hi, been out 3 times on this bike , first and second time after approx 20 mins the bike cut out and took a lot to re start , third time out it just wouldnt re start, checked old plug for spark and also tried a new plug both were sparking , took bowl off carb nice and clean, tried wire brushing old plug etc, now after searching could it be crank seals ?is there a way of testing , i seam to think there is less compression but cannot make my mind up, how hard a job is it to change these ,is there any pics or diagrams i could see or follow , by the way i have orerded new condenser and points, any help barry( i also checked fuel supply from tank )

Edited March 9, 201412 yr by codmaster127

To save a lot of unnecessary work, before you start pulling it apart you need to work out if it is a fuel or a spark issue.

To help with diagnosis, crank seals will not cause a bike to cut out. It will make it run lean when the throttle is in the closed and almost-closed position.

Even if the float bowl is clean, and fuel flows from the tank, that does not mean there is not a fuel problem. You should inspect the plug immediately after the failed start attempts to see if it is wet or dry.

Sudden cut-outs sounds a lot more like ignition problems. If it starts and runs when cold but cuts out when hot, it is most likely the condenser. If you haven't serviced the points, that can also make the spark less energetic. Also just because you can see a spark when you kick it over with the plug out, does not mean there is a spark when the plug is back in the motor, because the increased pressure in the combustion chamber means that a higher voltage is required for the spark to jump the gap. The colour of the spark can say a lot about the health of the ignition. Pale blue spark is the most energetic and yellow/orange/red is least energetic

as above wait until tried the new points and condensor

thanks for your advice anything is appreciated, i have ordered points and condenser plus a few other bits and bobs (in motion), the bike will not start at all now , first couple of outings it started first or second kick until i had ridden it for 20 mins or so, , iam i right in believeing if you remove the air box and put your hand over the back of the carb and slowly turn the engine over you should feel it sucking if not it could be crank seals , i have a friend who has offered to check carb out etc if the points condenser dont cure it,i would welcome any other opinions on the matter as i havnt had bikes for a long time (20 odd yr)

Had the same happen to me twice. The first time the fuel filter was partially blocked, put a new one in sorted. Second time different bike, the fuel tank breather on the cap was blocked by nipping of the pipe between tank and frame ! It was routed wrongly !

condensers breaking down due to overheating is a problem on these bikes most have had them moved if yours has not been done it is a good time to do it

if you are replacing points to move it up to near the coil to keep cool

i did check the fuel breather pipe when it cut out and was clear, i also tried it when i got home took cap off etc,still wont start, and yer as far as iam aware the condenser has been moved to under the tank,

sorry condenser hasnt alredy been moved, condenser and points arrived today not sure when i will be fitting them,

Condenser. All the other things you mention will make it run bad but a hot failing condenser will give an intermittent misfire, and gradual points failure.

By the time you push the dead bike up to the car park its running again? When you do move the condenser make sure its terminals clear the metal petrol tank.

discovered poorly piston and broken top ring , up to now no damage to barrel , couldnt get barrel off because i couldnt find the correct size allen key , ordered now,