81 KZ750 LTD Starting Problems

the rubber diaphrams I speak of are under the covers on top of the carb. They are attched to the slide in the carb.
Did you take these out when you used the ultrasonic cleaner?

Yes, I took those out and cleaned them. They were dirty, but in good shape-no tears or holes.

brox wrote:

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?

No. Hard start cold and good running hot is a classic lean condition. The choke is not riching the mixture enough.

Just a thought: when you crank it to start it, do you close the choke and leave the throttle CLOSED? If you open the throttle as you crank, the choke doesn't work.

ronjones wrote:

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

Good point. gas is a great solvent, and if your plugs are fouled: the "cranking time" is needed to get enough gas on them to clear the tip enough to fire.

Try cleaning the plugs and seeing if it still hard starts when cold.

Thanks again for all the help. I will try the spark plug thing tonight. If it is running lean, where should I start looking? Is this a pilot screw adjustment, or larger pilots? I did install the Kerker header last fall, and it was running good, but I didn't check to see if it was running lean.

I checked the spark plugs and they were dry after cranking for a few minutes. I also turned in the pilot screw to try and get a richer mixture. What would the next step be, pull off the carbs and check the pilot jets? Thanks for the input.

You are leaning the pilot mixture when you turn it in. Your pilot jets are dirty. It would be great if you could toss them and just buy a new set but they don't sell them. Anywhere. I would contact Z1Enterprises.com and buy and inexpensive jet cleaning tool. It essentially is a bunch of light gauge wires with some of the thicker having rough edges. You won't use the thicker ones...

I hate to tell someone to use one of these tools since they are basically destructive in nature; you will be scraping the small hole inside the pilot jet so please take it easy. If you start to see any brass flakes you are WAY too vigorous with the thing.

Next, turn your pilot mixture screws to 2 turns out and give it a shot. If you continue to have problems, you may have internal obstructions that are blocking internal passageways.

Thanks for all the tips. On a whim, I turned out the pilot screw to 4 turns out, and the bike started better, but didn't run as good at 1/8 throttle, there seemed to be a little dead spot.

I am confused because my Clymer manual calls the pilot screw a pilot air screw and says that as you turn it out, you lean the mixture. I am assuming this is a mistake in the Clymer book.

When I get the pilot cleaning tool, I am going to give the pilots a good cleaning.

Also when it warms up here above 50 degrees, the bike may run better.

I know on the Mikunis that air screw cuts air as you screw it in more thereby enrichening the mixture. Maybe the manual is referring to a Mikuni?

Probably. The last chapter in the book is an update for '82 and newer, and they have the Mikunis.

I removed the carbs again, cleaned them thoroughly. Took each jet and used the jet cleaning tool and made sure all passages were clear. Shot air through all the passages on the carburetor. Installed carb kit parts (new orings, float needle, pilot screws, etc.). Set pilot screws to 2 turns out from seated. Still doesn't start good, and runs poorly at idle to 1/4 throttle. When warmed up it runs erratic. Good for a while, then rough. Any other ideas? I noticed yesterday some oil seeping from the head gasket. Could this be an issue? Plugs have good spark, still not sure if I have a vacuum leak somewhere. Doesn't appear to be leaking at the carb boots. Any other areas to check? Thanks.