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post #1 of 5 (permalink) Old 07-01-2012, 10:45 PM Thread Starter
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Carb air hoses

I think this is the best place for this topic...
Just got my vulcan 750 1990. It runs, but if left idling the RPMs will slowly get slower and slower until it kills it self. The air hoses under the tank that go from the black plastic box to the carbs are not sealed to the black plastic box that the air filter is connected to. (Not sure on the technical term). Both identical hoses that go directly to the carb have been crappily and obviously cut on the top... preventing a good seal. I keep scratching my head as to why someone would do that. There is another tube that goes down in to the bike that was completed off the black plastic box. it was making a suction noise, I have got the small hose back in the right hole. I was wondering if a reason the bike is killing it self could be because of not enough of a vacuum being maintained because of the crappy cut hoses. I plan to replace them no matter what because it looks so stupid, just got to find either a site or dealer. Thanks for any help!

Found a diagram of what hose I'm talking about. It's number 14073A and B.

$50 bucks for rubber?!

Last edited by 1stVulcan; 07-02-2012 at 12:08 AM.
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post #2 of 5 (permalink) Old 07-02-2012, 08:04 PM Thread Starter
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Just Bought a 1990 750, take it home and start tinkering with it, notice that the air duct hoses that connect to the carb aren't going in to the duct flush. Take one off and see that it has been cut, idk why someone would ever do such a dumb thing, but it happened. I also had the other hose that connects to the duct out of it's appropriate hole. I was wondering if these crappy connections would cause the bike to slowly kill it self when left idling. I've got it set for 1k RPM and after about a minute the RPM drops to 400, and eventually will die.
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post #3 of 5 (permalink) Old 07-02-2012, 08:36 PM
..have a vulcan good day!
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It is VERY important to have NO leaks around the carb ducts, for the engine to run at its best w/o issues. Any leaks at the ducts WILL bring on many performance/proper running issues. Each duct is different from the other (front/rear cylinder) and MUST be installed properly....there is a tab on each duct which will indicate proper installment. Any cuts/tears (leaks) in the ducts will give you headache troubleshooting problems beyond belief.
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
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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 #4 of 5 (permalink) Old 07-02-2012, 09:31 PM
Crap, I WAS in 5th gear.
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Generally, an air leak will cause the engine to speed up, moreso when warmed up. Reset your idle mix screws to 2-1/2 turns out as a starting point. You may have some clogging in the carbs with the pilot jets- there's a reason why the boot was cut- the carbs were off before and the yahoo couldn't get the boots aligned.
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post #5 of 5 (permalink) Old 07-02-2012, 11:33 PM Thread Starter
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They are on the right sides but theres no hope of it fitting in the hole, the lip has been completely cut off. I looked up the part, and its $50 for each one... I might be able to find some used ones maybe but i plan to do the ear shave on the bike so I'm not too concerned unless I find more problems from it.
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