Back firing through the carb

[collidg]

Hi i am having trouble getting the car to run smoothly, it is backing firing through the carburettor, i found a crack in the mainifold which has been welded, new gaskets fitted, checked the compression all ok, ( fitted with single stromberg) altering the timing on the dizzy does not seem to make much difference, any ideas greatly recived

[Orca2]

Originally Posted by collidg

Hi i am having trouble getting the car to run smoothly, it is backing firing through the carburettor, i found a crack in the mainifold which has been welded, new gaskets fitted, checked the compression all ok, ( fitted with single stromberg) altering the timing on the dizzy does not seem to make much difference, any ideas greatly recived

Had this once on a mini, turned out to be a crack between the valve seats in the head, exhaust was igniting the incoming fuel local machine shop bored out the valve seats and fitted a figure eight blank then recut the seats to suit valves it was pretty cheap and worked,could be a timing issue too.

[Clan]

Originally Posted by collidg

Hi i am having trouble getting the car to run smoothly, it is backing firing through the carburettor, i found a crack in the mainifold which has been welded, new gaskets fitted, checked the compression all ok, ( fitted with single stromberg) altering the timing on the dizzy does not seem to make much difference, any ideas greatly recived

I had this in the 1970's when the camshaft lobes had worn down which could happen on the B20 and B 30 engines ... Take the cover off and turn the starter after disconnecting the coil watch all the rockers and you may see one or two ( or all ! ) barely moving ...

[collidg]

Thanks for the advice, I have tracked it down to the camshaft. The lobe had worn away on number 4 cylinder exaust valve, and the exhaust fumes were escaping out of the inlet valve. Got a secondhand cam from Amazon cars, it had done 4,000 miles. The camfollwers and oil pump/dizzy drive was hard to get out, they had carboned up a bit, i damaged the drive in the process, however, Amazon cars had a spare one.