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post #1 of 12 (permalink) Old 08-13-2011, 04:45 PM Thread Starter
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help, venturi needle bouncing

Hey guys, Im new to here, but need some help
I just bought a 2000 kawasaki vulcan 750, 11000 miles on it, garage kept.
Been battling a running rich problem.
Findings
I have had the carbs apart 3 times and kept thinking i had a jet stopped up or float level problems. I was running way rich on front and back cylinder, way way rich. I got inside the carbs the third time to find that my rear carb float needle seat, was pressed in incorrectly by either keihin or previous owner. I had to re clock it so that the holes were lined up so that fuel could come through them. Before the fuel was being forced up by the needle and preventing the needle to close. I also found that my rear carb air fuel screw was broken, fished out the tiny broken part and replaced
Now i have the air fuel screws set at 1 1/2 turns and I am still a little too rich on the front cylinder.
I also noticed that the venturi needle on the front carb is boucing top to bottom at a rate of about one bounce a second
While assembling i made sure all passages were unclogged and the vaccuum diaphrams had no holes and were properly seated
Now the rear cylinder has cleaned up, no more rich and the front is still puffing black fuel smoke. all of this is taking place at idle to 2500 rpms. then clears up past that.
mods it has is cobra unbaffled exhaust. i have good fire on all plugs, good compression, clean uncontaminated fuel, petcock is operating good.
Cant figure out why the venturi needle is boucing. Do i have so much carbon buildup on the intake valves that it is sucking for a second, is there a leak between the head and carb creating a sucking effect, is it possibly out of time.
any help would be greatly appreciated. I spent 6 years in NASCAR, and 1 1/2 years in nhra as a builder, thought i knew carbs very well, but i am overlooking something that is probably very obviouls, help please
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post #2 of 12 (permalink) Old 08-13-2011, 05:51 PM
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Quote:
I got inside the carbs the third time to find that my rear carb float needle seat, was pressed in incorrectly by either keihin or previous owner. I had to re clock it so that the holes were lined up so that fuel could come through them. Before the fuel was being forced up by the needle and preventing the needle to close.
Welcome to the Vulcan madness jkmfab.

I`m no carb expert but I recall a thread from a member last week about float bowl needles and seats. The seats are an integral part of the carb body and are not replaceable. The shop had to order some sort of special tool to reshape one of the seats on his carb. If that had not worked another carb body would have been needed.

By "reclocking" the seat I believe you mean turning it. I`m not sure how this is possible if the seat is integral with the carb body.

One of our carb gurus will chime in shortly with more info I`m sure.

Gordon

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post #3 of 12 (permalink) Old 08-13-2011, 07:00 PM Thread Starter
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the valve seats are brass seats that are pressed into the body, the body has two notches in it, one towards float bowl cover the other 180 degrees. the jet holes are 1/16th of an inch in diameter. i was not able to remove the seats without doing major damage, so i chocked the body up in my mill, and drilled two new holes where the others should have been. the others are completely blocked by the carb body. I checked my fuel flow the the kaw tool and both of my fuel flow rates are perfect. so thats not why i am running rich. the only thing on this engine that ive yet to check is timing. Im thinking that if timing was one tooth advanced on the front cylinder then it will richen up the cylinder due the valves being opened and closed at the wrong time. You are correct in not being able to safely remove them, thanks for the response
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post #4 of 12 (permalink) Old 08-13-2011, 07:28 PM Thread Starter
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i guess my main question is that i know that the needle operates off of vaccuum, my fuel flow level on my floats are in spec, and the valves are completly closing, if the timeing on the front cylinder has jumped one tooth, then will it cause a disruption in vaccum, and a rich condition. if the intake valves are opening late after spark then it seems like it will cause unburned fuel. on cars, which is my specialty, not bikes, lol, if the timeing is of it lowers the compression due to not getting a full air pressure compression on the compression stroke, any ideas vulcan world.
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post #5 of 12 (permalink) Old 08-14-2011, 06:41 AM
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It may be simpler than timing, etc. I realize you've got a ton of experience, so please don't be insulted by this suggestion, but: is the front carb indicating some back-pressure when you move the slide by hand? Sometimes the diaphragm just does not want to seal up all the way and that will create the needle bounce that you're describing. Check it and re-seat it until you can feel the resistance by hand and then try running the bike again. I've sometimes had to re-seat a slide diaphragm three or four times before it's sitting correctly.

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post #6 of 12 (permalink) Old 08-14-2011, 10:26 AM
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Also the plastic piece that holds the needle down has to be in the right position. It has to be directly touching the top of the needle. If not the needle will move up and down a bit without the slide.

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post #7 of 12 (permalink) Old 08-14-2011, 10:52 PM Thread Starter
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thank you for your response, i am not insulted, i am a bit disappointed in myself for not being able to figure it out on my own. I did check the needle and you are right, the needle had a little room to move up and down before the needle head was contacting the plastic pieced due to the plastic piece being cocked a little to the side. i checked both of them and neither had that much resistance when manually pressed up. I corrected that, checked my timing and my timing is perfect. One thing i have noticed is that my reed valves on the heads are very, very sooted up, im guessin. with them off, i can blow on the nipple end and im getting free airflow, i can suck air towards me on the nipple end and im still getting air flow, just not as free. Isnt that valve supposed to be a one way valve
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post #8 of 12 (permalink) Old 08-14-2011, 11:03 PM
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Yes, it is one way, but the increase in pressure from the exhaust helps seal the valve off.

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post #9 of 12 (permalink) Old 08-14-2011, 11:11 PM Thread Starter
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wow, i am really off of my game, lol. I didnt think about that. Well would the throttle needle be causeing me to still have a slightly rich condition?
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post #10 of 12 (permalink) Old 08-14-2011, 11:15 PM
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Have you adjusted on the air needle on the side of the carbs?

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