Kz 650 is starving.

After letting my '78 warm up for a bit, I'll go for my ride home and it'll start acting like it is starving for fuel and die after a couple of miles. I'll have to then pull off to the side of the road and start it again, it takes the choke to be on to start it. When it does start, it revs to 3000 RPMs or so. It won't idle down. I cleaned the jets and the needles and seats with in the last week. Is it running to lean for some reason? Maybe vapor lock? I just got the bike from my ex brother inlaw and it sat in the storage shed for a couple of years so I'm not real familar with it yet. Any help with this problem would be great.

Couple of thoughts:

Rust or sludge from the tank blocking fuel flow. If its sludge, clean the tank and add a fuel filter inline.

If its a rusty tank, there is lots of info in the archives on tank sealing.

You may have a faulty petcock. They have a vacume line running off one of the carb boots and a leaky line could disrupt fuel flow. Try running off the prime position.

Good luck and let us know if you solve the problem

fuzzwardo wrote:

After letting my '78 warm up for a bit, I'll go for my ride home and it'll start acting like it is starving for fuel and die after a couple of miles. I'll have to then pull off to the side of the road and start it again, it takes the choke to be on to start it. When it does start, it revs to 3000 RPMs or so. It won't idle down. I cleaned the jets and the needles and seats with in the last week. Is it running to lean for some reason? Maybe vapor lock? I just got the bike from my ex brother inlaw and it sat in the storage shed for a couple of years so I'm not real familar with it yet. Any help with this problem would be great.

It might be vapor lock, remove the gas cap and take it apart. The fuel tank vents from the gas cap, clean it up. But really, if it's been sitting for a few years, the carbs need a complete teardown and cleaning. Fuel tank too,like captaincrusty51 said.

Hey Fuzzwardo - I had the same fuel starving?? problem with my 650 last year with Mikuni 24's on the bike.

The inside of my gas tank had been professionally cleaned. I also had a brand new petcock and gas cap from Kawasaki so these parts weren't causing the problem. Sometimes the bike would just begin starving while riding, flipping open the gas cap seemed to temporarily fix the problem but this was a dangerous proposition if the tank was over half full.

I fixed the problem for good by removing the gas cap, taking it apart and using a small drill bit, slightly enlarged the rubber gasket seal (that sat flush against the venting passage) on the underside of the cap. I also very carefully enlarged the venting hole on the metal air passage with a one size larger drill bit. These easy mods allowed for better venting. Take a look at the cap and you will see the curved passage and gasket.

This quick fix should help you with your problem as it worked great for me.

Cheers-Colin Firth -Ontario Canada

'77 Kz 650 Custom - (Miss July on 2006 Kzr Calendar,) Newest rebuild includes Wiseco 810 kit, Kz750 cams, Kz750 intake valves, 750 GPz springs, Ported head, WG Mikuni 28's, Velocity Stacks, Dyna Ignition and coils, MAC pipe, 14 tooth sprocket, going back to original '77 Moon Dust Silver. Goal is to have a stock-looking bike that will tighten up any loose dental fillings off the light.

Post edited by: reborn650, at: 2006/04/22 13:46

I think I found part of the problem. There are 2 hoses, 1 between carbs 1 and 2 and then one between 3 and 4. They are sucking air alot, the left side more than the right. My friend and I plugged them and it runs a lot better. It's not perfect by any means but it isn't dying out anymore. Are these hoses supposed to be plugged into something or capped off?

If the hoses you're refering to are connected to brass fittings protruding from the intake manifolds that are between the carbs and the cylinders, then yes, they should have rubber caps on them.
Those brass fittings are vacuum ports and are used to synchronize the carbs.
If those rubber caps are missing, and rather than spending about $5 each on them at your local Kawi dealership, you can find replacement caps in the HELP brand section of most decently stocked auto parts stores.
They will be listed as vacuum caps. And for reference, I believe the original Kawi caps are 1/8" I.D.

Yes, that is what I am talking about. I'll go and get some caps for them tomorrow. Why would one side be sucking more air than another? Is this going to be a problem in the future?

fuzz... Not really sure what hoses you are referring to... There are short (about 1/2") rubber hoses connecting 1&2 and 3&4 carbs. These are VENT hoses. Each bowl has a vent in its top. the #2 and #4 carbs have brass spigots on the side which are the actual vents. The hoses tie the vent holes in the bowls from 1 to 2 carb and both vent through the #2 vent spigot. Works the same for 3 & 4. There will also be vacuum fittings on ONE carb for assemblies meant to be used with vacuum petcocks. The spigots for the vacuum fittings look the same as the vents. The difference is, the vacuum MUST be plugged or connected and the vents must be open or the floats don't work as they should. See the carb connection guide on my web site for a pic showing locations of vents and vacuum fittings.

I ended up plugging the 2 small brass fittings and the bike is a night and day difference. The fittings are about 1/8"in diameter and 3/4" or so long and the first one is on the second carb from the left side at a 45 degree angle. The other one is on the fourth carb running straight out. When I got the bike, it had yellow see thru tubing on these 2 spots and I never seen where they went to. I plugged the brass fittings and the bike has not acted up on me one bit since and I've put probably 50 miles or so on it. I hope this gives an idea on what I was talking about and doesn't make me sound too dumb.

I suggest you have a look at my carb connections page on my web site.

Looking at you site, they are the vacuum spigots. You had a good pic of what I was talking about with arrows pointing to them and everything. Thanks for the info.

There will only be ONE possible vacuum spigot per carb assembly used for connection to the petcock. Any similar spigots will be VENTS. The vacuum spigots on a CV style carb; either Mikuni or Keihin will be on the carb bodies but on a round slide VM series carb, ONLY ONE vacuum spigot.