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Jan 26, 2008 6:44 pm
Jan 26, 2008 6:44 pm
Subject: Re: 2L engine problem
As I said above, if the lobes are very flat the valves stay open longer. Especially with much valve overlap, this causes petrol to be pushed back through the inlet valves and then the air inlets of the carburetter; no matter if it is sidedraft or downdraft, although it would be worse in the latter case as the distance between valves and carburetters is shorter.
The solution is to buy camshafts from the club which have rounded lobes (see picture in my posting below). I could also recommend to reduce the overlap to about 24 degrees or so - more overlap is only useful at very high revving; at lower speeds it actually works counterproductive.
As I said above, if the lobes are very flat the valves stay open longer. Especially with much valve overlap, this causes petrol to be pushed back through the inlet valves and then the air inlets of the carburetter; no matter if it is sidedraft or downdraft, although it would be worse in the latter case as the distance between valves and carburetters is shorter.
The solution is to buy camshafts from the club which have rounded lobes (see picture in my posting below). I could also recommend to reduce the overlap to about 24 degrees or so - more overlap is only useful at very high revving; at lower speeds it actually works counterproductive.