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ViragoTechForum.com Tech Articles MCV/AIS removal

#1:  MCV/AIS removal Author: draper84 Post Posted: Sat Mar 22, 2008 3:10 am

This post is meant to be a step by step on how to remove the mcv/ais on the 1985 xv1000. i hope to write it so everyone can understand

1. Remove the bolt under the left side bug eye (shiny silver thing where your left knee would be if you were riding the bike)

2. remove the silver cover by pulling out and up.

3. remove the hex bolts holding the mcv/ais plate on the motorcycle. (one on the top right and one on the top left)

4. At this time you will be able to access the clamps and vacuum lines that go into the mcv/ais unit. begin to remove those clamps.

5. take all of the vacuum lines off of the mcv/ais unit. at this time it should look similar to this [img=left]<a href="http://s86.photobucket.com/albums/k94/Eelwallet/?action=view&current=015.jpg" target="_blank"><img src="http://i86.photobucket.com/albums/k94/Eelwallet/015.jpg" border="0" alt="Photobucket"></a>[/img]

6. take the small vacuum hose coming from the front of the bike apart from the "T" this small hose goes to the pressure sensor that controls the timing of the motorcycle. [img=left]<a href="http://s86.photobucket.com/albums/k94/Eelwallet/?action=view&current=014.jpg" target="_blank"><img src="http://i86.photobucket.com/albums/k94/Eelwallet/014.jpg" border="0" alt="Photobucket"></a>[/img]

7. at this time we can take the vacuum hoses off of the carburetors remove the two hoses that attach to the front carb boot and plug the larger connection with a vacuum plug. (1) [img=left]<a href="http://s86.photobucket.com/albums/k94/Eelwallet/?action=view&current=018.jpg" target="_blank"><img src="http://i86.photobucket.com/albums/k94/Eelwallet/018.jpg" border="0" alt="Photobucket"></a>[/img]
(2) [img=left]<a href="http://s86.photobucket.com/albums/k94/Eelwallet/?action=view&current=019.jpg" target="_blank"><img src="http://i86.photobucket.com/albums/k94/Eelwallet/019.jpg" border="0" alt="Photobucket"></a>[/img]

8. Now remove the coil cover under the forks of the motorcycle and you can see where the small vacuum hose runs. i re-routed this through the opposite side (Left if you are looking at it from the front of the bike) to gain a little more length.

9. plug the small vacuum hose onto the small connection on the front carb boot. this will let you still have timing on your bike. kind of important

10. next we can remove the clamps that hold the 1/2" chrome lines to the engine. these after the clamps are loosened should come right off. [img]<a href="http://s86.photobucket.com/albums/k94/Eelwallet/?action=view&current=022a.jpg" target="_blank"><img src="http://i86.photobucket.com/albums/k94/Eelwallet/022a.jpg" border="0" alt="Photobucket"></a>[/img]

11. now for the fun part. to cap these connections. i used a smooth rivet type of thing that was a snug fit into the port, tapped it in with a rubber mallet and put a hose clamp back on ( also have read of people just connecting these lines with the black hose between them)

12. checklist.
a. (most important) small vacuum hose from pressure sensor connected to small connection on front carb boot
b. large vacuum port on front carb boot plugged
c. two 1/2" exhaust ports plugged or connected
d. unused vacuum lines removed from between carbs
e. backfire gone Laughing Laughing

#2:   Author: draper84 Post Posted: Sat Mar 22, 2008 5:42 am

i just did this, a new clutch, seafoam treatment, some wiring, fuel filter, new plugs (autolite ap63), now my bike is like a whole new bike and woah it's fast

#3:   Author: sdswingr Post Posted: Wed Apr 02, 2008 9:49 pm

question, the two wires coming from the AIS system. What did you do with those? Just clip them?

#4:   Author: sdswingr Post Posted: Wed Apr 02, 2008 10:04 pm

ok, one more..there are two hoses coming out of the rear of each carb. the one from the left carb goes directly to the ais, the one from the right looks like it goes to the air filter pod, either that or it comes from the left side and crosses over to the right...? Do I plug these, or keep them free flowing?

