Hello there and thanks in advance for your help!!

I have a 1980 XS400. It is only firing on one cylinder, the left one. I checked for a spark from the plugs. and in the problem cylinder there was no spark from the plug. To investigate i:

swapped High tension leads (the ones from the coils to the plugs) no change, the right cylinder still no spark.

then

swapped the coils. the spark then appeared at the right and not the left.

so i am assuming that the coil is broken and when i replace the broken coil i will fix the problem. am i correct?

is there another way i should have gone about checking this or can i be sure that the coil is at fault?

also i have had to upgrade the right exhaust pipe because the muffler was too damaged. i have added a universal one. however the left exhaust had a support bar between the two that is now open and obviously noisy. any tips on how block it or clamp it closed to ensure that all the exhaust gas goes out the back.

the guy who sold me the muffler said i should fit two universal mufflers to balance the back pressure. should this be a major consideration of mine?

thanks for you help,

Chris

You need to check that you are getting power to both of the coils. It might not be a faulty coil.

The exhaust system has a balence pipe which is now open. You should have changed the exhaust (muffler) for the same type and fitting. Failure to do so can leave the engine running roughly. It is not as simple as just blocking off the balence hole. Things are there for a reason.

You should check that you have power to both coils before changing anything. With a fully charged battery you should see 12v plus.

One old bikes it is a good idea to renew the high tension leads and spark plugs anyway.

You need to check that you are getting power to both of the coils. It might not be a faulty coil.

The exhaust system has a balence pipe which is now open. You should have changed the exhaust (muffler) for the same type and fitting. Failure to do so can leave the engine running roughly. It is not as simple as just blocking off the balence hole. Things are there for a reason.

You should check that you have power to both coils before changing anything. With a fully charged battery you should see 12v plus.

One old bikes it is a good idea to renew the high tension leads and spark plugs anyway.

My xs 400 was doing that, among other things, changed the plugs runs okay now (thanks to a bit of help from yoda,)

You need to check that you are getting power to both of the coils. It might not be a faulty coil.

The exhaust system has a balence pipe which is now open. You should have changed the exhaust (muffler) for the same type and fitting. Failure to do so can leave the engine running roughly. It is not as simple as just blocking off the balence hole. Things are there for a reason.

You should check that you have power to both coils before changing anything. With a fully charged battery you should see 12v plus.

One old bikes it is a good idea to renew the high tension leads and spark plugs anyway.

the balance pipe in the xs400 was to effectivley lengthen the pipe so they (yamaha) could fit a shorter silencer to get the look right and still comply with the regs.