Won’t cold start/choke.
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holty
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the original backfire could have blown a gasket on the inlet manifold or the base of the cylinder, ive just had this happen to me, a leak down test would be a good plan before you start messing about with jets as trying to re jet around an air leak.
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holty
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a leak test is to check that the crankcase, cylinder, head and manifolds dont have any air leaks. an air leak will give running problems which if not fixed will lead to overheating and detonation, melting the piston or heat siezing. i use a blood pressure guage and hand pump and an adapter to fit into the carb rubber, and a rubber hose to go over the exhaust stub which is blanked off, when thats all fitted i simply pump up the pressure into the inlet manifold and look at the gauge it should hold pressure, if its leaking use warm soapy water to find out where from and fix the leak, then re test, i always leak test all engines i build, just to be safe.
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Jasio
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- Main scooter: Lambretta TV175
- Location: Devon
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That’s very helpful thank you. I have a couple of blood pressure cuffs and pumps so I will look to adapting as necessary. Great stuff folks. I’m not the sharpest at getting in here. But really appreciate the way people are helping out. 
holty wrote: ↑Wed Sep 16, 2020 4:24 pm a leak test is to check that the crankcase, cylinder, head and manifolds dont have any air leaks. an air leak will give running problems which if not fixed will lead to overheating and detonation, melting the piston or heat siezing. i use a blood pressure guage and hand pump and an adapter to fit into the carb rubber, and a rubber hose to go over the exhaust stub which is blanked off, when thats all fitted i simply pump up the pressure into the inlet manifold and look at the gauge it should hold pressure, if its leaking use warm soapy water to find out where from and fix the leak, then re test, i always leak test all engines i build, just to be safe.