Kz750 twin carb / throttle problems

Okay so the auto rev up to 4rpm came back an hour ago. Even after I adjusted the cables and thought everything was okay. What I did find was a leak where the previous owner had tried to seal a cable going into the top of the motor. Its the cable going to the rpm gauge. It was leaking fluid onto my exhaust head pipe right where the cable meets the top end. Could this leak be my cause for the rpm rise? I will replace the cable which I think is the speedo cable correct? Because the other cable is the tachometer cable. I'm about to just send the bike to the mechanic and have them go through the carbs and cables again.

Schmeck wrote: What do you mean by raise the needles? Going through the top of my carburetor there is a ring that me nor the mechanic could get to . Is there a special tool for that ring ? My snap ring pliers dont reach it .

Yes, it's s special tool.

If it is coming out of the head it is the tach cable. The part it screws into has some replaceable seals that go bad, that may be what is leaking. They are not very expensive and easy to replace.
The speedometer cable goes to the front wheel.

Okay so I will have to get another tach cable ( mine has cuts and tears in it ) and another seal. And yes Koolaid the seals are very inexpensive. Probably the cheapest fix I have seen yet. I get the feeling this leak has nothing to do with my rpm spike. I messed with the throttle and cables and it did nothing to the rpm spike. So I am going to assume my problem is in the carburetor. I also sprayed the boots and the rpm fluctuated ever so slightly. I might have a potential leak in my boots. So I will have to gather some cash to get the seals, boots, special tool for ring and Maybe bigger jets installed while I am in there. Bounty Hunter you said size 50 pilot jet works for you , Should I go any bigger with any other jets and what clip position should I run on the longer jet to compensate for the lean exhaust? Thanks for the help guys

The parts you need to repair the tachometer drive leak are the parts marked 6, 7, and 9 in the diagram below. They are all still available from Kawasaki and the total cost is about $10 at Partzilla.com.

Regarding your bike's idle - 2,000 rpm is not idling; that is way too high. What happens when you set the idle at or near 1,000 rpm? Ed

Schmeck wrote: I also sprayed the boots and the rpm fluctuated ever so slightly. I might have a potential leak in my boots.

This is an absolute indication that you have a leak, which will also cause your high idle after warm up. Personally, I would not do anything else carb-wise until this is resolved.
From looking at the parts fiche, I would check the clamps (especially that the carbs are fully seated), the balancer tube, and where the boots bolt onto the head.

Ed, I tried setting the bike between the 1 and 2 and it has problems wanting to stay on . If I set it at 1000 rpm it would be about a minute before the bike starts trying to cut off . The throttle reaction time is not great at 1000 rpm either. At 2000 rpm It will stay on as long as I want it to. And yes Koolaid It looks like I will be replacing the manifold boots butting against the engine. Another question, the cylinder looking thing coming out from the middle of the crankcase below the carburetors. It has a tube connecting to the airbox also. Could this be a potential leak also? It has a tear where it meets the airbox. Is this a breather for the crankcase?

Also Ed, If I do have an air leak , I would asume that is why my bike wont stay on at 1000rpm. The extra air and less fuel would run the bike lean and cause it to want to shut off correct? So if my thinking is on track , replacing my boots and sealing everything should fix majority of my problems . Another thing guys, where do I get replacement boots brand new? Im only finding used ones or the boots for the 750 four cylinder.

You are correct – that little “L” shaped rubber tube (marked #18 in bottom drawing below is just a breather hose. It should not have an effect on the idle.

Your understanding of the effect of leaking carb holders (“boots”) is correct; they will cause very erratic idle at low rpm. With the idle set very high, the slides are open quite a bit so there is less vacuum applied to the carb holder leaks, but with the slides down as during normal idling the leaks have a noticeable impact on the bike running. I can’t say new carb holders will fix all the problems, but it should help the idle. Once the new carb holders are installed you should sync the carbs. If you replace the carb holders soak the screws that hold them to the cylinder head with Kroil or another high quality penetrating oil for a couple days before attempting to remove the screws. Otherwise, those screws can be VERY stubborn, and lots of folks have damaged the screws or cylinder head by not doing this. Also, be sure to use JIS type screwdriver bits on those screws. If your not familiar with JIS bits just ask and I can provide a good link explaining what to do.

Here’s a place that has New Old Stock (NOS) carb holders (they have a very limited supply). I have bought from them numerous times before and was always pleased. www.themotorcyclepartsoutlet.com/cgi-bin/store/index.cgi Just plug in the part number from the Kawasaki.com diagram below. Ed

I strongly suggest replacing those screws with stainless steel allen head screws. They work a lot better and you won't have to deal with JIS phillips screws any more. I get mine from Ace Hardware; they should have them in stock and they are not very expensive. Probably an M6 in diameter, not sure on the length.
If you don't have a JIS screwdriver an impact wrench can almost always get them out, but they will not be re-usable after that.

The carburetors On my bike were soaked for days already and all jets and seals replaced. The longer screw from the top of the carburetor with the clip is the only thing not messed with. The floats were replaced and carbs should be spotless because I have to fuel filters and the gas is clean with seafoam in it. I should have taken a photo of before and after of the carburetors. They are fully restored ( for the most part) . I think once I change out the boots N breather tube I will just do a quick clean of the inside . While I am in the carburetor though, is there anything I should change . Everything is set stock except my idle screw ( its at 2000 rpm like i said before) . Clip position ? I would like to adjust for the tailpipe.

On another note for peace of mind , I am going to clean out the tank again . I might use evaporust ( which is expensive). On the other hand, if I use muriatic acid, Can anyone suggest a better way to seal the tank to prevent unwanted rust? Thanks for the help, and thanks Ed for the website to get the boots.

If you don't have JIS screwdriver bits, they are REALLY easy to make and will let you remove the screws with little problem and reuse the screws. Take a look at this link. BTW, I ground mine just using a coarse whetstone rather than a powered grinding wheel; it took less than 10 minutes. Ed

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