Can I cap off the vacuum ports and leave the pairs stuff in place?

[Dale_K]

I found a bad vacuum line on the middle left side cylinder today.  I want to cap off all the vacuum lines except for the one to the petcock.  I would be leaving the air injection smog stuff in place until such time as I actually need to pull the carbs.  Right now the bike runs fine.  I temporarily spliced in a short section of vacuum line and reconnected it.

Does it hurt the bike or make it run poorly if I cap off the vacuum ports (petcock excepted)?  Any danger of creating new problems by leaving the pair/smog stuff in situ?

[Chrisj CMA]

If you don't do the whole desmog and you remove the vacuum lines that run the pair valves, I think you would need to cap the intake nipples and the nipples on each pair valves body

[da prez]

  You do not need to pull the carbs to do a de smog. The right crash bar needs to be removed to make an easy job of removing the air tube. Harbor freight sells a set of long reach ball metric hex keys that are well worth the money to remove the air tube screws. Fuel tank , yes , I haven't found a way around it unless you cut and plug.  Four 14mm freeze plugs is all that is really needed to buy. All else can be done with garage stock. Hook the pet rooster vacuum up to the right rear. Plug all the rest.

                                           da prez
                                                     

[Ken Tarver]

You can leave the chrome tubes and plug them under the tank then ya won't need the freeze plugs.
Follow the easy de-smog method on shoptalk.

Ken

[MarkT]

I cut off at appropriate places, flattened & folded over the pair tubes on Jade & Deerslayer.  Makes the desmog go much easier.  I see no evidence of detrimental behavior.  Vise grips is a good tool for that.

[Fazer]

The hardest part of the job is removing and re-installing the airbox.  If you can cap things off and not have to deal with that, then I say go for it.  But if you need to actually access the pair valve, then going thru with a complete desmog is fairly easy.  Once you cut the chrome pipes, they are easily removed.  I did have to loosen the left side exhaust bank to access the one valve thingy, but it was not that difficult.  With the proper ball end allen wrench (5mm) you may be able to loosen and replace the screws without removing the exhaust, but its hard to get much force on a ball allen wrench to break the screws loose.  The only other thing is to have some 14mm freeze plugs to put in the holes.  I bought mine on ebay, but you may be able to get them at autozone.  9/16" is close to 14mm, but not sure you would be able to find plugs that size.  I coated mine with red RTV and drove them in with a socket that fit the plug on an extension. 

I also took this opportunity to install the dan-mark electric fuel shut off and haven't turned my fuel valve off since I installed it two years ago.

[indybobm]

I asked this same question a couple of years ago, not much response.
After checking the Honda Service Manual page 5-24, the Pair Control Valve takes about 15.7 in of vacuum to shutoff the Pair Control Valve and stop the flow of air to the Reed Valves in the Pair Check Valve Case. No air to the Reed Valves, no air being supplied to the exhaust ports.
So at high vacuum conditions (decelerating down through the gears) the Pair System is shut off.

When the vacuum falls below ~15 inches of vacuum, the Pair Control Valve opens and air from the air box is supplied through the Reed Valves to the exhaust ports.

I think that disconnecting the vacuum lines to intake 2 & 3 (and capping the nipples) would result in the Pair System supplying a constant source of air to the exhaust ports, even when decelerating. Probably not a good idea.

[Dale_K]

Thanks.  That is the kind of info I was looking for.  Basically the answer is no, you can't simply cap off the vacuum ports.

I've ordered some of the miniature hose clamps from Redeye and I'll live with a spliced vacuum line for now.  Also bought the pairs vacuum line repair kit with all new lines but I'm going to postpone that work as long as possible.  I will replace the factory vacuum caps as I can see that one is cracked. 

[Brian]

I used JB Weld to fill the tube ends of the chrome exhaust tubes. Plug the hole in the air box, I used a bolt, washers and a nut using rtv sealer.  Removing the pair valves gives the engine top a cleaner look.