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Kz 650 is starving.

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21 Apr 2006 20:59 #41577 by fuzzwardo
Kz 650 is starving. was created by fuzzwardo
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.

1978 Kz650B
2001 ZX9R
1996 zx9r project
1985 Suzuki SP250
1991 Harley Electra-glide classic

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22 Apr 2006 06:10 #41623 by captaincrusty51
Replied by captaincrusty51 on topic Kz 650 is starving.
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

1978 KZ650C
Keihin CR Special carbs, MAC 4 into 1, Koni Shocks, Emgo Pods


2002 ZRX1200R
Akrapovic exhaust, Teds Ignition Advance, Steering Damper, Dunlop Qualifier tires, Corbin GF/L,Rear tire hugger, Tsukigi braces

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22 Apr 2006 08:17 #41639 by OKC_Kent
Replied by OKC_Kent on topic Kz 650 is starving.
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.

Oklahoma City, OK
78 KZ650 B2 82,000+ miles

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22 Apr 2006 10:41 #41651 by reborn650
Replied by reborn650 on topic Kz 650 is starving.
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

-1977 Kz650 Custom bought new by brother. Now with 810 kit, GPz750 cams, intake valves, Mikuni 29 smoothbores, velocity stacks, Dyna Igntion, MAC pipe and other goodies.
-1982 Ferrari 308 GTSi Red/Tan
-Toyota FJ Cruiser - 6 speed tank
-2010 Mazda CX-7 Turbo (my bride's)
-1998 Jeep TJ Wrangler 4.0...

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22 Apr 2006 16:18 #41704 by fuzzwardo
Replied by fuzzwardo on topic Kz 650 is starving.
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?

1978 Kz650B
2001 ZX9R
1996 zx9r project
1985 Suzuki SP250
1991 Harley Electra-glide classic

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22 Apr 2006 19:13 #41736 by RetroRiceRocketRider
Replied by RetroRiceRocketRider on topic Kz 650 is starving.
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.

Covina, So Calif!
78 KZ650-B2 = SOLD
84 ZN700 LTD = SOLD
84 ZX750 GPz = SOLD
89 GSX1100F Katana = SLEEPING :-/
20 VN1700 Vulcan Vaquero (the Blue Cowboy)
Looking for my next project KZ

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22 Apr 2006 20:30 #41764 by fuzzwardo
Replied by fuzzwardo on topic Kz 650 is starving.
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?

1978 Kz650B
2001 ZX9R
1996 zx9r project
1985 Suzuki SP250
1991 Harley Electra-glide classic

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23 Apr 2006 11:40 #41862 by wiredgeorge
Replied by wiredgeorge on topic Kz 650 is starving.
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.

wiredgeorge Motorcycle Carburetors
Mico TX
www.wgcarbs.com
Too many bikes to list!

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23 Apr 2006 19:12 #41961 by fuzzwardo
Replied by fuzzwardo on topic Kz 650 is starving.
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.

1978 Kz650B
2001 ZX9R
1996 zx9r project
1985 Suzuki SP250
1991 Harley Electra-glide classic

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24 Apr 2006 06:51 #42112 by wiredgeorge
Replied by wiredgeorge on topic Kz 650 is starving.
I suggest you have a look at my carb connections page on my web site.

wiredgeorge Motorcycle Carburetors
Mico TX
www.wgcarbs.com
Too many bikes to list!

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24 Apr 2006 12:13 #42214 by fuzzwardo
Replied by fuzzwardo on topic Kz 650 is starving.
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.

1978 Kz650B
2001 ZX9R
1996 zx9r project
1985 Suzuki SP250
1991 Harley Electra-glide classic

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24 Apr 2006 13:07 #42233 by wiredgeorge
Replied by wiredgeorge on topic Kz 650 is starving.
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.

wiredgeorge Motorcycle Carburetors
Mico TX
www.wgcarbs.com
Too many bikes to list!

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