81 KZ900 with smooth bores. idle too fast

Bear with me. My son has a highly modified 81 KZ900J with older style smooth bores. I'll get the manufacturer when I see the bike. He just told me that it is not running right. Idle is too high, even though idle adjust screw is all the way out. He says there is free play in the throttle pull cable. Only has pull cable. He also complained of cutting out at high speed but only under load.

When I say highly modified I mean it has an 1100 kit, Dyna rev limiter, cams (degreed) by a pro engine builder) 4 or 5 years ago. Up until recently it has run like an absolute beast. Now last summer it started to run real rough while we were on a road trip. Got it home ok and I swapped in two coils from a CB900 I had and that fixed it. Now after the winter lay up this just started within the past couple of weeks. He has been riding it once or twice a month up until about 4 weeks ago where he now rides it at least 2 or 4 times a week. And it's been getting progressively worse each time he rides.

So we both thinking maybe it;s going lean because of a vacuum leak but I'll be darned if I can find it using carb spray. It has pod filters and the carbs were tuned, by that same pro engine builder when he did the engine work a few years ago with those pods. My son told me it gets only slightly better if he adds a little choke but then runs too rich.

So after all of that long wind story I'm after a few suggestions about where to start or more to the point what are the usual suspects. I'm thinking first thing to do is pull the carbs and engine insulators and give them a close visual inspection. Secondly it has a couple thousand miles since the rebuild and we need to check valve clearance.

Any other ideas?

I'd check the valves first.
Steve

Thanks Steve,
Actually I need to replace the valve cover gasket and the cam plugs so I was going to do it all about the same time. But I like your idea. Once I get the valve cover off and the cam plugs changed, I can leave the carbs hooked up to do all of that. Then once I shim them, if needed, I can just button it up and do a test run. If the problem still exists with high idle well I've already got the tank off and can hook up the sync gauges to see what I have. Spark plugs are new but I can certainly pull them and run compression and leak down tests. If i'm that far into it might as well just check everything I can. He only rides it on the weekends and if needed he can borrow my KZ1100.

I am enjoying the heck out of my retirement.. Get to play with motorcycles all day!

Valves were all within spec so no issue there. All measured about .10 mm.
Here is a pic of the carbs I'm dealing with. Remember this is a built engine and until the last couple of weeks ran well. The carb holders are not original to this bike. It came with BS34's no vacuum port on the holder. If I have to get new holders do you have a suggestion? when I pull the carbs, later today, I'll measure the OD of the carb throat. I think they called these 29MM smooth bores... Maybe 28mm.

Just because I'm proud of his painting skills:

Those are 28's. Not smooth bores. Good carbs and holders are easy to come by.
Steve

Thans Steve,
I just measured the interior diameter of the throat and showing 29 mm OD is 33.7 mm but I think it's a mute point as the carb holders are like new. Still flexible and soft and show no signs of cracking. Now I guess I'll put it back together and check sync. I did notice that two of the cheap Pods he put on were virtually falling apart.The filter elements just fell off when I grabbed them to remove. That could be my problem but even if not I'm replacing those cheap ass pods with some good ones. Poor kid put this bike together when he didn't have any money.

In any event I think I should take the float bowls off and just make sure everything looks ok in there. I'll clean the idle and high speed jets and circuits. The bike usually sits for sometimes up to 3 months at a time in a heated garage. I'm starting to get stumped as to why the high idle. Hoping the sync gauges will give me a hint.

The holders may look good but where the fit on the head gets hard an small cracks develop. If that's the case, new ones are in order. You can seal them but it's only temporary.
Steve

There is a lot of "varnish" looking stuff under the holders and I haven't gotten around to cleaning them yet. I just put the carbs back together, found nothing other than one float needle springy top isn't as strong as the others but some brake cleaner seemed to loosen it up, if it was stuck a little. But setting the floats "static" they are all the same when I rotate the carbs so the floats just touch the needles. Hunting up some clear plastic tube for a level check to be sure. Even though I'm not finding anything wrong at least I'm eliminating things.

The "varnish stuff"suggests leaks. I used :ohmy: Permatex to seal my old ones. It worked until I could get some new ones.
Steve
www.diablocycle.com/Carb-Holders-Kawasak...1100-PM14-94001.html
www.z1enterprises.com/product/IMK16065-028-K
z1parts.net/z1900-kz900-kz1000-manifold-carburetor-holders/

Steve, any idea what part number I should be ordering for those carb holders? Maybe from a 78 kz1000? The carb holders I have now have a couple of markings. An "R" for the right side and 'L" for left two. Also has a "022" on the outside edge that goes toward the carb throat ID also measures 32mm where the carb would go in. On the output side it measures 29mm ID throat and the screws are 58mm center to center.

Here's a set. I don't remember having any fitment problems but that was a long time ago. 26, 28 and 29's will fit these holders. You may have to open the insides to fit the bores diameters. What was wrong with the CV carbs?
Steve
z1parts.net/z1900-kz900-kz1000-manifold-carburetor-holders/

Thanks for the url. There was nothing wrong with the CV carbs. When my son bought this bike it didn't run well. I think #2 and #3 were low on compression. Well we know Doc. Dale Stewart who builds Kawasaki Race engines and he needed a drag bike painted. My Son paints for a living so they swapped their time and parts. My son did a custom paint job on his dragster and Dale built the engine and he stuck the 29's on there. It is an 1100 now and It is an absolute beast when it's running good. I have never had the guts to take it to full throttle. It is that scary fast. I've seen my son roll the throttle on in 2nd gear and smoke the rear tire. Well I made him put a new tire on the rear that has a little more grip but he still smokes it at will.