where do i start or who do i seen.still go heaps of power only happens under compression any ideas guys.
running twin webbers

try techtalk valves to tight??

What do you mean by "under compression" ??? Backfiring with most any carb setup normally means lean....

If the engine's been running OK previously and has only just now started playing up, I'd be thinking maybe a blocked jet - something that's pretty common with Weber IDF's actually. If the carbs or throttle linkage have been apart, well I'd suspect they haven't been setup and tuned properly after being put back together.

If you're planning on doing stuff yourself, as a good starting point take a read through http://www.aircooled.net/gnrlsite/resource/articles/jetting.htm and http://www.aircooled.net/gnrlsite/resource/articles/dualcarb.htm.

find someone who knows what there doing fora start before u stuff the engine

under compression im guessing u mean over running down hill??

if its popping and farting then u probably gotta zorst leak somewhere
most likely those bastard donut rings that seal heaterbox/Jpipes

Backfiring on run on can be caused by either a leak in the exhaust and/or a leak in the intake manifold.

If, when the engine is idling, you very carefully (keep fire in mind) spray the intake system from the carby to the heads with something like Start Ya Bastard and it revs up a bit, you've found the intake leak.

An exhaust leak can be found by putting a suitable hose to an ear and moving the other end around the exhaust system.

If you find either one of those leaks, you may have found your problem.

thanks guys for all the ideas it was a leak near heat exchange

http://au.youtube.com/watch?v=qcpRX9Jn068 

eh?

thanks to westside mufflers great job car going great no problems now

Rob, What were you doing up that early on a saturday morning??????

hey noddy need to catch up to get speedo thanks mate