Ii have a 1970 honda ct 90 i bored half mil new piston and rings hand lapped valves new timing chain and tentioner and it smokes bad it has 150 lb compression on 5th kick what causes this

Appears you are burning oil intermittently. Ring job in order.

There are a number of possible reasons to get smoke including:
Cylinder bore scored, causing rings to not seat.
Damaged rings during piston replacement
Valve guides leaking
Mixture wrong (is smoke blue, white or black?)

Possibly bad rings or a leaking gasket

New valves, valve guides, valve guide seals; all fine but probably not needed. When the piston was changed, did you run a cylinder hone in the bore to check for distorted cylinder walls? Was the old piston seized up at any time? Were there scratches or grooves cut into the cylinder wall from being seized? Did the new piston get new rings? Chances are you will need to have the cylinder bored then install a new 1st oversize piston and rings. Please rate my answer.

Blue smoke is usually a cracked piston ring or worn out oil ring.
The only time the valves should be suspect is if the valves were recently lapped or replaced.
It's possible in those cases that the valve seals might leak oil into the cylinder.
Most often though, you will be looking at the piston rings, and the cylinder itself might need to be honed or bored.
If the cylinders need to be bored because of gouging due to scraping of the cracked or shattered rings, then you will need an oversize piston and rings to fit the new bore.

Getting the timing chain back on these engines can be tricky and requires more than just a diagram to get right. Here is how the timing chain should be reinstalled. Keep in mind that this engine can cause damage to the valves if the timing chain has any problems while the engine is running so it may not be a bad idea to setup the timing system as follows and do a compression test to make sure that everything is in order there.
Install the crankshaft sprocket with timing mark at the 5 o'clock position. Lower the timing chain through the opening in the top of the cylinder head. Carefully ensure that the chain goes around both sides of the cylinder block bosses (See 1 & 2 in picture): http://gsi.xw.gm.com/image_en_us/gif/000/000/412/412535.gif

Install the intake camshaft sprocket with the INT diamond at the 2 o'clock position. Hand tighten a NEW intake camshaft sprocket bolt. Route the timing chain around the crankshaft sprocket with the matching colored link aligning with the timing mark. Route the timing chain around the intake camshaft sprocket with the uniquely colored link (1) aligning with the INT diamond: http://gsi.xw.gm.com/image_en_us/gif/000/000/466/466558.gif

Install the timing chain tensioner guide through the opening in the top of the cylinder head. Tighten the timing chain tensioner guide bolt to 10 N·m (89 lb in): http://gsi.xw.gm.com/image_en_us/gif/000/000/412/412160.gif

Install the exhaust camshaft sprocket with the timing chain matching colored link (3) at EXH triangle aligned at the 10 o'clock position: http://gsi.xw.gm.com/image_en_us/gif/000/000/466/466570.gif

Ensure the timing marks and the colored links (1,2,3) are correctly aligned: http://gsi.xw.gm.com/image_en_us/gif/000/002/003/2003412.gif

Use a 24 mm wrench to rotate the camshaft slightly, until exhaust sprocket aligns with the camshaft. Hand tighten the NEW exhaust camshaft sprocket bolt: http://gsi.xw.gm.com/image_en_us/gif/000/000/412/412536.gif

Install the fixed timing chain guide. Tighten the fixed timing chain bolts to 10 N·m (89 lb in): http://gsi.xw.gm.com/image_en_us/gif/000/000/412/412165.gif

Apply sealant, GM P/N 12378521 (Canadian P/N 88901148) compound to thread and install the timing chain guide bolt access hole plug. Tighten the chain guide plug to 90 N·m (66 lb ft): http://gsi.xw.gm.com/image_en_us/gif/000/000/412/412164.gif

Install the timing chain upper guide. Tighten the timing chain upper guide bolts to 10 N·m (89 lb in): http://gsi.xw.gm.com/image_en_us/gif/000/000/412/412167.gif

Inspect the timing chain tensioner. If the timing chain tensioner, O-ring seal, or washer is damaged, replace the timing chain tensioner. Measure the timing chain tensioner assembly from end to end. A new tensioner should be supplied in the fully compressed non-active state. A tensioner in the compressed state will measure 72 mm (2.83 in) (a) from end to end. A tensioner in the active state will measure 85 mm (3.35 in) (a) from end to end.

****If the timing chain tensioner is not in the compressed state, perform the following steps. Remove the piston assembly from the body of the timing chain tensioner by pulling it out. Set the J 45027-2 (2) into a vise. Install the notch end of the piston assembly into the J 45027-2 (2). Using the J 45027-1 (1), turn the ratchet cylinder into the piston: http://gsi.xw.gm.com/image_en_us/gif/000/000/797/797246.gif

Inspect the bore of the tensioner body for dirt, debris, and damage. If any damage appears, replace the tensioner. Clean dirt or debris out with a lint free cloth. Install the compressed piston assembly back into the timing chain tensioner body until it stops at the bottom of the bore. Do not compress the piston assembly against the bottom of the bore. If the piston assembly is compressed against the bottom of the bore, it will activate the tensioner, which will then need to be reset again. At this point the tensioner should measure approximately 72 mm (2.83 in) (a) from end to end. If the tensioner does not read 72 mm (2.83 in) (a) from end to end repeat the steps required to return it to it's compressed state above.

Install the timing chain tensioner. Tighten the timing chain tensioner to 75 N·m (55 lb ft). Use a suitable tool with a rubber tip on the end. Feed the tool down through the camshaft drive chant to rest on the timing chain. Then give a sharp jolt diagonally downwards to release the tensioner: http://gsi.xw.gm.com/image_en_us/gif/000/000/412/412158.gif

Use a 24 mm wrench to hold the camshaft. Tighten the NEW camshaft bolts to 85 N·m (63 lb ft) plus 30 degrees: http://gsi.xw.gm.com/image_en_us/gif/000/000/630/630311.gif

Sounds like time for a top end job. New valve guides, ( lap the valves ), new piston and rings and possibly a new bore. Some bikes have nickle coated sleeves and cannot be bored, You can get a new nickle sleeve to replace the old one. Your dealer will be the best person to say if you need a new sleeve or not. Parts are around $275 with a new sleeve.

Your best buddy didn't put a shot of oil in the gas tank did he? Drain the tank and put the gas in your lawn mower. Sorry to be the one with the bad news. At least now ya know what ya gotta do.

Please rate this answer. Thanks gunman_54321 < cool name

id say its time for a new set of piston rings sounds like youv got a busted oil ring