1982 KZ750- Help!

So I have an '82 kz750E3 that, until about a week ago, ran great. I fixed it up after buying it for $300 in pretty rough shape. I've maintained it well, etc.

Last week I finally installed a real carb-rebuild kit to eliminate a couple nuisance gas drips. Since then, I've had a problem that's been getting progressively worse.

The bike runs fine cold. It idles at around 1100 RPM smoothly, throttles up fine, and returns to an even idle. As the bike gets hot (highway riding, for example), I begin to lose my even idle. What I mean is, I'll clutch in at a stoplight or something, and my idle will hover, race, or roll off and stall the bike. Sometimes I'm lucky and it'll stay at about 1200, but that's becoming very rare.

I pulled my carbs and petcock apart just to make sure I wasn't flooding or starving any of the carbs. I blew out the jets, backflashed the seat screens and filter, changed vaccuum lines, checked gaskets, WD-40'd the heck out of anything moving, checked my plug gap, made sure my electrical connections were secure and clean, etc.


Last I checked, I had an even 160 PSI across all four cylinders.

My attempts didn't change a thing. It still runs fine cold, and dies/hovers/races at idle when hot. Still does fine on the highway, but downtown seattle wasn't much fun.

My only two thoughts are:

a) The plugs that insert over the pilot jets all fit snugly except for one. One of them doesn't have a PERFECT seal. Could I be running an overly rich mixture at idle?

b) I swapped out my air screws during one of my many recent carb-rebuilds. The two on the right hand side were set at the stock 2.5-3 turns out. The left two carbs both had the screws seated. I set all of them at about 3 turns CCW from a seat. It acts sort of like a lean mixture (hovering idle), but the fact that it's getting worse every day tells me it's something deteriorating, rather than an adjustment.

Am I right in thinking that it sounds like a fuel system issue? I'd guess that my coils might be the problem, but then I wouldn't have such erratic behavior at idle...

If anybody has ANY ideas, please let me know... I just want a reliable commuter bike, which this was before it turned to the dark side... ugh.

Thanks for reading my long post, and thanks in advance for any thoughts you might have,

Casey

Welcome to the site. Nice bike you got there.

Those plugs over the pilot jets should be snug. When you got the rebuild kits did you notice an O ring which would fit the plug. Tight fit I should add but it works.

With the air mix screws at 3 turns out what colour are your spark plugs. Are they white ?... which would indicate lean. I always thought 2 turns out was stock but doubt an extra turn would make that big a difference.

I think with all the rebuilds your carbs could do with being synchronised.

Final thought is that you guys in the US got all this emmissions tubing coming out of the valve covers and going all around the place and I hear it can be a PITA If you have this stuff then consider getting rid of it. Take one vacuum line from carb to petcock and cap the other 3 carb vacuum nipples. With the stuff coming out of the valve cover I think people just run tubing from one side to the other but best wait for an expert to come along.

Where are you located ? I'm guessing US but you could be anywhere on the planet.

Thanks for the reply, JR. It's a great site, and I like what I've seen so far. I bought it in semi-running shape. Cleaned the carbs, repaired the leaking exhaust header gaskets, pulled apart my timing unit, brakes, etc, and sprayed her down with a quickie rattle can job for about twenty bucks. I liked the result for such a rushed fix-up, and its a very reliable bike, until now that is.

I'm in the US. Washington state, more specifically.

Two turns out on the air screws might be correct. I suppose I shouldn't assume that anything on my bike is stock. I'll give that a shot. My plugs have been a nice tan/grey, which I liked, but I haven't run the thing much since setting the screws. I'll give those a try.

I did see those nice little, undesignated O-rings in the rebuild kit. Thanks for steering me in the right direction for those. I'll try them as well.

I haven't run a manometer across the carbs to sync them, but I've synchronised the butterflies by shining a bright light down the barrels with the slides removed. I haven't really checked them out recently, so I'll do that too. Good call...

And are you describing the PCV valve assembly? Two tubes from the top of the valve cover running to a valve that connectst to a carb vaccuum? I haven't messed with it, but I'd be surprised if it had such an effect. Nevertheless, I'll see what blocking it off and closing that carb nipple does.

Thanks again. I'll keep you updated.

charwood89 wrote:

And are you describing the PCV valve assembly? Two tubes from the top of the valve cover running to a valve that connectst to a carb vaccuum? I haven't messed with it, but I'd be surprised if it had such an effect. Nevertheless, I'll see what blocking it off and closing that carb nipple does.

Thanks again. I'll keep you updated.

Yes. That's the stuff. We did'nt get that up here in Canada but I read a lot of posts on the site here which say that if you have it get rid of it.
Anybody out there care to jump in on this ?

In the rebuild kits are a couple of O rings. The tiniest ones go with the air mixture screws and the next size (I think) are for those plugs.

I really think you would benefit froma proper carb sync with a manometer.

Just another thought - have you got an inline fuel filter ?

Good luck



Just another though

I do have an inline filter. It had some gunk in it, but I backflashed it pretty thoroughly with carb cleaner to clean it out.

Good news. Replacing the O-rings on the pilot jet plugs seemed to do the trick. I'm idling smoothly at 1000-1100 whenever I clutch in. Thanks for the help!

I'll certainly make a point of synchronizing my carbs and getting rid of the PCV assembly. I don't have a manometer, but I do have a vaccuum guage. If I go across each carb in turn, starting with the primary, I should be able to balance them well enough, right?

Thanks

you need more than one gauge:(

SPARKY47 wrote:

you need more than one gauge:(

Absolutely.

As you adjust one carb it will upset the others. I dont think it would be worth the bother of trying with one gauge.

Glad to hear you got the idle sorted out