Slides at Part Throttle, KZ440

I'm trying to smooth out a part throttle surge condition. It feels like a massive vacuum leak when riding. The bike starts and idles great. When you pull the throttle wide open, it pulls like it should right up to 9g's. I've cleaned the carbs, checked the slide diaphragms, checked timing and advance, replaced the points and condenser (the bike came with them), adjusted valve lash, added a fuel filter.
It's a 1980 KZ440 with 15,750 miles. The stock air filter is missing, but the air box is there. I fabricated a filter setup that uses 7/8" ID breather filters.
The left plug is white, the right is dark. I have observed the slides through the air box with the filters off, and they will snap up when I open the throttle wide open. Today, I noticed the slide doesn't move at part throttle, 4,000-6,000 RPM. It seems like it should move some at this throttle position to allow more fuel into the mix. Am I wrong? Should the slides only move at wide open throttle? I'm thinking this is my problem, but I'm sure that your knowledge and experience will help me verify this or I'll look for something else causing this.
Also, I know I need to replace the intake boots/carb mounts. I don't expect that to fix the cruising surging issue altogether, but it might help. Maybe I'll get lucky, though, and that will solve it. Thanks in advance.
-Bob

bobrpm wrote: ...............The stock air filter is missing, but the air box is there. I fabricated a filter setup that uses 7/8" ID breather filters....

IMO you are wasting time fiddling with it any further until you install the stock air filter in the air box. Home made stuff is not the same. After the stock filter is installed you can much more easily identify the problem IF a problem still exists. Ed

Is it a 440 Ltd? there are 2 different 440 airboxes & they use different air filters. see diagrams at partzilla.

Note: treat the airbox with care, especially the cap. Don't overtighten the screws or force anything. Also, on at least one of the airboxes, it's possible to install the cap wrong. If not done properly, this causes a vacuum leak. The test is to pull up gently on the back of the cap. it shouldn't move. (info from Andy-the-gringo).

Thanks, guys. When I got the bike, it was equipped with two chunks of what looks like couch cushion foam in the rectangular ports on the air box. I've looked for a factory filter housing with no luck. I'm going to replace the carb mounts/boots and see what happens. They need to be replaced anyway. Even at the 4,000-5,000 rpm range it smooths out some when I sprayed starting fluid on the boots. It will run pretty good in neutral. Revs nicely with snappy response right off idle. When I ride it, it struggles. I know the vacuum signal is reduced under load since the throttle is opened more at a given rpm. It's probably drawing too much air through the boots. I know a homemade filter setup is not ideal, but I'll have to play with it until I find the best setup I can for maintaining the correct vacuum for the carbs to work right. Thanks again.
-Bob

Bob, you really need to identify which model motorcycle you have if you expect to receive the best help others can provide. Kawasaki made 3 different 1980 KZ440 models. You haven't said if your bike is a 1980 KZ440-B1; KZ440-A1; or KZ440-D1. As Martin pointed out they do NOT all use the same air filter. Example:

Yeah, sorry. It's an A1 LTD. It's missing the whole filter assembly (2,3,4). If the slides should be moving at part throttle, then I more than likely have a vacuum problem. That could certainly be due to the air filter setup that is currently employed. If they aren't supposed to move at part throttle, then I need to chase something other than vacuum as the issue. I should have a chance to work on it again in a couple days. I'm just wondering if the slides should be moving at part throttle so I can narrow down whether the problem is vacuum related. I'll also hook up a vacuum gauge and check the signal at various RPM and see how much it changes with the starting fluid sprayed on the boots. Thanks again. I appreciate your help and patience.
-Bob

Replace your carb boots first.


.

Okay, I've been busy, but the carb mounts came in. OEM from cycle-parts.com for about $80 shipped. I'll work on removing the old ones and getting Allen bolts. Should I use a sealer between the mounts and engine? And does anyone know the size of the bolts? Again, 1980 LTD 440. Thanks.

No sealer. Regarding removing the old bolts I strongly suggest 2 things:

1. Soak them bolts with Kroil for 3 days prior to trying to remove them. I did this on mine and they came out with no struggle at all. Kriol will break the bond between the bolts and the cylinder head. Believe it or not, some folks have actually broken teh cylinder head trying to remove carb holder bolts that have bonded to the head. I re-applied Kroil each day for 3 days and the bolts easily came out.

2. Assuming they are the original bolts you need to understand that they are NOT Phillips heads even though that's what they look like. They are Japanese Industrial Standard (JIS) and using a Phillips screwdriver with deform the crossheads and will very likely make them nearly impossible to remove. Take a look at the following 2 links for details about how to make JIS screwdriver tips. Ed

www.kzrider.com/forum/search?query=newbi...0/2017&childforums=1

www.kzrider.com/forum/search?query=homem...0/2017&childforums=1

Thanks again, Ed.

Update: I got the new mounts installed. Didn't make any difference, but the old ones were definitely bad, so no loss. I realized that I cleaned the main and needle jets and passages but not the pilots, so I cleaned them out. Thought maybe they were flowing enough for a smooth idle but not enough for the transition from the idle circuit to the main circuit. No dice!

I narrowed the problem down to the right cylinder based on exhaust temps. Spark showed well at various RPM on both cylinders. I switched the the wires, then the plugs. The problem stayed with the right cylinder. Fearing the worst, I did a compression test. Both cylinders pushed 165psi. Awesome!

At this point I'm thinking I'm going for the mikuni single carb setup. I just want to be certain it's the carbs before I go that route. So, I observed the carbs through the air box with a flashlight.... again. Gas was flowing from the needle jet in the left carb and flying out on the right carb. That's when I realized that the right carb is missing the silver cylindrical thing that the needle goes into. Hmmm. Got one coming for $12 on eBay. I bet this part will meter the fuel coming from the needle circuit and my problem will be solved. Should know this weekend. Thanks again.
-Bob

After looking at the FSM diagram, I see that this part is the needle jet. I thought the secondary main jet was the needle jet. Obviously, running with no needle jet will flood that cylinder when the slide rises. I'm pretty sure replacing this will solve the problem. I'm guessing that the needle jet is just pressed into place. I'll find out this weekend. Cheers.

Sounds like you found the problem. Running with no needle jet certainly would make the engine run poorly. Ed