How to check for air leaks?

[mustangGT90210]

My '93 has had a very random erratic idle ever since I first opened up the carbs. Never had it running long enough before to know if it would have existed before me or not. Anyways, my idle will hang, drop, slide, shimmy, and do just about everything but hold steady when the bike is warmed up. But I can start it cold and it will idle great.

Also, after warm, when sitting at a light, I can adjust the idle screw and I'll find 2 points - idle is too low, but the revs always come back down when I rev it up to probably 5-6k (no tach), or it will idle at the right sounding speed, but when I rev it up the same way, the idle will drop maybe 1 or 2k and just hang until I slip the clutch out and then it falls back to normal. Wait 5 seconds and the bike revs back as if I'm twisting the throttle.

No, my cable isn't catching anything, and no, this doesn't happen daily. I'm thinking it's a vacuum leak of sorts. So finally my question in this matter - how can I go about checking for vacuum leaks, and where are they most common?

[jestercinti]

This sounds like it could be a combination of a lot of things.

1.  When was your last carb clean?  Not just a little seafoam or carb spray, but carb clean?
2.  My bike behaved strangely like this once, and my valve clearance was out of wack.
3.  Are your clamps that hold the carbs to the bike tight?  That's where most air leaks come from.
4.  You have older carbs.  There is also a little o-ring under the diaphram cover that causes havoc too if worn/missing.

Also, look here:  http://gstwins.com/gsboard/index.php?topic=41199.0

[project94]

one thing you can try is to spray a little starter fluid on the outside of the intake manifolds while the bike is idling. if the rpms increase a bit, then you know some air is being sucked in there.

[mustangGT90210]

This sounds like it could be a combination of a lot of things.

1.  When was your last carb clean?  Not just a little seafoam or carb spray, but carb clean?
2.  My bike behaved strangely like this once, and my valve clearance was out of wack.
3.  Are your clamps that hold the carbs to the bike tight?  That's where most air leaks come from.
4.  You have older carbs.  There is also a little o-ring under the diaphram cover that causes havoc too if worn/missing.

Also, look here:  http://gstwins.com/gsboard/index.php?topic=41199.0

1. Last carb clean (and left side rebuild) was 2 months ago
2. I've never had the valves checked... it's due lol
3. I think those are tight... but definately will check them out. Maybe spray some WD40 or something on them while its running or something?
4. That little o-ring comes with the rebuild kit (2 of em actually) so both carbs have new o-rings.

Looks like I'll start where the carb boots link up and go from there

[jestercinti]

Regarding #3, there is an O-Ring between the boot and the engine that will become hard and brittle.

More importantly, if the valves are not in spec, the carb will never tune true.  My bike would have a rough time starting in the cold, and stall when I approach a stoplight.  It overall would not run right.  Close, but not "right".  My exhaust valves were so tight that no feeler gauge thickness would fit.  Adjusted the valves, and wah-la.  Runs like a dream.

I'd suggest fixing this first.  Your problem might disappear.

[mustangGT90210]

When it comes into the budget I will. Currently I'm a broke college student just trying to make tuition, then I've got tires to put on this thing... How much does a valve adjustment normally run?

[jestercinti]

You can do it yourself.  Follow BaltimoreGS' video:  http://www.youtube.com/watch?v=jIL0eMzRPF8

[mustangGT90210]

That's all it takes to adjust the valves? Really? It's that simple?

That just leaves 2 questions then. Where can I get the shims, and the little compressor tool that looks like a sickle?

[jestercinti]

Shims = here or the dealer (some will swap old for new) or eBay. Once you know what size, post or go to suzuki dealer. I'm sure there are dealers near you in Bradenton/Sarasota Florida.
Tool = Motionpro.com. Mine was $20 or less i think. The suzuki GS version. Sometimes it's called a valve tool, other times it's a tappet tool.

[mustangGT90210]

Thank you very much! I've got a Suzuki dealer about 40 minutes away from here in south south south sarasota, but nothing I can't get to. I need to go get some exhaust gaskets anyway while I'm there