SLOW return to idle - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 41 (permalink) Old 10-14-2013, 03:58 PM Thread Starter
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SLOW return to idle

I just finished cleaning the jets (done without removing the carbs) and it ran fine. Everything worked as it should. I rode it for a couple hundred miles, no problems. Then after letting it sit for a couple of days, I started it up, with the choke on, turned the choke off, and it settled into a perfect idle. I blipped the throttle a couple of times, and it dropped down to about 3000 rpm, and stayed there for at least 15 seconds, then slowly dropped back down to 1200 rpm. The throttle assembly, cable, and spring have been ruled out. I made sure the tang where the throttle cable connects was fully closed against the stop. Idle was still high. Then it slowly dropped to normal. It has never done this before. Any ideas?

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #2 of 41 (permalink) Old 10-14-2013, 05:47 PM
..have a vulcan good day!
 
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Check your carb boots for leaks, maybe a clamp has become out of place.

Others may disagree, but also I would suspect the Fuel Enricheners :

43028 - 43028-0016 DIAPHRAGM, 5.9MM, AIR CUT VALVE $42.30

...but just cleaning the jets would not have caused those to go bad suddenly.

'86 VN750 13,700 mi -Stock
-Purchased 2008 w/8800mi
Replaced ALL Cables . Kuryakyn LED Voltmeter
SilverStar Ultra 9003/HB2 H4 Headlamp, Jardine Fwd Controls,
Iridiums DPR7EIX-9 & Wires, Tuxedo Mod, Coil Mod, P/U Sensor Mod, Fork Seals,
Splines Lubed - 11/4/2012 - MF AGM Battery
Additional Flashing LED Brake Light on Trunk
Dampers went out @ 13+K !
After TOC MCCT's..... so amazingly quiet I discovered a rattling heat shield on my stock exhaust !
...have a vulcan good day!
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post #3 of 41 (permalink) Old 10-14-2013, 06:13 PM Thread Starter
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Thanks for the information. Whatever it is, it in inside the carbs. I made sure the throttle closed all the way (at the carbs), and that the starting enrichener plungers also closed all the way. And I pulled the elbows off the carbs to make sure the vacuum slides were not sticking. There is no smoke or gas smell, so it does not appear to be running rich while it is idling too fast. Something involving vacuum would make sense, mechanical parts do not move slowly like that. I checked for vacuum leaks between the carbs and heads and didn't find anything. It behaves just like you were holding the throttle open at 3000 rpm or so, then slowly released it, yet it is completely closed.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #4 of 41 (permalink) Old 10-14-2013, 06:23 PM
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Quote:
Originally Posted by VN750Rider/Jerry View Post
Thanks for the information. Whatever it is, it in inside the carbs. I made sure the throttle closed all the way (at the carbs), and that the starting enrichener plungers also closed all the way. And I pulled the elbows off the carbs to make sure the vacuum slides were not sticking. There is no smoke or gas smell, so it does not appear to be running rich while it is idling too fast. Something involving vacuum would make sense, mechanical parts do not move slowly like that. I checked for vacuum leaks between the carbs and heads and didn't find anything. It behaves just like you were holding the throttle open at 3000 rpm or so, then slowly released it, yet it is completely closed.
Yeah, that was my issue...idle @ 3K, sometimes the rpm came down, but not always.
Also would not idle cold.
Problems went away by repositioning / tightening Boot Clamps (vacuum leaks).

Possible leak (pinhole/crack) in the boots ?

hope this helps

'86 VN750 13,700 mi -Stock
-Purchased 2008 w/8800mi
Replaced ALL Cables . Kuryakyn LED Voltmeter
SilverStar Ultra 9003/HB2 H4 Headlamp, Jardine Fwd Controls,
Iridiums DPR7EIX-9 & Wires, Tuxedo Mod, Coil Mod, P/U Sensor Mod, Fork Seals,
Splines Lubed - 11/4/2012 - MF AGM Battery
Additional Flashing LED Brake Light on Trunk
Dampers went out @ 13+K !
After TOC MCCT's..... so amazingly quiet I discovered a rattling heat shield on my stock exhaust !
...have a vulcan good day!

