idle problem

i am having similar problems to telefunkin, who posted a thread about idle speed issues. rather than strap a bomb to my chest in a hijack attempt, i figured i would ask my own questions. i have just got my 77 kz650b to start using a couple shots of carb cleaner in the airbox. it is having trouble starting on its own and will start warm but likes the carb cleaner to start cold.

when cold it idles at 2000 rpm till warm. when warm it drops to 1200 or so and dies. could it be my idle adjustment screws?

before i mess with those, i would like to use some carb cleaner to test for leaks. do i just spray it on the boots and carbs with the engine running? what am i looking for? changes in rpm?

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thank you!
-david

Check for leaks first. And you're right, just get it running and spray carb cleaner all around the carb holders. Make sure you spray every side/angle of them so a leak doesn't hide from you. If there's a leak you'll get a drastic change in the idle.

Check that first and if you don't have a leak proceed on to making sure your idle circuit in your carbs is clean.

i will check for leaks later today, but i am beginning to think my petcock might be suspect as well. there is a hose on the back of the petcock that is plugged. i was told it is a vacuum hose.

upon farther inspection i have found:
when switched "res" i get a small drip of fuel every few seconds.
when switched to "pri" one hose gushes fuel.
when switched to "on" the other gushes fuel.
sound normal?

i can get the bike to rev with small twists of the throttle. but if i give it a good nudge the engine dies.

Davestradamus wrote:

i will check for leaks later today, but i am beginning to think my petcock might be suspect as well. there is a hose on the back of the petcock that is plugged. i was told it is a vacuum hose.

upon farther inspection i have found:
when switched "res" i get a small drip of fuel every few seconds.
when switched to "pri" one hose gushes fuel.
when switched to "on" the other gushes fuel.
sound normal?

Sounds like you have a vacuum petcock that has the vacuum feature disabled. It may have some issues, but it is not what is causing your problem.

i can get the bike to rev with small twists of the throttle. but if i give it a good nudge the engine dies.

The problems you are describing sound like blocked pilot jets to me.

Davestradamus wrote:

...petcock might be suspect...hose on the back...is plugged. i was told it is a vacuum hose...
when switched "res" i get a small drip of fuel every few seconds.
when switched to "pri" one hose gushes fuel.
when switched to "on" the other gushes fuel....

A properly functioning vacuum operated petcock requires vacuum to flow any fuel in the ON or RES position. Only PRI position is supposed to flow fuel without vacuum.

The small nipple is for attaching vacuum tube from the carb. Fuel outlet nipples are larger.

Am thinking something's wrong inside the petcock, and that rebuilding it with a kit from Z1E could restore proper function. But perhaps disassembly and good cleaning might rehabilitate it without needing a rebuild kit. Would carefully examine the diaphram, fuel port gasket and o-rings for any visible damage.

Good Luck!

i just started the bike, and did the leak test. it seemed to idle fine. but i had a petcock breakthrough.

i decided to test it when running on all petcock settings. the on and res position died when twisted the throttle hard.
but in prime it started and rev'd fine.

the idle was about 2100 hot which seems high. but it might be ready for a test around the block. any ideas?

i plan on ordering a rebuild kit today to restore proper function to the fuel system.

Hi I have a 78 650b mine idles just fine @950-1050 rpm. check your plugs what do they look like ? Which idle mixture type do you have pilot or air screws? what size pilot jets do you have? makes a big difference in the pilot screw settings

the plugs are new and aren't white nor are they black. They smell fine. I think the petcock should be fixed but it runs pretty well on prime. I have yet to take it out due to insurance and the lack of a proper license plate. I am going to give it a cold start tomorrow and see what happens. Thanks for all your help!

David.

That's idling way too high. Spudbudy's is idling correctly 950 - 1050RPM. I'm thinking you may need to clean the carbs if it won't idle below 2100RPM. Also, check the timing advance to make sure it is lubed and moves freely. Ed

Davestradamus wrote:

the plugs are new and aren't white nor are they black. They smell fine. I think the petcock should be fixed but it runs pretty well on prime. I have yet to take it out due to insurance and the lack of a proper license plate. I am going to give it a cold start tomorrow and see what happens. Thanks for all your help!

David.

While bike is parked, would use whichever petcock position that prevents fuel flow. This is not the PRI position which always allows fuel to flow.

This should avoid possibility of a leaking floatvalve allowing excess fuel into floatbowls which is then supposed to escape from the overflows through tubes routed over the swingarm to underneath the bike.

However, a worse problem can be where there's so much excess fuel getting past the floatvalve into the floatbowl, that it swamps the overflow circuit (for whatever reason), whereby fuel rises up into the carb throat and makes its way into the crankcase.

Good Luck!

shite! i left the fuel switch on last night after giving it a cold start. it didnt start without a little shot of cleaner in the box. (i need to figure out her cold start). it was idling a bit high but responded to throttle just fine.

but of course i left the petcock flowing fuel! i knew better than to do that, i just forgot. i have since written the words cut fuel on a yellow piece of tape to put next to the key. jeez

so there it sat all night flooding away.

now when i start it, it idles about 1000 or less but will not respond to changes in throttle. it dies.

maybe i should air it out for a while.

thoughts? i know, i am an idiot so save those....

it has a cold starting problem because your pilot circuits are partally plugged please remove the carb's clean them properly use spray carb cleaner in all the jets and passages and then blow compressed air through them until you get good air flow through every passage and jet in the carbs and also the bowl's. then amazingly most if not all your carb related problems will majicly disappear. the buy you self a good manually operated pet cock and remeber to shut it of every time you come back from a ride and your fuel system problems will be a thing of the past.