popping in a carb?

i am riding a 79 kz650d. i was out riding with a bud yesterday. all together i put on a little over 220 miles yesterday. the bike ran great all day. we stopped at his house for a soda an BS session. when i started back for home i had some popping in a carb. i thought maybe after it warmed up it would go away. well it didnt. i check my book and it said to check the timing. that checks out. it also said maybe bad gas but it seems to only be coming from one carb so i dont think that is right.
what do i check next?

thanks guys

Does the popping come on right off idle only or at throttle settings? If it is right off of idle and the bike ran great all day I would say you have some dirt in the idle circuit. Usually popping back through the carbs is s sign of a lean mixture.

it pops at idle and half throttle. i did find that the number one and two carb boots loose. i tighten them up and it seemed to help alot. it still does pop. it will pop and run fine for a couple miles and then pop and be fine for 15 miles? its nothing i can get to do when i do this or that? maybe i have a boot starting to crack?

what is the wd40 thing? spray the boot and if the stops its the boots? but it has to be popping all the time right?

when you find an answer let me know I have not been able to figure it out either went for a 500km ride yester day and towards the end it was popin ever once awile as well bet runnin very well any ways.:S

update!

i went back and started checking everything. first thing was the timing. this time i checked with a dewll meter and not the feeler gauge method.

first off if you dont have a dewll meter get one.

even though the feeler gauge method said i was on. i was off by enough. set my time by the dewl meter. got it at 90 degrees and she came to life. now she is acting like a naughty little girl!:evil: :evil:

How does one check timing with a feeler gauge? Just curious...