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Discussion Starter #1
Hi all!!

New member here. Been reading around here for awhile but just joined. Lots of good info here!!

Anyway, I have a question that I hope someone can help me out with. I bought a 2002 Vulcan 750 last year. It has about 10k miles on it.

The engine was running rich. I checked the air cut off valves and the plungers were stuck in the bores and the diaphrams were hard and cracked (leaking). I bought a set of air cut off valves (aftermarket brand) and installed them. Initially it ran great. Then, the rear cylinder started running rough (too rich). I pulled the air cut valve back off and found gas in the vacuum side of the diaphram. So, it's gotta be leaking. Maybe I got bad ones? Anyway, I wanted to ride so I blocked off the vacuum to the air cut off valves and it's running great. A little more popping from the exhaust but nothing bad.

I'm getting ready for a week long trip on the bike and will ride about 1000 miles total.

Are there any negative side effects to blocking the air cut valves??




Thanks in advance for any help/advise!!!
 

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1986 VN750
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3,255 Posts
How much play did the metal plunger part have when u inserted it? It should have been somewhat snug with little play.

Does the size look right, etc?

I had mine out recently, and found them to be quite snug to slide in and out (but smooth if you were at a perfect angle)
 

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33 Posts
Discussion Starter #3
How much play did the metal plunger part have when u inserted it? It should have been somewhat snug with little play.

Does the size look right, etc?

I had mine out recently, and found them to be quite snug to slide in and out (but smooth if you were at a perfect angle)


Thanks for the reply!

They looked just like the ones that came out. The new ones were snug but moved freely. The old ones were seized in the bores.

I can't see any pinholes in the diaphram but gas is getting past and into the vacuum port, causing it to run rich...especially at idle.
 

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1986 VN750
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3,255 Posts
Both sides or just one?

If just one, switch them around and see what happens?
 

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Discussion Starter #5
It runs great without them so will it hurt anything to run about 1000 miles without them functioning??
 

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Crap, I WAS in 5th gear.
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500 Posts
It may heat up your exhaust valves. If you're going to do it, screw out your idle bleeds to compensate a little. The biggest effects would be popping in your exhaust, and less engine braking.
 
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