I have a 71 Suzuki 125 ts 2 stroke have spark fuel compression bored new piston / rings still will not start

65 lb compression doesn't sound very much but could be fairly normal on a fairly highly tuned 2-stroke at kickstart speed, especially if the piston, rings and bore are dry.

Exhaust tuning causes a 2-stroke engine to grow in capacity when it is "on the pipe" resulting in a sudden increase in compression ratio and pressure and so if this is not to cause devastating detonation the designer must make allowances and probably utilise electronic automatice timing retard. Starting with a lower compression ratio is another method.
Having said that I would have expected at least 100 psi pressure and probably a little more...

Assuming you checked the new cylinder thoroughly before fitting and ensured all the ports including the transfer ports are open and correctly line up with any ports or recesses in the crankcase and ditto with the base gasket...
Assuming you checked the piston size matched the new cylinder and the piston rings were correctly gapped prior to fitting...

These things should not be taken for granted and should be checked to ensure they are correct. Assuming you did these things and assembled everything correctly (especially getting the piston the right way around) with a smear of clean oil a good induction should be assured and the compression should be almost as good as it is ever going to be.

I suggest you ensure there is a good spark and fuel is reaching the cylinder. If it isn't I suggest you revisit the new parts you fitted and the way you fitted them before investigating anything else.
Good luck!

Did you check the timing? If the timing is off there will be a reduction in performance and power will be greatly reduced. If the engine is "pinging" or "knocking" under heavy acceleration, your timing is advanced, and pre ignition is occurring (that's when the spark has ignited the fuel in the combustion chamber prematurely), resulting in a knocking sound. When the piston is compressing the air/fuel mixture within the combustion chamber, the spark plug produces a spark from current it receives from contacts closing in the distributor cap. (Where all the spark plug wires are plugged into) if that spark come BEFORE the piston finishes it up stroke or compression stroke, the piston is then being slowed down from the kinetic energy produced by the exploding fuel. Thats where we loose our power. Idealy, the spark should come AFTER the piston has rotated over the top of its stroke, It has reached its limit in compression and is on its way back down then the spark should ignite the compressed fuel, thus giving the piston an additional "shove" back down to start its "Power" stroke, once its reached the bottom of the power stroke (stroke #2 of 4) it is then carried back up for the "exhaust" stroke pushing the burnt fuel out of the combustion camber and into the exhaust manifold, one it has reached the top of that stroke it begins its journey back down to start stroke number 4, the Intake stroke. Drawing in air/fuel mixture to again be pushed back upward to compress the air/fuel, and repeat the process over and over again. Now that I have thoroughly bored you to tears, Yeah, check the engine timing, if its not the timing it may be a vacuum leak.

how much smoke because 2 stroke engines do blow quite a lot of smoke it is normal as you mix oil with fuel to lube the cylinder walls and the piston

I would be checking compression it may not be visible score on cylinder but it does not take much to loose compression on small bore motor with one piston ring and 11 years old

sounds like you have a bad set of rings on one cylinder,or a bad valve set.
the stronger compression cylinder will burn richer due to the fact that the lower compression cylinder isnt pulling a hard enough vacumme to draw in all the fuel that is dumped into the intake.when the good cylinder makes it intake stroke it pulls in the excess fuel and a fresh amount from the carb.

im leaning more towards the valve train on the bad cylinder due to the white smoke comming from the carb,if the intake valve isnt seating properly,you will have compression escaping,back feeding through the intake.but yoy should hear a popping along with the smoke,everytime the engine fires that cylinder.
hope this info helps you.

4 stroke
#1 intake stroke
exhaust valve closed,intake valve open.as the piston is on its way to the bottom of the bore,it creates a vacumme.drawing in the air/fuel mixture from the carb.when the piston hits the bottom of its downward travel,the intake valve closes,then the next stroke comes into play.

#2 compression stroke
after drawing in the air fuel mixture,the intake and exhaust valve are both closed.the rotating momentium pushes the piston back up the cylinder,compressing the air/fuel into the cylinder.

#3 power stroke
(depending on the timing)when the cylinder reaches top dead center (tdc)in the bore.the spark plug ignites the fuel,which causes the air/fuel mix explode.that explosion forces the piston back down into the bore.when the piston travels down,this stroke is completed.

#4 exhaust stroke
after the power stroke,the piston then travels back up the bore,while opening the exhaust valve.the moving pistion then pushes the exhausted air through the exhaust chamber and out the muffler.

then the cycle starts over again.
so if you have a valve thats not seating properly,on compression stroke you will have loss of compression,on the power stroke,loss of power....forcing that ignited fuel back through the valve that isnt seated corectly(if intake) you will get white smoke and a poping sound from the carb.on the exhaust stroke it will sent exhausted air back through the intake aswell.

once again i hope this helps,id dig into the valve train on that cylinder.

nick

get a compression gauge and test the engine compression, since it is old it most likely needs to be bored out and have new piston and rings installed

I suggest you bring the pistons to TDC, one at time on the comprssion stroke and do a "cylinder leakage test". Put compressed air into the spark plug hose and try to detect where the air is going. If you have the piston exactly at TDC, it will stay there when you put conpressed air in the hole, if it's off a little it will push the piston down. If you have the valve cover off you can watch the valves to determine if you have the pistons on the compression stroke. You should be able to buy a fitting from an auto parts store that will thread into the spark plug hole. If not take an old spark plug and bust the guts out of it and weld a pipe fitting to it to adapt your air compressor hose.

do a leak down test,and compression test,if your cyclinder is damaged you will have to bore it and replace your piston,and if you have an exhaust valve you may need to adjust or replace. check exhaust system could be clogged

• If a hole in the piston then install new piston and rings. Next, clean the carbon off the head and install a new head gasket.
• If cylinder wall is scared the piston has seized up. Pull the cylinder off and take it to the dealer. Have them bore the cylinder and return it along with a new oversize piston and rings.
• While at the parts counter, get a new stock spark plug and a supply of Yamalube Two Stroke Motor Oil. You need to add 4 ounces per gallon when filling up. This will be a 32/1 gas to oil ratio. NEVER ride the bike without at least the needed 32/1 mix.

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