Number 4 cylinder smoking

[Trkdrvr1376]

My 1980 750c barn find is blowing smoke from cylinder 4. Rebuilt carbs and it starts up with just a twist of throttle no choke.
After warmup it idles .
Rev it up and it smokes white.
It’s not registered but took it around the neighborhood and pulls great no backfire no hesitation. Compression on that cylinder is 138.
Pulled the plug and it’s black but not wet.
Smells like gas very noticeable.
I’ve adjusted pilot screw to lean it out but no
Change in smoke. Before I pull carbs am I missing something?
Any ideas would be appreciated
Thanks

 

[mrtwowheel]

Did you rebuild them with aftermarket jets and needles?

 

[Trkdrvr1376]

I used the original jets and needles, cleaned and seemed in good shape.

 

[brettp]

How long does the white smoke last? Usually white smoke is a water or coolant (but these bikes don't have coolanr) burning off.
Maybe water or condensation sitting in exhaust 4?

 

[Trkdrvr1376]

After playing around with the bike today I am embarrassed to say I screwed up when I cleaned the tank. I rushed and did not de rust it like I thought I did. So I will tackle the tank this week, next I will remove the carbs and clean them ,replace the filter and see what I have. Hopefully anyone trying to bring one of these classic old bikes back to life will learn from my mistake…. Take your time and check and recheck your work it will be worth it in the long run.

 

[Trkdrvr1376]

How long does the white smoke last? Usually white smoke is a water or coolant (but these bikes don't have coolanr) burning off.
Maybe water or condensation sitting in exhaust 4?

I removed the pilot screw and had it about 2.25 turns out so I reset it to about 1.25 turns and the smoke was less noticeably. So I was going to remove the pucks and check that’s when I noticed the rust colored gas.
So I am going to remove clean the tank and pull carbs , clean and replace the filter.
I rushed cleaning the tank. I am new at working on bikes but I am enjoying it and learning along the way

 

[brettp]

We were all there at one point. Some of the things I'll never forget are because I made mistakes!