Sunbeam Alpine cough
Posted: Tue Oct 15, 2019 10:52 am
A brain teaser for you!
My car, which I have owned for 40 years, is a 1965 Sunbeam Alpine Series IV, 1592cc engine with a 28/36 Weber carburettor.
About 4 years ago it developed a backfiring cough when accelerating, particularly going uphill. The cough happens when pushing the revs up around 4000rpm in second or third gear and takes the form of a backfire through the carb (flames out the top with air filter removed) which causes a cough and stutter. The problem clears if I slow down and crawl up the hill!
So far I have:
• Replaced the fuel line from tanks to carb.
• Fitted a quality electric fuel pump to replace the mechanical one – including an in-line filter
• Overhauled my current Weber 28/36 at least 3 times and tried a replacement newly reconditioned unit in its place. Both carbs properly set up with recommended jet sizes.
• Fitted new coil, new distributor with electronic ignition, new HT leads, rotor arm and spark plugs.
• Fully reconditioned the cylinder head with new valves, guides and springs. All valve clearances and timing set correctly.
• Replaced the servo (after finding fluid in the drum and some evidence of it getting into the induction system – I thought that was the one!)
• Visited two diagnostic tuners, both of whom have recreated the problem on the rolling road but neither of whom have diagnosed the problem.
The problem still persists so any ideas welcome!
My car, which I have owned for 40 years, is a 1965 Sunbeam Alpine Series IV, 1592cc engine with a 28/36 Weber carburettor.
About 4 years ago it developed a backfiring cough when accelerating, particularly going uphill. The cough happens when pushing the revs up around 4000rpm in second or third gear and takes the form of a backfire through the carb (flames out the top with air filter removed) which causes a cough and stutter. The problem clears if I slow down and crawl up the hill!
So far I have:
• Replaced the fuel line from tanks to carb.
• Fitted a quality electric fuel pump to replace the mechanical one – including an in-line filter
• Overhauled my current Weber 28/36 at least 3 times and tried a replacement newly reconditioned unit in its place. Both carbs properly set up with recommended jet sizes.
• Fitted new coil, new distributor with electronic ignition, new HT leads, rotor arm and spark plugs.
• Fully reconditioned the cylinder head with new valves, guides and springs. All valve clearances and timing set correctly.
• Replaced the servo (after finding fluid in the drum and some evidence of it getting into the induction system – I thought that was the one!)
• Visited two diagnostic tuners, both of whom have recreated the problem on the rolling road but neither of whom have diagnosed the problem.
The problem still persists so any ideas welcome!