Left side cylinders will not fire

The firing order should be 1 2 3 4 5 6
Your cylinder banks are odd and even numbered.
Looking under the hood, front bank of cylinders , from left to right, 2 4 6
The rear bank of cylinders, left to right, 1 3 5

Could be one of the carbs playing up. Maybe a blocked or restricted jet.

Re-check the R carburetor. Sounds like either a plugged Pilot jet or a Low Fuel level (High Float Level). Check the Sparkplug also -

have you tried fresh fuel. ie not the stuff that's been in the tank for a year. stale fuel usually causes problems with small 2 stoke engines, but it might be worth a try.

In the 4 cylinder the firing order is 1,3,4,2 and the cylinders are numbered 1,2,3,4 from the Passenger side to the drivers side.

In a V6 the firing order is 1,6,5,4,3,2 and the cylinders are numbered 1,3,5 in the front from the passenger side to the drivers side and 2,4,6 in the back from the passengers side to the drivers side.

a compression test would be a good step

Firing order 1-5-6-3-4-2-7-8
Distributor rotor turn's clockwise
cylinder's 1-2-5-7 left side of motor
cylinder's 2-4-6-8 right side of motor back side by fire wall.

Maintance

Keep up with your oil changes every three months or 3,000 miles which ever comes first, also at same time have all fluid level check, fuel filter and air filter replace once a year, tune-ups every two years, have your brakes check once a year, unless then feel funny have them check right away, transmission if fluid and filter has not been change every 30,000 miles, I leave it alone or new fluid will damage transmission clutches and transmission will have to be overhaul within 30 to 60 days.

The firing order is: 1-2-4-3

When seated on the motorcycle, cylinders are numbered from left to right 1-2-3-4.

your on the right track there its the starter relay you changed but you may also have a wonky starter
(ie: the starter motor brushed are worn out)

if starter doesn't engage, replace the starter.