1976 KZ 900 Engine Sputters after a mile

Happy New Year to you all.

I've recently pulled the KZ 900 out of the garage after 1 year + of sitting because I was frustrated... and here I am, frustrated again.

I love this bike, and hate it at the same time.

Can you help?

I have purchased rebuild carbs from Wired George. (Super nice) - synced to my bike. I have all new Dyna S ignition (coils and all). I've had the valves checked, etc etc.

Here is what it did today. Started right up... smoked a bit at first (gas is a year old in it) - And then I took it for a spin. The first mile it ran as perfect and smooth as could be. I could hold the throttle at 3k rpm and it was smooth.

Then all of a sudden it acts like its losing power. I can give it more gas and it will take off sputtering like this until I get it pretty wide open and it screams... it backfires, pops and sputters after I let off. It does this forever out and never goes back to running right again.

UNTIL, I let it sit in the 30 degree weather for 30 minutes and then ride it again.. Perfect again and then a short time later, all over again.

I am beginning to think from the backfiring, popping etc, that I have a serious exhaust leak at the engine. A guy that worked on it for me a year ago mentioned that they are leaking and they are tight, so he recommended I change those gaskets out, but never did.

Would this explain it? Possibly?

Other thoughts ?

Chris in Louisville Kentucky
1976 KZ 900
louisvilletemples.com/webposts/kz.jpg

Happy New Year to you too.
First thing I would do is to change out the year old gas and I would do this before running it again. Did you put anything in the gas such as Sea Foam or Stabil before you put it away. While I did that I would make sure the tank is clean and take out the petcock and check the screens. New gas lines and filters and then see what happens. Did you let gas sit in the nice WG carbs for a year too? Might want to drop bowls and see if you have varnish or crud (scientific term). GLuck!

i know this could be way off base and seem idiotic:disclaimer:


my bike would run fine and then once warmed up would lurch and pop and die even.i found i had an allmost tight connection on one coil that would make it sputter and pop and when i slowed down or punched it would act like it was a carb problem and clear out...i could pull over once i figured out what was happening and fix it by moving my tank to the side and pushing the coil connectors back tight into the harness.....then the white wire under the left side cover started slipping out a little sometimes and doing the same popping and stuttering under load..and once i found it and crimped the female a sguig it has not happened any more...same kz900 and year ...good luck

The gas has stabil in it... And yup, the gas sat in the bowls for a year... I took off the carbs and they actually were really clean inside. I cleaned them out just in case. I think I got it cuz it started right up.

I will dump the gas for sure and check everything out. (Screens, etc) - I will also check the coils for being tight also... who knows?

More suggestions while I'm at it?

No comments on the exhaust gaskets?

check the thick short white and red striped wire under the left side cover ..that it is tight ....who knows...good luck

if you had an exhuast leak you'd prob know it it would be ticking.tick ...tick...tickk.....or pssst..pssst...pssstt.. every revolution..at idle you could hear right where its pst.pstp.pst....imo and not the symptoms your having would relate...imo

It sounds like a fuel flow issue.

Check the gas cap - on the underside is a pin-hole vent. This must be clear. You may want to unscrew the gasket retaining plate (three small screws - but cover the gas tank hole first) and clean out the channel.

Check your petcock is flowing fuel effectively.

Remove the fuel hoses from the carbs and have them draining into a container - turn the petcock on and watch and wait. The flow should not slow down. If it does the filter on the petcock is probably covered in crud.

You say it runs great when cold, are you forgetting to put the choke back down once it's warm? I know I forgot once and it ran fine at first but once warmed up a bit the choke was causing a too rich condition.

Also, what Jeff said about the gas cap vent happened to me, cleaned it out and made a huge difference. Vacuum in the tank was preventing the correct amount of fuel from flowing.

Best of luck.

Odd you say that.. I blew a fuse while out today and the wire was hot to the touch.. This is the same white, red striped wire you speak of? Is it possible I didn't have the fuse in tight? What do you mean make sure its tight?

Regarding the vent/gas.. I am going to go out and check that tonight in the garage... never have, who knows?

Also, on the choke left open.. Ya.. I'm sure I turned it off... I double checked it a few times myself

Sounds like crud in the petcock. Drain the tank and clean the screen in the petcock. Sounds like the same thing that happened on a 73 i had awhile back..
cheers

Here's an easy way to determine if fuel starvation is due to improper fuel cap venting.

Just ride with the cap ajar (not clicked down tight), to see whether the starvation continues.

But often (as already suggested), it's grit or crud suspended in the fuel which is hovering around and collecting on the petcock intake screens that protrude up into the tank interior.

Imo it's best to remove tank and flush it by dumping old gas out through the fuel cap hole. Put in a little fresh gas. Swish it around. And dump again.

Would also remove, disassemble and clean the petcock, especially the intake screens that go up inside the tank.

Good Luck!