flames out the back

[G4O LP]

I took my car for an mot today after 2 years and I have changed the head to a bvh but apart from that its the same when I put my foot down it revs up then pops and a huge flame comes out the back.I have had the whole engine out as well

[PeteG40]

is it timed up correctly

[Wiggy]

This used to happen on my GT. I had changed the dizzy, and didn't time it up properly, and it used to pop some mahoosive flames! Found out when i checked the timing that it was very retarded. But I left it.....because i liked popping flames....lol

[Tommo]

Yeah, check your cam and ignition timing.

[scotsjohn]

And quickly too! You're looking to burn out your exhaust valve seats if your timing's that far retarded.

[DaBigGinger]

Sounds cool, leave it! 

[Wiggy]

Oh, it certainly is cool looking in the rearview mirror when you change gear and seeing the road light up....but as said, not so good for the engine perhaps....