Yes, the first suspect in such a scenario is an air intake leak resulting in a high idle from the lean mixture when the engine warms up. Make sure the airbox is sealed tightly. You may need carb boots or intake O-rings.
First - apologies for the brief hijack, but it might be of some help.
This thread was a timely find. A couple of weeks ago I bought an '81 GS1000G, that had just had the top end of the motor gone thru (honed cylinders, new rings, valves lapped and new guides & seals). Quite a craigslist find for $995.
The only real issue with the bike, was an apparent rich condition (poor mileage, fuel smelling exhaust), and an idle that climbed to 2500 rpms when it got good and warm.
It fires immediately from cold with no choke, and the idle speed is normal until you've gone a few miles.
I began to dig thru the archives of wisdom here and and elsewhere, and started on my list of things to check. I started a thread on AdvRider.com's The Garage subforum, and a few knowledgable folks from here (bwringer most notably) pitched in with tips.
The bike is completely stock with the exception of a K&N filter element.
There was no apparent leak or bad clamp connection in the intake boots between the carbs and airbox, and the intake manifolds were replaced during the top end work.
I removed the airbox, and the filter - and saw that the foam seal between the element and airbox was in bad shape. Rotten foam, mashed flat...and chunks at each end were just missing, letting unfiltered air pass.
I'm hoping this is the culprit.... as I dug further into it and couldn't find anything obvious. I replaced the seal with self-adhesive foam weatherstripping, and it seals fine now.
I removed the carbs and checked the o-rings at the intakes - all good, and the screws were all tight and the seal looked good and even all the way around.
The PO had a local privateer shop do some carb work, so there was an unknown I needed to check out. He said they'd rejetted for altitude and synched the carbs. I've never needed to rejet a CV carb for my 6,000 ft altitude - though the richness had me wondering what they might have done.
Main jets were stock 115's, pilots were stock 40's, the needle stock, and the diaphragms looked like new.
The floats were the correct height (22.4mm), and the float needles and seats looked as good as new. The float bowl gaskets were pretty bad, and had a layer of Hylomar or some gasket goo keeping them from leaking...so I'm waiting for a new set from Z1.
The carbs checked out fine, and looked so new....I was running out of ideas.
Seeing this thread gave me hope that the airbox seal was the cause.
I went ahead and ordered a petcock rebuild kit just because the rubber parts are so old, and the amount of grief a crankcase full of fuel can cause. It doesn't leak now, but...
And before I take it far from home, I will likely do the Electrosport stator and regulator/rectifier. Cool bike though....my 41st since 1968.
