Topic: intermittant # 3 & #4 running?

[birdy]

Ok- I start her up and only runs on#1 & #2. Hold throttle to keep running (I've already turned throttle screw up), rev her up and finally #3 & #4 kick in.
Go round the block engine revs nicely until after a slow 30/40 mph cruise - I come to lights and it's back to #1 & #2 only again. Limp home on 2 cylinders.
Not the coils due to pairing order - can it be fuel to carbs, but why only now and again?

[donny]

yes....I would look at fuel issue,  since 3-4 share a fuel line.. ..
       1 )  float levels ? ?
       2)   semi plugged fuel line to 3-4 ?
 

[tlbranth]

Clean the petcock and try removing line filters if you have them.

[my78k]

What bike? Is there 2 separate fuel lines or shared? When were the idle jets cleaned?

Dennis

[TwoTired]

What do the spark plug deposits look like?
When was last tuneup check list completed?

What is the cleaning history of he carbs?