Two carb questions for '81 KZ1000 CSR

#1: When warmed up, bike wants to idle at 4k rpm. I can get it down to idle while stopped by leaving it in gear and modulating the clutch, but a couple seconds later it will rev back up to 4k. Not sure what that's about.

#2: Have MAC 4-into-1 exhaust (very blued), K&N 2-into-1 pods, and stock jets. Just bought the bike, have not touched the jets or pulled the spark plugs yet, but it's very likely running lean. Suggestions for jets?

Thanks in advance!

Dynojet makes a jet kit that eliminates a bunch of trial and error. The hanging idle is likely related to an air leak.

An air leak? Coming from where?

I assume you're referring to the Dynojet Stage 3 kit? www.dynojet.com/pdf/2301.pdf

Most common place for air leaks is the carb holders, where they mate with he head, where they mate with the carbs, and through cracks in the rubber.
There are a lot of discussion threads about all this.

How many of those potential air leaks would result in a 4k rpm idle? I suppose it's easy enough to identify if there's air leaks, less easy to identify if those leaks are causing the wonky idle speed, oui?

Ah ha! This sounds exactly like what I'm dealing with. I'll check it out once my tank returns from getting painted.

Also one carb being way out of sync and another could be a stuck spark advance.
Steve

BarnyardCoral wrote: How many of those potential air leaks would result in a 4k rpm idle? I suppose it's easy enough to identify if there's air leaks, less easy to identify if those leaks are causing the wonky idle speed, oui?

Any of them can cause this. They are not always so easy to find as you may think. If the carb holders are stiff or cracked, they are probably toast.
Definitely check the timing advancer for easy movement. Don't need any fuel for that.

One common way you may read about to find vacuum leaks is taking a fine misting sprayer full of gasoline and spraying around the carbs while the engine is idling at the race speed. I think this is really bad advice. Great way to collect on your fire insurance, IMHO.

A better way is to fine mist spray either water or 70/30 water and isopropyl alcohol - the engine will stumble if you spray water at the leak.

But 75% of the time it is the manifolds...

Sooooo the revving was caused by a throttle cable that was just a bit too short and keeping the butterflies open. Fixed. Still put on new carb holders.

Glad you have a good fix and the new carb holders are not money wasted. Good to have a known good set on your scoot. 36 year old ones don't pass that measure.

Right, better to have that peace of mind. Been replacing other rubber bits and gaskets as I've gone along too. Worth it since they're usually pretty cheap.