Motorcycle Repair: gs425 sorry dude., vacuum leaks, intake runners

Question
hi, sorry to bug you again. i'm the guy with the dodgy gs425 overheating rh cylinder from a couple of weeks ago. how you doin? well, been messin with the bike every day going back to the begining and repeating everything hoping to find the problem. i've stripped the head and carbs so many times my fingers are numb. my missus is hating it. i ended boiling bits of carb in a pan the other day when i thought i found a blockage in the most smallest of holes, she wasn't impressed.
i've now come to the conclusion that theres just not enough fuel going through. the rh side is still overheating but the left is starving of fuel. i know this because i manually fed some petrol just into the left and the it revved albiet for a second. i now think i remember when i put the bike away the rh side was starting to overheat so could of just needed a good balancing session. but, now i've played with it and removed the airbox and replaced it with pods there's not a constant velocity?? this would kind of explain why blocking up the air intakes would make it rev higher. bigger main jets?? what do you think?? any imput at all would be good. asked in a couple of bike dealerships but they don't touch anything pre'84. i think my wife is going to set fire to it soon. cheers..

Answer
It will be almost impossible to properly synch the carbs now that they have individual filters. Get ready for more frustration. :-)

Yes, you will need to go to bigger jets now that you have increased the airflow going into the carbs. But before you attempt that, I have a suggestions you might want to consider. You should check for vacuum leaks around the intake runners leading from the carbs to the cylinder head. With the motor running, spray small shots of WD-40 (using the small red nozzle tube) at different spots around the runners, waiting a few seconds between squirts. WD-40 has kerosene in its formulation, so it will emit cloudy white smoke when burned. So if you squirt one area and suddenly see white smoke coming out the exhaust - bingo, you've found a vacuum leak.

One other thing to check is fuel flow to the carbs from the gas tank. Try bypassing the tank and fuel tap altogether by using a gravity feed system (a small container held above the height of the carbs) and see if the problem goes away. Use new fuel hose for this experiment, as it is possible the old ones have swelled almost shut from age and are restricting fuel flow.