81 KZ750 LTD Starting Problems

I have searched this forum and could not find a problem exactly like I am having, so maybe someone out there can help. Here goes...

I recently completely cleaned my carburetors, re installed them and the now my bike is very hard to start. Once started and warmed up, it idles great and runs awesome. I did detect a leak in one of the carb holders, so I ordered new ones and installed those. Still same problem. Is there something that I maybe did when cleaning the carbs? Or should I keep searching for more vacuum leaks? Ignition problem? Petcock problem? After cranking for a few minutes, I pulled a spark plug and did not smell gas, so that leads me to believe it is in the fuel delivery, but maybe I am wrong. I do have the Clymer manual and it doesn't address this issue.

It has been cool here-around 40 degrees, but today it was over 50 and still the same problem.

I have to add, when I bought the bike last fall, it started really good. The only reason I cleaned the carbs is they were really dirty on the outside, and when I drained the float bowls there was particles floating in the gas.

My bike is a 1981 KZ750 LTD with the Keihin CV carburetors.

Just some thoughts before the experts jump in.

Can you verify that you are getting spark at the plugs ?
Cab you verify that the carbs are getting fuel ? Perhaps open the drain screw and see it gas flows out - keep a can or bottle underneath !
Did you remember to put the vacuum caps back on the carbs after cleaning ?

If the plugs are dry it does sound like gas is not getting to the cylinder and it could be something you did while cleaning.
How did you clean? First time I ever cleaned carbs I had to do it about 3 times and it was only when I used a nylon bristle to poke through every hole I could find and satisfy myself that every passage was clear and then blow through everything with compressed air that I had success. You might just have dislodged a minute piece of dirt that still need to be cleared.
Good luck.

If it runs well once warmed up but is hard to start then I'm guessing it is a choke problem. Do those carbs have an enrichener circuit or just a butterfly that closes when the choke is on?? When I cleaned my BS38's the first time I neglected the enrichener circuit and had a similar problem. I took them off 3 more times to clean them and I'm still not happy with them so like JR said I'm taking them apart again this spring to clean them with a brush and compressed air. Hopefully this time it will work.

I have the Keihin CV carbs on this bike. It does not have an enrichener, just a butterfly choke.

Yep - just the butterfly or flap on the Keihins. Sounds like the pilot jet plugged and they do plug easily. You will find it under the little neoprene plug once you take off the bowls.


good luck

Wouldn't the idle be off it the pilots were plugged? Once started and warmed up, it idles good and runs great all the way up to full throttle.

You know, you could be right
I may have made a hasty call there regarding pilot jets

Anybody else out there have any ideas? It does start with a very quick shot of starting fluid in the airbox.

The carbs haven't been synched since I have owned it, could this be the problem?

You can check the rubber diaphrams for small holes or tears.

I just replaced the rubber boots going from the carb to engine. And the boots going to the air cleaner look good.

I don't know if this will help you, but I've recently had a bit of trouble starting mine. Too many kicks, then a backfire and starts Decided to take a look @ the plugs, before starting it. Eventhough they looked pretty good there seemed to be a bit of carbon on the electrodes. Took some 600 grit sandpaper and just lightly cleaned them up. Put them back in and it started on 1 kick, after setting a week. I've thought I may be running a bit rich, and this seems to have proven that. Gonna go down a size on my pilot jets and see if that clears up the slight carbon issue

I have tried new spark plugs. I even put in one step hotter since it has been below 50 degrees.

Maybe that is my main problem, once the weather warms up, maybe it will start better.

I purchased the bike last fall, and it started really well, until I started cleaning the carbs. I cleaned them thoroughly. I work at a cycle shop and was able to use their ultrasonic cleaner. Maybe I dislodged some old junk built up over the years.

Like I said before, once it is running, it idles normally and runs strong all through the RPM range.

Any other ideas are appreciated. Thanks for the input. This forum is great.

Chuck