Exhaust flow questions

[justanother54321]

I have a 79 GS850GN with rebuilt stock vm28 carbs, stock exhaust, revamped airbox, new air filter. New valve job, and valves are within specs. New dyna s ignition, wires and plugs.

I bench synched the carbs and set all pilot air and pilot fuel to factory/or whatever the carb rebuild series said. I will vacumm synch the carbs after finishing this posting.

Bike starts fine and holds idle at 1000 rpms pretty well.

However, when bike is warming up there is mild pop sound occasionally coming from the 3-4 cylinder exhaust.

Also, when placing my hand up to the exhuast pipes the 3-4 pipe is hotter and stronger than the 1-2 pipe.

My question is what could be causing this?

I may just end up answering my own question after I synch the carbs, however I wanted to ask now, in case I have trouble synching the carbs with manometer.

Any comments are always appreciated

[Nessism]

Sync the carbs before worrying about issues like this.

[C.V.]

Sounds like you are lean on 3 and/or 4. The "factory settings" are just a guideline to get you going, if you are just popping a little occasionally on warmup, you are probably pretty close. Pull your plugs and check the mix, you may need to richen it up a hair.

[49er]

I have a 79 GS850GN with rebuilt stock vm28 carbs, stock exhaust, revamped airbox, new air filter. New valve job, and valves are within specs. New dyna s ignition, wires and plugs.

I bench synched the carbs and set all pilot air and pilot fuel to factory/or whatever the carb rebuild series said. I will vacumm synch the carbs after finishing this posting.

Bike starts fine and holds idle at 1000 rpms pretty well.

However, when bike is warming up there is mild pop sound occasionally coming from the 3-4 cylinder exhaust.

Also, when placing my hand up to the exhuast pipes the 3-4 pipe is hotter and stronger than the 1-2 pipe.

My question is what could be causing this?

I may just end up answering my own question after I synch the carbs, however I wanted to ask now, in case I have trouble synching the carbs with manometer.

Any comments are always appreciated

The stock carbs for the '79 850's are VM26SS. If you have 28's fitted and are adjusting the pilot air and pilot fuel screws to the recommendations on the carb rebuild series, they will be slightly lean.
What did you do when you "revamped the airbox?"

Do your vacuum synch and re-assess. It's straight forward with VM carbs.