TOPIC:

Hey Guys, I need help. I recently bought a 83' kz750-F1 Shaft, and have replaced the battery, plugs, and cleaned the carbs. I finally got it to start up, however, once it does, it idles extremely high.
The idle adjust knob is all the way out, the mixture screws are at 2 turns out, and the throttle cable is set with a bit of play and it still idles at an extreme rpm. The tach is broken, so i have no clue what it actually is, but i know it's way too high.
I went through and made sure that nothing was keeping the throttle screws from raising, and the throttle when popped, throws nicely, and returns even better. yet we're still resting at a high idle.
Any ideas?

Thanks in advance.
Dave

1983 Kz750-F1 Shaft

Post edited by: dvbii, at: 2006/12/20 22:53

Post edited by: dvbii, at: 2006/12/20 23:34

Leaky carb manifold(s)maybe?
Do they look all dried and cracked?

A vacuum line somewhere?

A lean mixture?

How is the fuel-flow from the petcock?

Do You have an inline fuel filter that might be plugging up?

Are You running pods,or the factory airbox?

Choke circuit?Are You turning the choke OFF,once the bike warms up?
How well did You "Clean" the carbs?

I checked all four of the carb manifolds, all look fine.
As far as the vacuum line, the stock has a configuration with #1, and #4 vacuum lines go to a vacuum valve, #3 is capped, and #2 goes to the petcock.
The fuel flows freely to the carbs, all four have full float bowls.
When i say i cleaned, it i mean i took all the rubber out, soaked everything else in carb cleaner, aired it dry, and put it back together.

It is running pods, and as i have never had them on any other bike, it could be the mixture screw setting with those. not sure.

I was starting the bike with full choke, then after a few second, taking it down all the way to off. Still sits at the high idle.

Thanks,
David

1983 Kz750-F1
1983 Kz440-A5
1979 Kz1000-C1

Sandy's question is a good one:

Are You turning the choke OFF,once the bike warms up?

If your carbs have enrichment plungers they can often stay open a bit if dirty or worn, even when the lever is pushed to the closed position. I'll often manually depress each plunger to be sure it can't drop that last bit to a seated position.

Give it a try.
KZCSI

Maybe i am showing my noobie, but i did not see any "plungers". On the Kz1000, yes, but not on the750, it has the diaphram type carbs, and uses a lever system. Is this correct? I checked all of that, and made sure teh the valves were closing correctly.
Thanks,
David

Ok concentrate here. I am guessing that you did turn off the choke right? I had the same prob on my bike, especiall this time I washed it with warm water in the carb holder area. This is my story. When I first got my bike, I took out the carbs to check them , just like you, and when I put them back in it had the high idle prob which was like 4000 rpm. I got a fuel leak around the carb holders, like the fuel left over in the carb would leak out then whatever was outside formed varnish and plugged up whatever on the outside and my high idle slowly went away, however I still had cruise control when I rode it down the road. But yeah, the bike ran a little better and so I washed it one day in the carb holder area and When I started the bike it hit 5000 rpm this time, which pin pointed the area. I went to the store and bought some rtv silicone and ran it through the carb holders and it brought down the idle again. But now I discovered it was one of the hoses on the carb holder that was broken or to say split that was letting in extra air.

Which carbs do you have? Mine are mikini and the none of my tube connections are capped off. As wire George taught me, you have 2 hose connections on no.2 carb one for vacuum and one for a float vent and another on I think carb 3 is another vent nipple which shouldn't be capped off

ok, i have somewhat fixed the idle, turns out it was the throttle cable adjust was caught open. However, no it's either somewhat high idle or stall. there is no in-between. I will check the carb boots again.
But, in reply to the last post, mine are miniki carbs, but each only have a single vacuum connection. carbs 1 and 4 go to a vacuum valve, 2 goes to the petcock, and 3 is capped.
The problem now, as i stated above, is that there is either idle around 3000 or stall out. While adjusting the idle screw i can get it to come down to a point, but then it stalls.
thanks,
david
1983 kz750-f1

The easiest thing to check for is a vacuum leak, which is what it sounds like you're dealing with.

The all time easiest way to check for vacuum leaks is to spray something like carb cleaner, WD-40, etc. at each individual manifold and carb boot with the bike at idle - in your case, the lowest it will idle w/out stalling.
Small cracks and leaks aren't always visible in them.
A very pliable boot or manifold can leak because of a hairline crack, or because one or more of them has warped and leaves a small gap between it/them and the cylinder head.

ok, i will check.
Another question, do i need to adjust he carb mixture screws if there are pods installed? and which way, if so?
The factory setting is 2.0 out.
Thanks,
David

ok, i checked the carb boots, and all seems fine. made sure everything was tight, still idling weird. Can get it pretty low, but not as low as it should without stalling out.
Re-adjusted the mixture screws to approx. 2.25 turns out.
It's getting there. I also imagine that the engine just needs to loosen up some of the crap. i put some seafoam in both the gas and the oil. we'll see.

In view of the work you've already done, I'm guessing the bike did not run or ran poorly when you bought it.

Am wondering about valve clearances and ignition timing (including operation of the advancer unit) which might possibly be preventing a lower idle rpm and should be checked and corrected if necessary before further work on the carbs.

Just a thought.