Hi just looking for a bit of help. I have a misfire on the offside pot on this bike, the nearside seems perfect. New plugs fitted and timing set. It starts first kick but the off side pot seems to be out of sync. It has had a conden sectomy could this be anything to do with the problem. A mate told me it could be down to fuel feed and mentioned a Bias gasket on the carb, no idea what a bias gasket is. Any info would be great help. Many thanks.
A bias gasket is thicker one side to tilt the carb towards the weak cylinder. If that was the cause I would expect to see some signs of weakness or richness on the plugs.
As the mag had had a condesectomy I presume there was a mag problem. A new condenser will not fix other mag problems.
I would suggest as a start that you swap the whole HT for each side from one side of the mag to the other and one cylinder to the other - the pickup and brush, the HT lead and the plug cap. If after that the problem moves cylinders you will know that there is a fault in that HT.
If not then check the cam ring for carbon deposits - some pattern brushes are too soft and leave deposits - check the points gaps on each cylinder, they should be within 3 thou fully open according to Lucas - check the earthing brush - check for play in the mag bearing, if you grasp the points bolt with pliers can you move it up and down.
You could try reducing the plug gap temporarily to 10 thou if it runs better then it could be a weak spark. Make sure that you have copper cored leads and a non resistive cap. Have you swapped over the plugs. If the mag is old and of course they all are it could be loss of magnetism giving a weak spark.
Thank you Julian & Idie for all your info, will go through it all and let you know how i get on. Stay safe.
Hi Julian & Idie well we have checked out all your suggestions and everything seems ok but to no avail. someone told us to check valve settings and carry out a compression test. Being novices we decided to take a look and found the tappets (if thats the right word) were screwed down real tight with no Movement, adjusted these still nothing. can you explain to me in laymans terms lol how to carry out a compresion test and what the readings should be. Looks like it may be a strip down job. Many thanks for your help. Bud.
Hi Bud,
Before doing any striping down. Did it have this misfire before the condenser was replaced? If not then it must be to do with the mag, HT leads, plug caps etc. as has been mentioned. Usually if there is no valve clearance it is not really until the engine warms up that the expansion of the valve gear will hold a valve open unless the adjusters were screwed down so much as to stop a valve from closing at all. If the engine has been run with a valve kept partially open the valve could have a burnt seat that may cause a misfire. How easy is it to kick over? Can you feel the resistance of the compression as you turn the engine.
What colour are the plugs after it been running?
For a compression test you will need a gauge that screws in to the plug hole. For an A65 with 7.5:1 pistons the reading would be 65-70 on the first kick with an average of 120-125 after that. I would think that an A7 would be about the same.
A lot of questions but the answers may help with the diagnosis.
Dave.
Just another thought. Does it have separate exhausts? Is there a difference in the deposits in the end of the silencer?
Hiya guys sorry for the late reply and thanks for all the info. The state of play at the moment is the head is off and the valves are out, there was quite a a bit of burning if thats the word and there was a considerable amount of play in the guides, so can i ask your opinion as to what guides are the best to fit. Do i fit Bronze or cast iron. Thanks for all your help and fingers crossed this does the trick. Stay safe Bud.
You should fit bronze valve guides on the Shooting Star. They were fitted as standard. It is to do with the expansion rates of the head and guides being similar.
Thanks for all your help on here guys. New valve guides fitted, a few bits and pieces and a bit of tlc now running sweet.