#5:   Author: draper84 Post Posted: Thu Apr 03, 2008 3:32 pm

are these hoses large or small if they are large you have to keep them and i think they terminate in an area the does not get much turbulent air, if they are little then i would plug them, as far as the wires go, my ais did not have wires, so i'm not sure what to tell you, they might have changed this between the 1000 and the 1100 models. maybe if i had some pics i could better tell you

#6:  Re: MCV/AIS removal Author: tagedieb Post Posted: Wed Sep 17, 2008 8:20 pm

great instructions. at steps 10-11 I did it a little differently. I completely removed the metal elbow joining the 1/2" chrome lines to the cylinder head. I removed the 1/2" lines also.

Then I plugged the hole in the cylinder head with a 12 mm aluminum plug. 12 mm was a little tight. A hair smaller would have fit better.

#7:  Re: MCV/AIS removal Author: toohightodie Post Posted: Tue Jan 06, 2009 1:43 am

When you perform the AIS removal, do you removal all the vac lines from the rear carb manifold and leave them open?

#8:  Re: MCV/AIS removal Author: scootermcq Post Posted: Tue Jan 06, 2009 7:22 am

You need to cap the line running to the rear carb, or you will suck air. I plugged mine with a tire patch plug and rubber cement, so now I have a 1" solid rubber plug on the carb manifolds.

Some people use golf tees or the like to plug the hole.

#9:   Author: club_c Post Posted: Tue Jan 06, 2009 1:02 pm

Vacuum caps from your fav auto parts store. Use little clamps too in case you backfire, which will push them off.

#10:  Re: MCV/AIS removal Author: godrocksus1 Post Posted: Fri Jul 10, 2009 9:17 pm

This is a great thread but the pics don't work for me. Anyone have these pics they can email? godrocksus1@gmail.com

#11:  Re: MCV/AIS removal Author: grazingazer Post Posted: Sat Jul 11, 2009 8:08 am

if you change

[img]<a href="http://s86.photobucket.com/albums/k94/Eelwallet/?action=view&current=015.jpg" target="_blank"><img src="

to read:

http://s86.photobucket.com/albums/k94/Eelwallet/?action=view&current=015.jpg

the info you seek is #5 at the bottom of the page after you click on albums at the top of the page...but you need to do the leg work

#12:   Author: evolution9 Post Posted: Mon Sep 07, 2009 12:07 pm

so does anyone have pics that work.what do i do with the vaccum line thats coming from the fuel petcock..do i cap it or do i connect it to the intake boot for the front cyclinder.;

#13:   Author: evolution9 Post Posted: Mon Sep 07, 2009 12:13 pm

i have a 96 xv750

#14:  Re: MCV/AIS removal Author: carl Post Posted: Mon Sep 07, 2009 12:23 pm

You should have only one vacuum line from the carb boot going to the petcock after the MCV is removed. No open vacuum lines.

You might want to check that petcock for leaks when your done with the MCV removal.

#15:   Author: evolution9 Post Posted: Mon Sep 07, 2009 6:48 pm

no leaks there..see the problem im having is when i ride the bike normal its fine but as soon as i put a load on it like merging on a free way it starts to missfire..and its only when i get in the range of 4-5k rpms..i read somewhere that it might be the plugs so im gona try that this afternoon and report back..

#16:   Author: fire831rescue Post Posted: Mon Sep 07, 2009 7:11 pm

I notice this was posted for the 1100. Can it be done on a 1992 XV750?

#17:   Author: scootermcq Post Posted: Mon Sep 07, 2009 7:39 pm

Can & should

#18:   Author: fire831rescue Post Posted: Mon Sep 07, 2009 7:50 pm

The reason I ask is the front pipe for this box has actually broken off on my bike and I wanted to know if I could remove this off my bike without any harsh effects. What is the purpose of this box to begin with? To me it seems like some type of EGR system, like you would find on a car. If I can remove it, then that would be one less problem to fix. I would leave the pod there, just unhook the box.

#19:   Author: evolution9 Post Posted: Mon Sep 07, 2009 10:51 pm

so i swapped plugs still got the same problem..can running without the slip on portion of the exhaust cause a missfire at high rpm..i had to remove it cause it was rusted through and i havent made a replacement can this be the cause?the bike is just running off of headpipes untill i can get some custom pipes done..

#20:  Re: MCV/AIS removal Author: camos Post Posted: Tue Sep 08, 2009 2:43 am

@fire831rescue:
From what I have been able to acertain the MCV/AIS systems work as intended on properly running stock engines. These systems add air on decel to burne extra fuel to prevent popping and backfires in the exhaust. Since most 20+ year old Viragos are neither stock nor properly running, removing them is usually a good thing to do. I think mostly the AIS/MCV are a source of vacuum leaks that can be a headache even on stock properly running engines.

