Thanks for your replys.
( Hej G�ran kul att man inte �r ensam svensk h�r !
) I might not have been clear enouch in my post so i'll try to clearify the problem.
The carb is not to lean as i get a slight blackish exhaust while reving the engine the carb is a brand new Speed Demon 750 and we have tried to alter the mixture back and forth with no result either.
The valvetrain has been alterd from the original pedestal design to adjustable roller rockers by the crane cam conversion kit.
Now here's a picture showing how loose the rockers are just after the valvecovers are removed with and engine at operating temperature. http://www.realvis.com/jonte/looserockers.jpg
Forest: Interesting that you write that the backfire can be caused by the exhaust valve not opening. When we had the valvecovers of and did the adjustment we could hear how it was popping back thru the carb while cranking it without the coil attached. then we started tightening the exhaust valves down a bit and the pops disappeared.
But since it was impossible to say wich of the rockers that rattled i can't say that adjusting the valve-lash while the engine runs is a very good solution but then again i cant adjust it with the engine of either since the spring action in the lifter just isn't there anymore or at least not on all of the lifters.
Anyway what i don't understand is if the rockers could be this loose or if there is something that just dont work as it should...and if the backfires now comes from a non-opening exhaust valve why does this occur...sudden drop in oilpressure or some other variation that takes place once the oil temperature rises higher.
I started reading on other forums too and saw that some people had problems with the cam-lobes beeing grinded down...This sounds unlikely since the cam,lifters,pushrods and other valvetrain parts are brand new and installed by the book. and broken in over a period of 20 minutes as specified.
Here's a picture of the whole machinery. http://www.soulcollector.se/nemesis/jpg/panterastuff/351cEngineInstalled01.jpg