81 GS1000 jetting for 4 into 1

[bforster199]

I am installing a V&H 4 into 1 header on an 81 GS1000 and need to know what to re-jet carbs to...header was bought used and came with no jetting instructions..."falls flat on its face" around 5500 to 6000 rpms....any help is much appreciated...thanks

 

[tkent02]

Do you have the stock intake system? Stock engine?
Are you somewhere near sea level?

 

[Guest]

I'd put in a 122.5 main jet
Shim the jet needle
Take out the idle mixture screws a bit

 

[bforster199]

Intake is stock and motor is stock....located in Michigan

 

[tkent02]

Go with what Chef says. Better yet go one size richer on the main jet, he likes to burn holes in pistons.

 

[twr1776]

bforster199, I agree with Chef and would also suggest possibly bumping your pilots to 42.5. Maybe pick up the 120, 122.5, and 42.5 pilots before starting your project so you have them on hand. The Mikuni jets are only about $ 3 each last I checked. I am currently running a stock airbox with a K&N filter, 120 mains, shimmed needles, and the 42.5 pilots on my 1000.

All bikes are not the same even within motors but that should get you close enough to fine tune from there. If you have not done it yet I would also suggest adjusting your valves, replacing intake boots and o-rings, replacing the airbox to carb boots, replacing exhaust gaskets, and sealing your airbox before even starting on your jetting. Unfortunately there are no shortcuts to proper jetting so if you have any intake or exhaust leaks you will not get accurate plug reads and it will be very difficult to get it to run right.

 

[bforster199]

thanks alot guys....your input has helped tremendously....i can move forward with the re-jetting project now...thanks again!!