Throttle Hesitation - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 10 (permalink) Old 11-17-2011, 10:33 AM Thread Starter
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Throttle Hesitation

I have an issue with my bike while cold (not really cold). This issue has gotten gradually worse over the past couple weeks. When it first became noticeable it was only under acceleration for the first second or so of power. I used seafoam in the gas (4.5 oz w/ 3 gal) to see if it might be a carb jet (I don't know **** about carbs) getting gummed up. This seemed to have no effect, neither making the problem better, nor worse.

It is MOST pronounced on the first pull-out of the morning. It actually died in the parking space as soon as I began to roll out (throttle/clutch usage). It has never come close to dying before.

After restarting I revved it a little and then took this video. In the video I roll the throttle around 1/4 and hold it. After getting to speed and stopping again, the bike does not have any issues, even this morning.


http://www.youtube.com/watch?v=1O08TLh1izQ
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post #2 of 10 (permalink) Old 11-17-2011, 11:18 AM
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Sounds like my bike on a very cold morning. Takes a while to warm up.

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post #3 of 10 (permalink) Old 11-17-2011, 11:46 AM Thread Starter
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I didn't really clarify, this is/was after the bike has been idling for 5-10 minutes, I start the bike then go back inside once the idle is stable w/o choke to finish getting ready. I have ridden on mornings MUCH colder than today and it has been nowhere as bad as this morning.

The thing that bothers me is that it has slowly gotten worse, not so much with the weather as it is ALWAYS all over the place in East TN.
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post #4 of 10 (permalink) Old 11-17-2011, 12:14 PM
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I'd do three things.

First drain the gas from the carbs, and fill them with straight SeaFoam, letting it sit over night.

Second I'd check replace the spark plugs.... With iridiums if you have not already.

Lastly I would check the diaphragms in the carbs for tears or tiny holes.

And, I would not let the bike idle 10 minutess to start with... You might just be fouling your plugs.

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post #5 of 10 (permalink) Old 11-17-2011, 01:09 PM Thread Starter
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Quote:
Originally Posted by Knifemaker
I'd do three things.

First drain the gas from the carbs, and fill them with straight SeaFoam, letting it sit over night.
I will do this tonight, I have both spray (aerosol) and liquid, but I am thinking the easiest way to go about it would be to spray into the line between petcock and carb, correct?

Quote:
Originally Posted by Knifemaker
Second I'd check replace the spark plugs.... With iridiums if you have not already.
I replaced them w/ NGK Iridiums a little over 1000 miles ago, the problem began only in the last few hundred miles. I pulled and checked them anyway, they have *slight* carbon buildup around the base (on the threads) below the electrodes, but the electrodes appear to be fine (color/wear/residue) otherwise.

Quote:
Originally Posted by Knifemaker

Lastly I would check the diaphragms in the carbs for tears or tiny holes.
If i am going to go to the trouble of disassembling the carbs, should I just go ahead and track down the parts for a rebuild? After I try seafoam in the carbs directly, I mean.

Quote:
Originally Posted by knifemaker
And, I would not let the bike idle 10 minutess to start with... You might just be fouling your plugs.
I was not aware this could cause an issue and have been letting it warm up "extra long for good measure." I will stop this immediately.
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post #6 of 10 (permalink) Old 11-17-2011, 01:17 PM
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I would only add that it might not hurt to check/clean/lube the air filters if not done in a while.

Also, for running 5~10 minutes in above freezing temps, your temp guage hadn't even moved off the left stop. Maybe the thermostat is also not closing properly?

Good hunting,

~~C8>
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post #7 of 10 (permalink) Old 11-17-2011, 01:59 PM
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Does seem like a carb problem to me... I had a similar problem which went away by taking off the carbs and giving a thorough cleaning with carb cleaner. Disassemble, use carb cleaner only on metal parts, reassemble (making sure everything seals properly, especially the diaphragms). Also should make sure the carb boots are sealing right when you put them back on.
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post #8 of 10 (permalink) Old 11-17-2011, 03:08 PM Thread Starter
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Quote:
Originally Posted by ZCraggRatt View Post
I would only add that it might not hurt to check/clean/lube the air filters if not done in a while.

Also, for running 5~10 minutes in above freezing temps, your temp guage hadn't even moved off the left stop. Maybe the thermostat is also not closing properly?

Good hunting,

~~C8>

I checked the air filters when I changed the plugs a little over 1,000 miles ago, but will check them again to be sure.

The bike had actually been running for about 15 minutes and had been ridden almost out of the apartment complex at the time I took the video. The temp was 40F and I didn't have this problem the 2 days I rode in 30-32F weather a few weeks ago.


Ceal - I will try to seafoam them before I jump into messing with the carbs, but I am not against a complete teardown and rebuild. I will likely try that next if the seafoam does not help.

Last edited by DevinWolfe; 11-17-2011 at 03:10 PM.
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post #9 of 10 (permalink) Old 11-18-2011, 01:48 AM
Crap, I WAS in 5th gear.
 
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Remove your idle mix screws (don't lose any parts!) and spray carb cleaner in the holes. Make sure the needles are clean. If none of this helps and there are no air leaks anywhere, your pilot circuit will probably need to be cleaned by taking the carbs apart. Before doing any carb work, be sure to check the float levels.
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post #10 of 10 (permalink) Old 11-19-2011, 03:18 PM
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"And, I would not let the bike idle 10 minutess to start with... You might just be fouling your plugs." This one I have to disagree with. It will not foul the plugs unless you leave the choke on too long. I have been doing this for 150,000 miles on Vulcan 750s, and never had problems with the plugs. I let it run on the stand until the needle on the temp gauge reaches that second mark from the far left, but I turn the choke off as soon as it will idle without it. Once the needle has reached that mark, it should respond normally to throttle. If not, it is most likely due to dirty carbs. You can try soaking them in Seafoam on the bike first, if that doesn't work, it's time to pull the carbs, take them apart, and give them a thorough cleaning. I would NOT use keytone based automotive carb cleaner in motorcycle carbs, except to clean them after they have been disassembled and all rubber and plastic parts have been removed. It can damage these parts.

I am a motorcyclist, NOT a biker.


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