@evolution9:
Running without the mufflers creates more air flow creating a lean fuel mix which can result in misfires and popping. The air filtre and exhaust both affect the amount of air supplied for combustion. Changing either requires adjustments to maintain a proper air fuel mixture.

Cheers
Clive

#21:   Author: kinzo_2004 Post Posted: Tue Sep 08, 2009 3:19 am

Should I do this on a '95 1100 Virago? I could use the space there for other things.

#22:   Author: evolution9 Post Posted: Tue Sep 08, 2009 11:38 pm

camos wrote (View Post):
@evolution9:
Running without the mufflers creates more air flow creating a lean fuel mix which can result in misfires and popping. The air filtre and exhaust both affect the amount of air supplied for combustion. Changing either requires adjustments to maintain a proper air fuel mixture.

Cheers
Clive


so once i get all mystuff put back on it should run like it did before i started chopping it..ill start on that this weekend and report back.thanks for the help camos

#23:   Author: uscgbyron Post Posted: Mon Jan 18, 2010 4:35 pm

I just followed this procedure on my bike, but I have a question. I have a small vacuum connection on my front carb boot but there is also one on the rear carb boot. There is no mention as to what to do with the rear connection. I reconnected the line from the front of the bike to the front carb boot and capped off the connection on the rear boot. Did I do this right? I haven't started the bike yet just in case...
Also, I did not see any large vacuum connection on the front boot to plug and am wondering if some bikes do not have that or am I just not seeing it? Thanks.

#24:   Author: funkamongus Post Posted: Mon Jan 18, 2010 4:50 pm

Hmm,m I have a different bie, but have some questions to help you figure it out.. DO you have a real tank or fake one on top? Do you have one, or two petcocks from your tank? gravity fed? On my 920, I have one petcock split to two carbs. My front holder is capped on both because I have no petcock on the other side, if you do, take one line to it. and my rear holder has a line from the petcock, for the gravity fed system. Just make sure the petcock/petcocks have their hose, but no hoses to the AIS or MCV.

#25:   Author: uscgbyron Post Posted: Mon Jan 18, 2010 5:22 pm

I have an upper and a lower (reserve) tank. The lower tank is under the seat on the left. It is gravity fed from the main tank and then a fuel pump draws from there to feed the carbs. No petcocks at all.

What worries me most is that connection on the rear carb. In the instructions it says that connection on the front effects timing and I wonder if that rear connection has an effect on timing as well.

#26:   Author: funkamongus Post Posted: Mon Jan 18, 2010 5:36 pm

oh... hmmm.. couldnt say,, have to let someone else weigh in on this one.. sorry!!

#27:   Author: uscgbyron Post Posted: Mon Jan 18, 2010 6:23 pm

Ok, thanks for chipping in.

#28:   Author: grazingazer Post Posted: Tue Jan 19, 2010 11:31 am

uscgbyron wrote (View Post):
I have an upper and a lower (reserve) tank. The lower tank is under the seat on the left. It is gravity fed from the main tank and then a fuel pump draws from there to feed the carbs. No petcocks at all.

What worries me most is that connection on the rear carb. In the instructions it says that connection on the front effects timing and I wonder if that rear connection has an effect on timing as well.
the manifold pressure sensor is what affects the timing...it must have a vacuum line hooked to it and to a manifold vacuum source it doesn't matter where the source is so long as it is manifold vacuum that is being supplied

#29:  Re: MCV/AIS removal Author: uscgbyron Post Posted: Tue Jan 19, 2010 2:08 pm

GG, thank you. That makes me feel a lot better. I'll start her up when I get home this evening and see how it goes.

#30:  Re: MCV/AIS removal Author: ryanxv1000 Post Posted: Fri May 21, 2010 1:13 am

i just talked to this guy who swears up and down he has been working on virago's for 20 years, he is saying they need the ais system on the xv1000's to run right and get full power... i took mine off but havent fired it up yet(at all),,, should i reinstall it and get it running and tuned and then remove it or just keep going without it? thanks

#31:   Author: Matthew Post Posted: Fri May 21, 2010 2:37 am

maybe hes confusing the AIS with the pressure sensor for the TCI some had.

And yes, without that, the TCI don't advance timing right.
ViragoTechForum.com Tech Articles MCV/AIS removal


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