Sputtering

Just aquired the bike back in Febuary, a 1981 XJ550 Maxim that has been converted into a bobber - (not by me) -
Had the thing out and about the last 2 weekends putting just over 300 miles (as long as odometer is working properly) on her, with the bike running like a top -
Only issue is that there is a small bit of sputtering going on when I am accelerating - its non-consistent though, if I jump on the throttle and accelerate quickly its not as evident but when I am gently accelerating it seems to be more evident - and sputtering does not happen at all during idle from what I can tell

Also I have noticed that there is discoloration ( a blue tint ) on the #2 exhaust pipe - close to the cylinder about 1-2inches away - the other pipes are discolored also but with a light goldish color (which seems normal?)
I pulled the plug out and checked it - which it was a fair bit darker than the others - but not corroded or damaged - I checked the gap and it seemed fine - my first thought is to replace the plugs since they have not been replaced yet and I am not sure of their age -

I will update this post after I get new plugs

 

What intake (pods?) or exhaust mods have been done to it?

How many miles on it?

Valves in spec?

 

Mine does this, and I assume it's due to the enormous crack in the exhaust...

I just bought a new one... so i guess we'll see.

Also. My bike is T-minus 3 weeks untill all the mods I do are cosmetic or fun, and not, REPAIR REPAIR REPAIR.

 

The bike has K&N air filter (pods) and I believe the baffle system of the exhaust has been removed and the exhaust system seems to have been shortened - the pipes end about 6 inches behind my footpegs

The carbs are jetted properly with these mods - I checked with the Motorcycle shop that opened close to my house when I was cleaning them