GS650 Mikuni BS32SS synch and tuning question

[Guest]

Howdy folks.

I got myself some actual pressure gauges with dampers installed in them, and set them all up. They look nice. I can get the gauges synched - but once I have them all synched, I can't get the idle to drop down to where it should be.

Valves adjusted, carbs rebuilt (all new o-rings, cleaned thoroughly), new carb boots, new plug wires.

I'm pulling about 10psi vacuum on the center two, and as I understand it should be pulling slightly more on the outsides - meaning the outside two butterflies are more closed than the inside two.
Right now, It's hovering at 10psi inside, and about 12 outside. However, I keep backing out the idle screw and the idle doesn't drop.

Closing a butterfly on one of the outside carbs beyond a certain point actually raises the engine rpm.

I've also played with the highest idle mixture screws, and I think I have that dialed in. But this is a bit fiddly, and I am not so good with fiddly things.

Maybe I should do a compression check before I try to synch the carbs.

Thoughts?

[81GS850]

There is an idle screw in between 2 and 3 that controls 3 throttle blade opening. it should be accessable between the air filter and carbs. That's probably open too much. What RPM are you at now?

[WilliamGLX81]

Woohoo! I got it. I uh.... may have had the engine a little too hot

Carbs are synched! Can't wait to ride it tomorrow. It also sounds waaaay better.

[Steve]

Maybe I should do a compression check before I try to synch the carbs.

Thoughts?

Skip the compression check.

Any chance that you adjusted the valves before doing the vacuum sync?

If not, let the engine cool overnight, check the valve clearances.

If you have to change any of them, you will have to re-sync the carbs.

.

[WilliamGLX81]

I did the valve clearances by changing shims last fall or thereabouts. Only put a few thousand miles on it since then.

[Steve]

Only put a few thousand miles on it since then.

Depending on which manual you follow, they should be checked every 3,000 or 4,000 miles.

.

[WilliamGLX81]

Hmmm. All the more reason to get my speedo/odometer working again. Got to buy a new (used) drive unit. I got creative trying to fix my old one ... and it worked for all of 2.2 miles :P