises for the compression stroke back to TDC all valves closed/rocking free.

Intake, compression , ignition and exhaust. (**** squeeze bang blow)

check for any compression leak if no then change the piston rings.

2001 Yamaha YZ80 Specifications Engine Engine Type
2-stroke Displacement
83 cc Bore x Stroke
47 mm x 47 mm Compression Ratio
8.2:1 Engine Cooling
Liquid Carburetion Carburetor
26mm Mikuni Transmission Transmission
6 - speed Chassis Wheelbase
49.5 in Ground Clearance
13.7 in Seat Height
33.6 in Fuel Tank Capacity
1.3 gallons Forks Forks
33mm Kayaba Fork Travel
10.8 in Shock Shock(s)
Kayaba Shock Travel
11.1 in Wheels and Tires Front Wheel
17 in Rear Wheel
14 in Brakes
disk/disk Other Information Intended Use
Motocross Color Scheme
Blue Cost when new
$3199

Same happended to me with exactly the same motorcycle... I solved the provblem by replacing the crankshaft oil seal on the rightside of the crankcase. It solved the problem immediatly!

The horsepower of that mighty beast is exactly 100 horsepower (73.6 kW). Here's some of the other specs:

Engine Type - Air cooled, 4-stroke, V-twin engine, OHV, 4 valves

Displacement - 1,854 cc

Bore & stroke - 100 x 118 mm

Compression Ratio - 9.5:1

Max. power - 73.60 kW (100 HP) @ 4,250 rpm

Max. torque - 167.80 Nm (17.1 kg-m) @ 2,500 rpm

The two most important aspects of four-stroke maintenance are frequent oil/filter changes, and regular valve clearance checks/adjustments. And some four-strokes (RMZ450 for example) have a manual timing chain tensioner that must be regularly checked/adjusted. Everything else is exactly like a two-stroke.