First post -hi from Cambridge

[fivelampboy]

Hi all,
Have recently taken ownership of an '87 plate TA 600 with 67k.. Have wanted one for ages and this old girl was the best and only option due to finances.
Ive given her a service; oil, coolant & plugs (they were fun ! ) but am finding there's something of a backfire when I change down gear. The bike ticks over happily but this prob is really getting me down and Im not really sure where to go from here.. I'm pretty confident working on bikes ( I did get the plugs changed ) but I'm stuck with this. ANY advice will be really appreciated from all of you knowledgable peeps and any cheap fixes will be even more appreciated.
many thanks

[Mabels Old Man]

Stumps will be along in a moment to say welcome to the forum so until he does welcome to the forum. There's a wealth of knowledge on here to be tapped into. There's also a load of technical numpties, time will show where I fit in. Oh and we don't take ourselves to seriously.

[Lutin]

Hi and welcome to the Asylum.

The back-firing may be due to an air leak on the inlets. Things to check are that the carb rubbers are seated correctly - they can be distorted by being over-tightened.

Worth a look see, if nothing else.

[StumpyFingers]

Hello and welcome to the forum.
Besides what has been mentioned above it could have an over tight valve which stays open too long, allowing unburned fuel into the exhaust which then ignites causing the backfire.

[fivelampboy]

Thanks ever so for the welcome and getting back so promptly -
I understood everyting up until the asylum bit, you lost me after that
Any way.. I've had the tank, panels, seat, fairing off and the only air intake "anything" i can see is the air filter and it's path to the carbs. I've replaced the hose rings on the rubbers that fit on the tops of the carbs and the rectangular box thing under the seat, air filter is clean and intact; otherwise I'm not really sure what you and stumpy mean
where are these air inlets and the valve you mention ? I think the labels have fallen off over the years so you'll need to be graphic
Thanks fellas, It's nice to belong