Exhaust popping

[Devonboy]

Hi guys been having problems with my 2ltr air cooled engine. It was blowing petrol out the exhaust so I had a guy work on it. He did the following new plugs,dis cap,rotar,fuel pump,regulator took carbs off replaced needle valves and gasgets. New filters and adjusted timing. This cured the fuel prob and van went sweet however it's now began back firing when idling and driving, it also drives bad lack off power very lumpy. I've checked the obvious, pipes , leads but can't seem to get to the bottom of prob. Any thoughts guys would be much appreciated been goin on for to long and driving me mad, many thanks Ian

[BOXY]

Check the vacuum pipes, any leaks will weaken the mixture and cause problems with idle. Start at the left hand corner of the engine bay and check the rubber tee piece on the lower left-hand side of the carb isn't split or come off. Check the brake servo pipe that joins this tee isn't leaking. Next un-clip the air-box (four clip on the lid & two more holding it to the engine). Lift the box out and check the vac pipes that run across the engine & bulkhead. There are short flexis joining the metal pipes and these never get looked at. Finally in the right-hand corner of the engine bay there is a rubber elbow on the right-hand carb to check for splits & leaks. If the carbs have been off maybe one of the pipes got split or not re-fitted properly?

[Devonboy]

Still no joy Boxy

[kevtherev]

Still no joy Boxy

it's getting air to weaken the mixture from somewhere, or the mixture isn't right in the first place. Is the distributor diaphragm OK?
The leads are on right?
the timing is right?

[BOXY]

Have you got a strobe light you can use to check that the mechanic has set the timing correctly? If it's been set with the vac system not working properly it could be miles out. Did he re-gap the valves when he did the work? If he's set the clearance on an exhaust valve too tight that could be causing the lack of power & back-firing? What filters did he change? Check the fuel filter under the van by the fuel tank it should be the only one on the fuel line. Check to see if someone has fitted an extra one somewhere in the engine bay.

[horizontal kipper]

Is the dizzy the original electronic one or has it been changed for a points and condensor one? if points the condensor could be at fault.

[Devonboy]

Thanks guys