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Carburetor Help

Old 01-20-2019, 05:43 PM
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Default Carburetor Help

At least I think it's a carburetor.

Recently acquired a Kawasaki Prairie 360 4x4. It's got a Keihin CVK34 carburetor.

Symptoms are:
Bike starts great, idles smooth, no hesitation on throttle, runs at 5% throttle just as good as it runs at 100% throttle and anywhere in between - no bogging or stuttering.

After riding and coming off throttle, the bike dies when it comes to a stop (CVT, so moving momentum keeps engine rotating until it comes to a stop). After riding and slowing down from speed to a crawl, the bike wants to die, and frequently, it does.

Once bike dies, I have to wait 5-20 seconds before I can get the bike to start. I can run the starter while modulating throttle, or I can just wait the requisite 5-20 seconds. It seems to restart more quickly with the choke on.

If I ride it and come off throttle, but maintain some throttle pressure or blipping to keep the engine running for the aforementioned 5-20 seconds, it regains the ability to idle.

Engine temperature doesn't seem to affect any of the symptoms at all. It's 9 degrees outside right now, and just ripped up and down the driveway before doing donuts in 2wd.

So far, what I've done:

Couldn't get it running at first, replaced the spark plug and it started up, but ran rough. Put some fresh gas in the tank and that helped it run a little better. Tore apart the carburetor and emptied a can of carburetor cleaner into the various jets, holes, needle parts, etc., and reassembled - helped it run a little bit better. Ran it empty and refilled with new gas - helped it run a little bit better. Replaced the intake manifold (rubber boot connecting the carb to the cylinder head) - helped low idle and resolved idle hiccups. Set pilot screw to 1.5 turns as recommended by service manual - affected idle speed but didn't help anything. Played with idle speed adjuster, affected idle speed but didn't help anything.

So far, nothing yet has improved the bike's desire to die after coming off throttle. (It doesn't have any issues coming down from high RPMs in neutral, it's only an issue when it's coming off of a load)

Driveway is concrete approximately half a mile long. I can WOT all the way down, turn around at the end with moderate throttle, and WOT all the way back with no issues, but once I let off the throttle and come to a stop, it dies.

Should I be looking at something else? Coil? Exhaust plugged? Is the pilot plugged? Halp!
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Old 01-20-2019, 06:11 PM
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There should be a pilot jet for the idle, try unscrewing it half a turn and see if that helps. Might just be dying because of a lean idle, just like megSquirt’s dashpot, you need a little extra air/fuel as it returns to idle. So it might be fine idling, but won’t be ok as it returns to idle. Since you’ve already adjusted it, you can try reading the plugs or installing a wideband.
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Old 01-21-2019, 12:40 AM
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I rode a kz440 through my university days and spent 5 or so years living with Keihin CV carbs.
Not sure if there were updates from the 80's to modern day, but here are some rambling memories.

Mine were super touchy about the fuel level in the bowls. Under high vacuum at idle, the fuel level was the most responsive change that I could make. It's pretty easy to check the level with a clear hose connected to the drain valve.
If your float valves are leaking, the fuel level will be off as well.
Curly's recommendation is definitely something to look at as well. I think my idle mixture screws were hidden under pot metal plugs at the very top of the carbs next to the diaphragm covers.
I remember I had issues with those needle valves getting plugged with carbon after a couple of backfires once.
Also my choke had a cam that would bump the throttle plates a little, maybe something else to check.
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Old 01-21-2019, 09:48 AM
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Yeah, I should say that disassembling, cleaning, and reassembly should be your first before any diagnosis. I had 4 of these on my Suzuki, with open exhaust and pod filters. It was re-jetted, but definitely needed non-factory needle settings.
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