Failing coil/s

Starts and idles okay......not brilliant. Soon as it gets hot it misfires and splutters but picks up intermittently. Plugs are the recommended grade but I could try a hotter plug as it is running a wee bit rich?

Going to hotter plugs is masking the problem, have you check compressions? It might be caused by a valve issue. Have you got more details about how this problem occurred, suddenly, after a drag etc.

What makes you think its the coils? or spark for that matter, is the voltage correct at coil input (battery voltage), how old are the spark plugs (what colour are they on the electrode) currently in the engine etc. Please give more details.

Did a compression test and all is okay. It's definitely an electrical issue because when I rebuilt the engine I did all the top end work that was needed. I've had the carbs off numerous times and fuel wise it's fine.

It's really strange because every now and again it seems to be firing on just three cylinders, usually 1 or 2 seem to stop. But only one goes at a time. Funny thing is if I pull the cap from the plug whilst it's running and hold it 1/2" above the plug it suddenly picks up and all 4 fire. It has nearly new BR8ES plugs and new caps, very strange problem?

Bad coils. Open wire inside the coil.
Steve

JoHNY wrote: Did a compression test and all is okay. It's definitely an electrical issue because when I rebuilt the engine I did all the top end work that was needed. I've had the carbs off numerous times and fuel wise it's fine.

It's really strange because every now and again it seems to be firing on just three cylinders, usually 1 or 2 seem to stop. But only one goes at a time. Funny thing is if I pull the cap from the plug whilst it's running and hold it 1/2" above the plug it suddenly picks up and all 4 fire. It has nearly new BR8ES plugs and new caps, very strange problem?

Would double-check valve clearances, which can be too tight regardless of good compression test results.

With the R spark plugs, hopefully the new caps are zero resistance and the plug wires are solid core (non-resistant), because otherwise there's too much resistance in the secondary loop resulting in weakened spark.

Old worn hard cracked spark plug wires can also cause the reported condition.

Rich running can also be caused by too high fuel levels. If not already done, would perform clear tube tests.

Good Fortune!

Update

Bought new coils, HT leads and hotter plugs. Issue sorted, running sweet as