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1994 XV750 Pressure sensor? AIS [SOLVED]

Have a question about fixing something on a Yamaha Virago XV750? Post it here!

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Mozzer
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1994 XV750 Pressure sensor? AIS [SOLVED]

Post by Mozzer » Mon Oct 07, 2019 5:20 pm

Hello all,
Does the 1994 XV750 have a pressure sensor ? could I connect the line straight to the petcock to the carb boot If I wanted to remove the AIS? I realize there is lots of info on this but Im having trouble for finding info for my model
Thanks
1994 XS750

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ViragoJoe
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Re: 1994 XV750 Pressure sensor? AIS

Post by ViragoJoe » Tue Oct 08, 2019 10:35 am

Mozzer wrote:
Mon Oct 07, 2019 5:20 pm
Hello all,
Does the 1994 XV750 have a pressure sensor? could I connect the line straight to the petcock to the carb boot If I wanted to remove the AIS? I realize there is lots of info on this but Im having trouble for finding info for my model
Thanks
Hello mozzer,

No Pressure Sensor on XV750's.

“Pressure Sensor”

"With the introduction of the XV 1000 in 1984 a box called the Pressure Sensor was added, and is found on all 1000, and 1100 models.. This sits in front of your engine near the coils. It has a vacuum input from one of the carbholders and several wires going to the TCI. My understanding of its function is this: when the throttle is closed and the bike goes into deceleration, the increased vacuum activates a switch in the sensor which sends a signal to the TCI to retard the ignition timing–a smog thing. These never seem to be an issue one way or the other, and I always leave them hooked up."


AIS Pipes

"Starting in 1984 (in the States at least) Yamaha added something call the Air Induction System (AIS) to their larger model Viragos. This system was designed to decrease emissions by injection air at the exhaust valve outlet when the bike was decelerating in order to promote more complete burning of the fuel mixture and thus cleaner exhaust gasses.

The way it works is that when the throttle is closed on deceleration, a relatively high vacuum condition is created in the intake path between the carb and the intake valve. This vacuum is sent from a vacuum port in the front carbholder to a valve which sits in the left hand pod. The valve then opens, allowing air to be sucked into the exhaust gas path just after the valve.

Is there a problem here? Not really, and you can leave the AIS system alone. I see no reason to remove it, particularly on Viragos with Mikuni carbs. However, on ealier models with Hitachi carbs, it tends to interfere with access to at least one of the pilot screws.

Also, there is the matter of esthetics. It’s a bunch of pipes messing with the clean lines of your engine, and things look neater without them. Note also, that they don’t affect the running of the bike when you are on the gas, so there is no performance downside if they are gone. Also, their removal should not cause backfiring. Also, for your green folks, let me simply say that trees need CO2 to make oxygen, so direct your exhaust gasses toward trees whenever possible.

Anyway, if you decide to remove these pipes, here’s how. Disconnect the vacuum line at the front carb holder, and cap that port. A ball bearing shoved into a short piece of vacuum hose is one way. Then physically remove the pipes. At the engine you will find some gaskets which adapt the pipe to the stubs coming out of the heads. Leave these gaskets in place. Rush down to your local Ace hardware store and buy a couple of 1/2 inch copper pipe ends. These will fit snugly over those gaskets and cap the stubs quite neatly. Add a little JB weld or other high temp epoxy to hold them on. I’ve never had one come off. A little silver paint and they’ll look like Yamaha OEM equipment."

You asked:
could I connect the line straight to the petcock to the carb boot If I wanted to remove the AIS?
Yes, it needs vacuum to operate correctly.
ViragoJoe
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)

Mozzer
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Re: 1994 XV750 Pressure sensor? AIS [SOLVED]

Post by Mozzer » Thu Oct 10, 2019 7:10 pm

Thanks Joe,
Rear carb ok?
1994 XS750

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ViragoJoe
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Re: 1994 XV750 Pressure sensor? AIS [SOLVED]

Post by ViragoJoe » Fri Oct 11, 2019 7:19 am

Mozzer wrote:
Thu Oct 10, 2019 7:10 pm
Thanks Joe,
Rear carb ok?
Yes, indeed! It just needs a source for vacuum.
ViragoJoe
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)

Mozzer
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Re: 1994 XV750 Pressure sensor? AIS [SOLVED]

Post by Mozzer » Sat Oct 12, 2019 12:22 am

doing it tomorrow,

Thanks so much !
1994 XS750

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