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Discussion Starter #1
I have a 2003 Vulcan with about 2800 miles on it. Been siting for years. Got it running good. Ear shave and coasters done. Ran with no problem for the past week, except the petcock had a small leak. Installed new petcock today. Now it seems to have an oscillating hesitation. Runs good, then boggs for a second, then runs good, and boggs, then runs good, and boggs......

No more leaking though. The petcock is new OEM.
 

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Yes sounds like it's not flowing fuel properly. You can check this by running two fuel lines from the petcock into a jar, and then applying some suction to the vacuum line.
You can use your mouth or one of these:
https://www.walmart.com/ip/Bulb-Syringe-Aspirator/39791322

If the flow seems to swell and then die, you've found your culprit....
 

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I have a 2003 Vulcan with about 2800 miles on it. Been siting for years. Got it running good. Ear shave and coasters done. Ran with no problem for the past week, except the petcock had a small leak. Installed new petcock today. Now it seems to have an oscillating hesitation. Runs good, then boggs for a second, then runs good, and boggs, then runs good, and boggs......

No more leaking though. The petcock is new OEM.
"Got it running WELL."
"Runs WELL, then boggs for a second, then runs WELL, and boggs, then runs WELLER, and boggs......

 

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Discussion Starter #7
Yes sounds like it's not flowing fuel properly. You can check this by running two fuel lines from the petcock into a jar, and then applying some suction to the vacuum line.
You can use your mouth or one of these:
https://www.walmart.com/ip/Bulb-Syringe-Aspirator/39791322

If the flow seems to swell and then die, you've found your culprit....
Thanks! I'll give that a try.


another less likely cause would be inadequate tank venting. may need to clean the vent in the cap and the vent lines
I did clean it last week, but I'll check it again.
 

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Discussion Starter #10
So out of curiosity I took the old petcock apart. Found out that there was no spring in it. So the old one was working like a gravity petcock and worked great (except for the minor leak). Figured I would make the new one gravity fed petcock too. That seemed to fix my problem. The bike is running good now! I took out the plunger in the new petcock and soldered the vacuum nipple shut. I did use a manometer on the carbs and they both seems to have same vacuum on them.
 

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Did you ever connect vacuum from the carbs to the petcock? If so.. wonder why your vacuum is so weak? The stock design has no problem feeding fuel to the bike.

Do you still have all the emissions crap on the bike or did you cap on that second side?
 

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Discussion Starter #12
Did you ever connect vacuum from the carbs to the petcock? If so.. wonder why your vacuum is so weak? The stock design has no problem feeding fuel to the bike.

Do you still have all the emissions crap on the bike or did you cap on that second side?
Yes I did connect the vacuum from the carb to the petcock. All the emmsions stuff is scrapped, ears shaved, and coasters installed. Both carbs have vacuum caps over then. Not sure why the vacuum didn't work on the new petcock. Unless the new one was just old stock sitting around and was stuck. Either way it's going now.

I think it's running good. Seeems smooth. I don't have a real baseline to go off of as it was not running when I got it.
 

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well, glad you figured out what it was needed to make it work right again..

our petcocks are gravity feed (no pump in system). the vacuum port opens the valve completely when vacuum appied. only think I can think of is that the vacuum port on the left carb is plugged in side the carb, that would prevent a good supply of vacuum from getting to the valve.
 

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Discussion Starter #14
PHP:
well, glad you figured out what it was needed to make it work right again..

our petcocks are gravity feed (no pump in system). the vacuum port opens the valve completely when vacuum appied. only thing I can think of is that the vacuum port on the left carb is plugged in side the carb, that would prevent a good supply of vacuum from getting to the valve.
I thought about that too, but I made a home made manometer, and both carbs appear to have the about the same vacuum on them.
 
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