1981 KZ 750 LTD Idle Issues

Hi again!!! I am having issues with the idle on my bike. I have replaced the entire igntion and fixed one problem, but now I have another. I bought the bike used and it would only run with the choke on. And now even with the choke on it idles aroung 2500 rpms and then idles down until the engine dies. I have replaced the plugs and wires. The ignition coils are firing fine.

I thought maybe the issue was where it had been sitting waiting on ignition parts. I got them yesterday and took the bike for a 25 mile ride. I then noticed a small miss in the bike at idle and as I initially hit the throttle. After that point the bike clears up. When the ignitionis turned off, the bike backfires.

The bike has the Vance & Hines Magaphone exhaust. I am not sure if the carbs were rejetted or not. Could this be the reason the bike will on idle with the choke on and maybe the source of the miss also.

Some 750 4cyl models came with Keihin CV34 and some with Mikuni BS34 carbs. I THINK your bike came with the Keihins. You might want to verify as the carbs are pretty different in some regards and there are model specific differences that can cause the idling issue. I am thinking though that perhaps you should look at air leaks before going further. Might not really be the carbs, per se but air leaking in via the intake manifolds or the vacuum cap(s) on the carb bodies. Is the emission stuff still on the bike? If that junk is leaking, the bike's idle will be affected. The common advice is to spray some WD40 around the carbs as they idle... if the bike stalls or spits white smoke, they are surely leaking. It is also VERY possible that the mixture screws are leaking air if the orings are old. Both types of carbs handle orings differently.

I suspect that the first step will be to pin down which type carbs we are talking about. Then I can be just a bit more specific.

You are correct the bike did come with Keihin Carbs.

I took the apart today and cleaned all of the jets and the carb body itself. I rechecked all of the clamps on the carbs and also the rubber tubes that run from the air box. No leaks there. The cleaning gave the bike more power, but still didn't fix my issues with the bike missing and having to run the bike with the choke on. The only thing that I did not mess with was the air fuel screws.

Remove the mixture screws and springs. In the wells where they sat will be little bitty washers and under the washers will be little bitty orings. Replace the orings. I would also go ahead and replace the intake manifolds even though they look OK to you. Those things should be replaced every few years as they just harden some and won't seal as well as they should. Also, is the emissions stuff still on the bike? Also, remove the #35 Keihin pilot jets. There are no replacments so be gentle with them. Clean them good and spray carb cleaner through the pilot circuit.

Post edited by: wiredgeorge, at: 2006/08/27 08:44

I pulled out the idle screws and to my surprise there were no springs. I never got to the point of the O rings. I turned the crews in till they were seated and then backed them out two turns. This helped the idle, but without the springs, the screws back out on thier own. Is there a place to purchase jsut the orings and springs on will I have to purchase the entire rebuild kit???

Any ideas on the bike not idling unless the choke is fully on??

See: www.z1enterprises.com/detail.aspx?ID=475

Make sure you use a pick and get any old oring out from inside the well that the pilot screw was in... I know of no source for the springs.

The K&L kit for our carbs comes with the spring, washer, O-ring, pilot needle, and a cover cap. They are 15 to 20 bucks per kit. Kit also includes a float needle, float bowl gasket(O-ring type).

Don't loose any of the parts because there are no extras. I spent a lot of time looking for those tiny parts that I dropped, while being carefull not to drop any of those tiny parts. They hide very well.

Like WG sez-- Z1 is a good source for the kits. There are others.

1981 KZ750-E2

The K&L kit for our carbs comes with the spring, washer, O-ring, pilot needle, and a cover cap. They are 15 to 20 bucks per kit. Kit also includes a float needle, float bowl gasket(O-ring type).

Don't loose any of the parts because there are no extras. I spent a lot of time looking for those tiny parts that I dropped, while being carefull not to drop any of those tiny parts. They hide very well.

Like WG sez-- Z1 is a good source for the kits. There are others.

1981 KZ750-E2

I just found out that I am missing a spring in one of mine as well. Went to bikebandit.com and put in the part number that I got from kawasaki.com, and they had the spring only. Also ckecked the orings, and they sell those too. $3.04 for the spring and $2.65 for the orings. You may want to get you part numbers and check bikebandit. Would be cheaper than the whole rebuild kit.