1983 GS1000G surging around 3000...3500 rpm?

[Finn]

Cheers!


Soo, I have slowly but steadily gotten the GS on the road. One crucial detail was to have carbs ultrasonic cleaned and checked for possible strange jettings etc.
Everything was OK, just idle jets clogged. Jets etc. were stock sized and everything was mechanically OK. I got new manifolds and O-rings so there are no leaks. And jets and needles are stock ie. no jet kit present.

Everything works really nice but I get some degree of surging or such around 3000...3500 rpm with steady throttle on the highway. Anything below that works really nice and it pulls to redline if needed. Just the said surging (or slight bogging) is bothering me.

Here is the list of done things:
- carb cleaning as mentioned above
- new spark plugs and caps
- valve clearances adjusted to factory spec
- cleaned and oiled air filter in stock airbox
- gas gap venting passages cleaned and now open
- new OEM petcock
- new fuel and vacuum hoses
- probably something else I'm forgetting

Is this surging (or slight bogging) typical for these?

If it is what would you suggest for correction?

Raising of the needles with one or two washers would be easiest thing to do. But I will leave any of this work for the gentleman, who did the carbs for me, as he is familiar with carbs.

[Dogma]

Are the carb vent lines routed to the still air behind the airbox?

[Nessism]

How are the foam seals on the end caps of the airbox? If they are leaking, which most are unless refreshed, then it can cause issues like you describe.

If the foam is bad, get some weatherstrip foam from the hardware store and go to work.

And FYI, to lift the needle you need to reduce the thickness of the plastic washer on TOP of the needle. Sticking washers under the needle does nothing. Remove the needle and you will understand.

[Finn]

Are the carb vent lines routed to the still air behind the airbox?

Yes, they are routed as you describe.

How are the foam seals on the end caps of the airbox? If they are leaking, which most are unless refreshed, then it can cause issues like you describe.

If the foam is bad, get some weatherstrip foam from the hardware store and go to work.

And FYI, to lift the needle you need to reduce the thickness of the plastic washer on TOP of the needle. Sticking washers under the needle does nothing. Remove the needle and you will understand.

Said foam seals were toast just like the one on the air filter top surface. I replaced all those with suitable materials and they appear to be OK now.