recently ive fitted a forge d/valve to my classic and now im having backfire'n as i acelarate in 3rd and ez of in the same gear (sometimes in 2nd)
IS THIS DOING ENY DAMAGE
thanks......

 

It shouldn't backfire while accelarating. It probably will do when you change gear. It sounds like the spring is too weak, and its causing overfuel. This ignites when it hits the hot exhaust.

Is it new, and what colour spring does it have? It should be blue. Also double check there are no air leaks whatsoever.

MB

 

cheers butt,
the dump valve was new from revolutions and i think its the blue
plus ive got a blitz nur spec r system from down pipe back
but should it causes any damage

 

Exhaust will be no problem.

Still check for any leaks around the D/V. Sounds like its running way too rich to me.

MB

 

cheers again,
my mistake it only does it as im easing of in 3rd thanks...

 

That would explain it, and its reasonably normal behaviour with an atmos DV.

There are schools of thought which will tell you that long term this will cause problems. Cant remember what exactly, but maybe bore wash etc. Atmos DV's basically confuse the MAF quite a bit. There are worse things to fit though, and many people use them.

Best ask Bob Rawle, as he's got some genuine reasons to be against them.

Enjoy the flames / pops / bangs in the meantime!

MB

 

You also might want to experiment with a spacer or too (free from Forge) which will effectively stiffen the spring by shortening its travel. Good to do if you are running a bit more boost, or you get idle problems etc...

MB