back fireing

[bleddyn]

I'm having problems with my moggy,had previously had problems with electrics etc, but now have backfire when trying to start,so have done carb repair kit,also have done timing previously with strawb gun,but the backfire so bad , cant get moggy to keep going,and to warm up for me to recheck the timing with gun, so any suggestions''''' thanks

[bmcecosse]

Back fire - as in explosion in the exhaust that scares children ? Or - do you mean spitting back through the carb ? Need to know what has been done - most likely explanation is spark plug HT leads on wrong plugs! Check it's 1342 anti-clock around the dizzy cap.

[bleddyn]

Back fire - as in explosion in the exhaust that scares children ? Or - do you mean spitting back through the carb ? Need to know what has been done - most likely explanation is spark plug HT leads on wrong plugs! Check it's 1342 anti-clock around the dizzy cap.

BACKFIRE as explosion, have done all leads everything that way is good

[bleddyn]

backfire as an explosion

[mike.perry]

Are you sure that No 1 lead is on No 1 cylinder and not 180 out? Double check. Swap the leads over 1 to 4 and 3 to 2 and try again.

[bmcecosse]

If it starts and runs -and creates a backfire in the exhaust - then likely it's a stuck open exhaust valve, or a badly burned exhaust valve - or maybe - just maybe - it's an exhaust valve gap that's closed up. Petrol gets pumped into the exhaust - and is ignited there by the hot gases from the other cylinders. Off with the rocker cover - and observe the valves opening and closing as you crank the handle -and set the gaps to 12 thou inlet and 15 thou exhaust. To check for burned valve , you would need a compression test, although you may feel 3 good pulls on the handle, and one very 'soft' pull.