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1986 VN750
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3,255 Posts
Discussion Starter #1
After working on my bike for the last few months, I've noticed a loud ticking sound that is most prevalent at idle, but is also intermittent. It really sounded like something in the top-end of a cylinder and I have been somewhat freaking out ever since.

Today I think I narrowed it down to the petcock. It's the original, and has never been rebuilt according to the documentation I have, so I am thinking that is the case. I read a thread about somebody else noting they had a ticking petcock, so that gives me some hope. I couldn't hear the ticking in the cylinder with the screwdriver method, but it is LOUD AND CLEAR on the tank. I even took my carabiner that I keep my keys, tapped on the cylinder heads, and could not get the sound to be that loud in the tank. I also felt the tick a bit when I had my fingers holding the petcock (there is a joke in there somewhere).

So, would a simple petcock rebuild take care of this, do you think? I don't think it's detrimental, but it is annoying. Scared me to death thinking I may have upper chain issues, etc.
 

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1986 VN750
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3,255 Posts
Discussion Starter #2
I just read up on another post with a possible fix from Dave. Quote is below. Here is the post. I'll reply with how it goes. Sorry for posting prior to searching more in-depth.

Fixed! Hallelujah . I ran a T (actually looks like an F) and vac lines to both carbs. My theory was that since only one line was used to supply vacuum the valve was chattering due to the pulse of only the one cylinder pulling. Since both cylinders suck opposite each other, using both on the petcock valve applies more consistent vacuum keeping the valve stable. Worked great! Was so happy I took it for a half hour ride in the rain, ha ha. Hope this helps someone else.
Dave.
 

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That might do it. The sound would be nothing to worry about, let's you know it is working. The diaprahm inside the petcock slides open when there is vacum on every intake stroke on the one cylinder and then closes on the other 3 strokes. Dual vacum would open on 2 strokes, it would actually open and close much more rapidly, but kind of stay open all the time while running cause the spring isn't strong-fast enuff to close.
 

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1986 VN750
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3,255 Posts
Discussion Starter #4
It is nice to know that it is nothing major, but it is somewhat unsettling as it is the only thing I can really hear over the exhaust. With the ACCTs gone, the noise really went down a ton!

I'm going to do this tomorrow in an effort to quieten down the ride. I want to throw in some 42 pilots as I think 40 is too small, and I need to swap the front jet to 142 I think.
 

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1986 VN750
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3,255 Posts
Discussion Starter #5
I just went out and did this mod, and man, it's been the best thing I've done since the ear-shave. It really stabilized my idle, and removed that nasty clanging noise.

I am really surprised. I wonder if the vacuum off one carb doesn't pull enough gas for an ear-shave setup? When I pinched the secondary vacuum, my idle got a little rough again, let off, and it was stable as can be. Either way, hooray! Pics are below...

Left (Petcock) Side


Right (Secondary) Side


It doesn't even look bad, honestly. I just need to take a Sharpie to the T fitting.
 

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10,354 Posts
Nice touch Tanner...Wolfie approves :smiley_th:smiley_th:smiley_th !!!!
And those tees do come in black as well...used in automotive vaccuum applications. Mostly found on 70s-early 80s US cars.
I'd just plugged my other one with a bolt, but dont recall any petcock "rattle"...I am however gonna do this to mine. Just a more professional look as well. Well done Kemosabe....
 

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1986 VN750
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3,255 Posts
Discussion Starter #7
Nice touch Tanner...Wolfie approves :smiley_th:smiley_th:smiley_th !!!!
And those tees do come in black as well...used in automotive vaccuum applications. Mostly found on 70s-early 80s US cars.
I'd just plugged my other one with a bolt, but dont recall any petcock "rattle"...I am however gonna do this to mine. Just a more professional look as well. Well done Kemosabe....
Glad I got the official Wolfie Seal of Approval™ there! I just back from a good hour and half ride (longest since I've done all the engine pulling, stator swapping, etc), and it was a dream! She purrs like a kitten at stop lights, and looks good doing it. :loser1: She ran like a bat out of hell on the freeway. Some have noted a dis-taste for the "drone" of the V&H Cruizers at freeway speed, but I liked it. Maybe I am just happy that the bike is (finally) happy.

I still get some popping in my front exhaust on decel, but I'll work on the pilots, etc, here next weekend or two.

Let us know how your mod goes. :beerchug:
 

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I have had a strange idle issue ever since I got this bike. It is more of an annoyance than a real problem...I may do this just to see if it cures the rough idle issue.
thanks for sharing!
 

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I had the same problem. I never would have guessed it would be the petcock if I didn't read this post. Thanks!

I solved it by putting a restrictor in the vacuum line, close the the front carb. Just a small pieces of plastic with a tiny hole in it.

No need for an extra hose.
 

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2 Posts
stupid question

Hey new to the whole Vulcan world and a bit of a newbie when it comes to the cruiser stuff but i have a 85 VN 700 and was wanting to try this mod but i the vac line coming off of my right carb goes to this vac diaphram like thing with two big hoses coming off it what do i need to do about that . thanks for the help
 

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1986 VN750
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3,255 Posts
Discussion Starter #11
Hey new to the whole Vulcan world and a bit of a newbie when it comes to the cruiser stuff but i have a 85 VN 700 and was wanting to try this mod but i the vac line coming off of my right carb goes to this vac diaphram like thing with two big hoses coming off it what do i need to do about that . thanks for the help
That goes to the emissions system, which is removed if you "coaster" the bike. I do suggest doing so, otherwise the poster above mentioned using a restricter to make the vacuum vary less quickly.

If the Vulcan is new to you, have you checked your automatic cam chain tensioners (ACCTs)? They make a clacking noise at the top end of each cylinder. A lot of people replace them with manual tensioners, such as myself. TOC makes some premade ones that are nice, some modify their ACCTs to MCCTs, but that's not my preferred path.
 

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...bad ACCTs also cause noise lower, not just at the top, from "chain slap"...
 

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Thanks for the info. i will def. check the cam chain tensioners also i was wondering if any of you had a link or could tell me how to "coaster" my bike i searched it in the forums search and couldnt come up with any thing again thanks for all the help
 

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Linkmeister Supreme
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7,960 Posts
Thanks for the info. i will def. check the cam chain tensioners also i was wondering if any of you had a link or could tell me how to "coaster" my bike i searched it in the forums search and couldnt come up with any thing again thanks for all the help
A "coaster" is just a metal plate to replace the reed valves that feed air into the exhaust manifold.
Link to vulcan verses:
http://www.vn750.com/forum/showthread.php?t=1085

picture of a coaster in this thread:
http://www.vn750.com/forum/showthread.php?t=18726&highlight=coasters
 
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