Last edited by WilliamTech; 10-14-2013 at 06:27 PM.
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post #5 of 41 (permalink) Old 10-14-2013, 06:56 PM Thread Starter
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You were right about that enrichener thing. It was the enrichener diaphragm on the front carb. I took the rear one apart, and everything was fine as far as I could tell. Then I removed the front one, and it was all sticky and melted. Both the diaphragm and the little 0-ring. Looks like damage caused by ethanol. I found the diaphragm in my petcock in the same condition a couple of times. I got black stuff all over my fingers just from touching it. There was melted rubber on the carb and the diaphragm cover. It was really gooey. It was almost certainly sticking. I sprayed it good with carb cleaner, and black stuff went everywhere. Then I soaked it in WD-40 and looked it over really good. It wasn't sticky anymore, and I couldn't find any holes in it, so I put everything back together, and it now returns to idle just fine. I'll order a new one. Glad to have found the problem before I needlessly removed the carbs.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #6 of 41 (permalink) Old 10-14-2013, 08:16 PM
..have a vulcan good day!
 
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43028 - 43028-0016 DIAPHRAGM, 5.9MM, AIR CUT VALVE $42.30

I have also seen/found these @ $38.00, and one online link @ $28.00+/- ....

I'll try to locate that link for you.


'86 VN750 13,700 mi -Stock
-Purchased 2008 w/8800mi
Replaced ALL Cables . Kuryakyn LED Voltmeter
SilverStar Ultra 9003/HB2 H4 Headlamp, Jardine Fwd Controls,
Iridiums DPR7EIX-9 & Wires, Tuxedo Mod, Coil Mod, P/U Sensor Mod, Fork Seals,
Splines Lubed - 11/4/2012 - MF AGM Battery
Additional Flashing LED Brake Light on Trunk
Dampers went out @ 13+K !
After TOC MCCT's..... so amazingly quiet I discovered a rattling heat shield on my stock exhaust !
...have a vulcan good day!
WilliamTech is offline  
post #7 of 41 (permalink) Old 10-14-2013, 08:38 PM
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post #8 of 41 (permalink) Old 10-15-2013, 10:45 AM
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I have had the same sympton on occasion and a good dose of seafoam fixes it...no need to take apart the carbs for 7 years and counting.

There really is no better cure to these sort of issues than preventative maintenance. Regular use of seafoam on every third tankfull prevents such issues, but a heavy dose of seafoam usually helps clean out the entire fuel system.
I also use it in the oil and put about 200 miles on it before every oil change.
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post #9 of 41 (permalink) Old 10-15-2013, 02:43 PM Thread Starter
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I definitely agree with using Seafoam, I use it in all 5 of my bikes, at least as much as I can afford. It works wonders for removing old gas residue. But there is a new issue out there now. Ethanol gas. It melts rubber, rusts steel, and corrodes aluminum and brass. Since ethanol is heavier than gas, if left to sit, it will find it's way to the bottom of the tank, or the float bowls, and in the case of the VN750, that little place on the bottom of the carbs where the jets are. The gas will evaporate, leaving the usual deposits, but the ethanol stays longer, and will start corrosion on the surface of the float bowls. Like rust, once corrosion starts, it doesn't stop. I have taken apart carbs that were so badly corroded that the float bowls had to be replaced. Found an old Goldwing with all 4 carbs in that condition. You can get fuel stabilizer designed for use with ethanol, I have never used it, but have been told it does not work well.

As for the damaged diaphragm on my carb, I have no idea how fuel even got to it. It is something that should not require maintenance. I find it odd that the rear one was perfect after 12 years, but the front one was badly damaged. Neither cover had ever been off.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
VN750Rider/Jerry is offline  
post #10 of 41 (permalink) Old 10-16-2013, 01:57 PM
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so what is 'normal' idle on a 1986 750 vulcan? I was wondering since I rebuilt mine if it was idling correctly, it sounds ok but your thread made me wonder what was normal operating speed for idle? (sorry if I am highjacking your thread)

BeeSea
1986 750 Vulcan
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from the case up.(And it runs)
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