backfiring through carb

[nezza]

hi all, having a problem with carb ,best way to explain is it starts up ok on choke but when engine is warm and push choke in and press accelerator it backfires thruogh carb, I have set timing up changed dizzy changed three carbs coil and same problem ,I have also fitted a new fuel pump this week ,on tickover it seems to be slightly up and down on the revs I have adjusted mixture but still the same problem and begining to think could it be a valve,your thoughts greatly appreciated.

[silloyd]

I had some backfiring problems recently (accompanied by general rough running) that I eventually discovered was caused by a faulty condenser. don't know if that would be your problem but it's an easy thing to replace to see if it helps.

[nezza]

thank you, will try that tomorrow ,

[kittyfell]

Have you checked the valve gaps? Or done a compression test?

[nezza]

will check valve gaps 2moz ,been 4 days on it now and dont seem to get any where ,but wont give up lol,must be geting to old

[nezza]

finally fixed it today ,turned out to be needle not centred in carb and was the same on other 2 carbs lol,if this is any help to anyone,nezza.

[bmcecosse]

Seems very unlikely ............ The needle is NOT centered in anything - it clamps firmly into the piston! Although in early SUs the jet certainly has to be centered on the needle, maybe that's what you mean? Boils down to checking if the piston can rise and fall freely - a check I often advise as a 'first step' in case of problems.

[nezza]

Hi,yes what I done was took piston out, undone lock nut at the jet a couple of turns pushed piston into jet and tightend lock nut which must of centerd needle into jet and bingo sorted,now runs great.

[bmcecosse]

Ahh - right, so you centered the JET!