back firing 253

[thatotherguy]

Hi all,my sons prem keeps back firing mainly out of the left exhaust, we have changed carby,distributor,leads and it has fresh fuel and have just done a compression test and all are 150 even. we took this car off the road about 18 month ago and it was running fine but on gas,we have since removed the gas and put it back to petrol, it doesnt seem to have any vacuum leaks and the timing is good (have tried advancing and retarding it with no change) hope some one can help thanks

[Taily]

Mine started doing this recently after being laid up for a couple of years. turns out it was a stuck valve and it freed up after warming up properly. May sound silly, but have you double checked the firing order?

[wbute]

Have you timed it with a timing light or just turned the dizzy?

[thatotherguy]

we drove it on the first day and it was running rough but wasnt back firing,firing order is the first thing i checked and i used a timing light, i thought if the timing was out it would back fire through the carby but it only back fires through the left exhaust and it does it hot or cold

[wbute]

Pull the rocker cover and see if all the valves are opening properly. Although it sounds as though unburnt fuel is going into the exhaust. It may be a dodgy lead or plug?

[adam perth]

Stuck valve. Take covers off and wind over by hand until valve is supposed to open then hit top of valve spring with a hammer low to medium impact .

[Big Rob]

Yep, what Adam said.

A squirt of oil around the valve stem before you do it may help too.

It should settle down after that, it's just carbon buildup on the valve stem.

[thatotherguy]

Fixed, turned out to be a stuffed spark plug (brand new)
Thanks everyone for your help

[Robbo]

Annoying those sort's of issues, replaced to do the job properly, only to have one fail. If it happened to me, it would be the hardest one to access.

[adam perth]

Yeah that is annoying !