Can a backfire be due to running lean also?

[encieno]

I've been messing with my 94 Katana forever now. It seems once I fix something, something else goes bad. Basically I found a bad chain to be the primary source of my engine running poorly... The chain was warped and was getting caught up on each sprocket, making the RPMs jump up and down. In the course of troubleshooting that, I was messing a lot with the carbs, and eventually dropped the main jet back down to 115, with the needle being on the second clip. Now that I got the chain fixed, the bike was running like a dream, after months of messing around with it, haha. I decided I would go ahead and raise the floats some more, and drop the 120 main jet back in. With the weather getting colder out<not sure if this is causing anything>, it's been backfiring like hell when the engine is cold. I'll have to run like 9-11k RPMs for a good 10-15 minutes just so it won't backfire when I let off the gas... Today I ripped the 120's out, stuck the 115's back in. Still backfiring. I took the needles out to check them to make sure they still looked alright, and noticed the clip was at the second position. OOPS, I had forgot about that. By this time, it was the third trip around the block, and the engine was slightly heating up. I had no backfires at all this time, and was trying to get it to backfire, low gears/low rpms to see if it could somehow flood it out.
This time, I'm unsure if raising the needle helped, or if it just took a while to get the gas burnt out of there, and maybe the 115 main helped.

And FINALL, the question!

Is it possible that the 120 was pushing too much gas in, and the needle being at the second clip, was making it run too lean to ignite all the gas? The gas was being trapped in the cylinder until the next fire, causing the backfire? Why would it run better once it heated up? I'm trying to figure it out but really don't know enough about how heat effects combustion.... I thought the colder the better, that's why I'm confused as to why the heated up engine makes the backfires go away. I'm currently letting my bike cool down<got fans blasting away on it!> so I can run around again quick before calling it the needle clip position. If this fixes it, I will probably toss the 120 mains back in to see if that does anything...
Thanks

[md86]

Well , if it's runnin lean , it'll run better once it warms up . Rich will run better cold , then crappy warm . A cold engine needs a richer mixture to run right , becasue the fuel won't vaporize/mix right until it gets warm enough .
In the meantime , you seen this yet ?

http://66.47.68.116/tech/carbtune,CV,high_rpm_engines.html

[encieno]

yeah, that's what i thought, and i've seen that page. that's why i'm completely confused by this, haha.
a quick update, earlier i put the 120's back in, dropped the clips one position again.. .so far, no backfires. i'll see tomorrow morning going to work if i start 'shooting' at people driving by, haha. it's always funny seeing people startled over it.

[md86]

Well , your plugs should tell you if you're rich or lean . and maybe look for a shop nearby with a dyno/EGA so you can know FOR SURE what it's doing . Usually about $20 or so a run . I was charged $20 for about 15 minutes of shop time , which included the guy running the bike in different ways to get a good idea what was going on , not just a peak horsepower run .

[encieno]

once again, i'm on the wrong path. the damn kickstand was falling down partially up and down i guess. today it fell completely off the switch plunger and killed the engine on the highway, hahaha. it was real fun pulling over. luckily i had tie wraps to tie it up. i'm going to cut the switch now =]

[md86]

: How often we overlook the most simple of things sometimes .