Carb cough, or after fire

[Williams1]

I was starting my VW saloon 1600 racer and whilst it was cranking, the carbs (dellorto 40's) began to splutter/'sneeze' as usual, but then...BOOM! I wasn't able to identify if this colossal noise had emanated from under the bonnet or from the exhaust.

Whilst the engine wasn't running, it was turning over at the time, so I don't know whether it is still possible for excess fuel to ignite in the exhaust manifold or not, or whether it is more likely to be a case of excess fuel (the engine was probably slightly flooded) igniting in the inlet manifold while the valve to the first cylinder was still open? Any ideas as to what it is will be greatly appreciated.


Whatever it was it cant of been great - I've checked for any superficial damage to the carbs, but a bent valve, scored piston or blowing inlet gasket is the last thing I need! The cars running standard valves so I'm not sure of the kind of tolerances they can withstand.

Thanks,

Oscar.

[Chris Y]

> igniting in the inlet manifold while the valve to the first cylinder was still open?

Probably. Particularly if you have a long duration cam with a bit of overlap.

Probably sounded more spectacular than damaging!

[Al Weyman]

Ha ha try starting a V8 race engine, you get fire in the hole and all sorts, you will be OK! Also I run my road car a Chevy Blazer on Autogas and when cold you can get a build up of gas in the inlet that can suddenly explode and that sounds BIG worst damage I have found is a bent plate in the air intake that pulls in hot air when cold.

[Tim Falce]

Be careful if you use foam filters as even when these carbs splutter back and don't go bang they soak the filter with petrol which eventually leads to fire when they do blow back flames, I've lost three sets of very expensive filters that way.

[Al Weyman]

Good point I lost a paper one once as well.