De-Smog .. what’s the benefit

[Deerslayer]

So I hear a lot about guys doing a de-smog mod.
Why is it done ?
What’s the benefit?

Educate me please.

[hubcapsc]

I de-smogged. It de-clutters the motor, that is, it removes the pair
valve and associated tubes and vacuum lines.

I've also helped replace the vacuum lines on an Interstate, it's not hard.

Fixing even small vacuum leaks will make your bike run better.

A desmogged bike might have fewer vacuum lines to go bad, but if you
replace the vacuum lines with vacuum caps, you still have to keep
track of whether or not the caps are leaking.

I doubt I'd desmog again if I got another Valkyrie.

-Mike "minority opinion"

[nogrey]

I’ve de-smogged so many Valks I can’t remember how many.
I’d say the biggest benefit (my opinion) is reliability. De-smogging removes:
Pair Valves
Vacuum control valve
All but one vacuum line
Re-breather port on air box
Re-breather ports on heads (six).
In addition, I always remove the 6 rubber fuel drain hoses (1 attached to each carb).
Also, if you replace your petcock with a Pingle (or similar) manual, you eliminate all vacuum lines.
You still have to cap each of the ports on the downdraft tubes, so those are still a failure item, but seems much easier to me to find a bad one.

The overall appearance of the engine block is so much cleaner and makes maintenance on the carbs less of a hassle (when removing, etc).

Just my opinion. Also, my description of each component may not be textbook.

[Deerslayer]

Is there any difference in how the bike runs?
What’s the job of the pair valve?

Just trying to learn as much as I can about these marvelous machines.

[hubcapsc]

Is there any difference in how the bike runs?
What’s the job of the pair valve?

Just trying to learn as much as I can about these marvelous machines.

No difference in how the bike runs, unless you happen to remove a vacuum leak
while you're desmogging.

https://www.moccsplace.com/images/pair/pair1.htm

-Mike

[WintrSol]

Is there any difference in how the bike runs?
What’s the job of the pair valve?

Just trying to learn as much as I can about these marvelous machines.

From the service manual: "EXHAUST EMISSION CONTROL SYSTEM (PULSE SECONDARY AIR INJECTION SYSTEM)
The exhaust emission control system consists of a secondary sir supply system which introduces filtered air into the exhaust --- .)
gases in the exhaust port. Fresh air is drawn into the exhaust port whenever there is a negative pressure pulse in the exhaust
system. This charge of fresh air promotes burning of The unburned exhaust gases and changes a considerable amount of
hydrocarbons and carbon monoxide into relatively harmless carbon dioxide and water vapor.
This model has the pulse secondary air injection (PAIR) control valve and PAlR check valves. PAlR check valve prevents
reverse air flow through the system. The PAIR control valve reacts to high intake manifold vacuum and will cut off the -.
supply of fresh air during engine deceleration, thereby preventing afterburn in the exhaust system."

[sandy]

Is there any difference in how the bike runs?
What’s the job of the pair valve?

Just trying to learn as much as I can about these marvelous machines.

The PAIR valves use pulse vacuum to operate them. They pump air from the air cleaner box to the exhaust port immediately after the exhaust valve. The fresh oxygen provides air to complete combustion in the pipes and dilute the emission pollutants.

[pancho]

I keep the  "EXHAUST EMISSION CONTROL SYSTEM" on my bike maintained and in working order. It was designed for these bikes and has a purpose as outlined in the post above. 

To just go in and rip it out over perceived future problems is like removing your wisdom teeth, appendix tonsils, prostrate, nuts and breasts out of fear they might go bad...........      many do        even though they all have a reason for being there.

[Bighead]

I keep the  "EXHAUST EMISSION CONTROL SYSTEM" on my bike maintained and in working order. It was designed for these bikes and has a purpose as outlined in the post above. 

To just go in and rip it out over perceived future problems is like removing your wisdom teeth, appendix tonsils, prostrate, nuts and breasts out of fear they might go bad...........      many do        even though they all have a reason for being there.

Yeah do tell why other than EPA guidelines that all that crap is there?  Answer None.

[98valk]

Is there any difference in how the bike runs?
What’s the job of the pair valve?

Just trying to learn as much as I can about these marvelous machines.

the bike will be three pounds lighter, so a little faster.  more if a california bike with the canister.

[Tfrank59]

So I hear a lot about guys doing a de-smog mod.
Why is it done ?
What’s the benefit?

Educate me please.

So you've read the pros and cons, as have I.  I don't bother fixing what isn't broken or somehow diminishing performance, and my bike with the stock smog stuff (not a CA bike) is working great.  As I've said to others making the same inquiry as yours, I have the desmog kit, so if something changes for the worse on my bike's performance (e.g. a vacuum leak), that's when I'll desmog it.

[Bighead]

So I hear a lot about guys doing a de-smog mod.
Why is it done ?
What’s the benefit?

Educate me please.

), that's when I'll desmog it.

’
How wil this diminish your
Performance? It is wil not.

[Valkorado]

While we're on this subject,  does anyone have a source for good quality vacuum caps?  I was using BonS' for awhile there but I guess he is outta business.

[hubcapsc]

While we're on this subject,  does anyone have a source for good quality vacuum caps?  I was using BonS' for awhile there but I guess he is outta business.

There's a couple of intake runners on a non-desmogged Valkyrie that are capped
with studly OEM caps. I like those caps.

The packs of flimsy vacuum caps at the auto-parts stores work for a while.

You can unscrew the vacuum nipples from the intake runners and put in
a small bolt of the right thread size, that'll plug your vacuum :-) ...

-Mike

[98valk]

While we're on this subject,  does anyone have a source for good quality vacuum caps?  I was using BonS' for awhile there but I guess he is outta business.

redeye uses viton caps

[Tfrank59]

So I hear a lot about guys doing a de-smog mod.
Why is it done ?
What’s the benefit?

Educate me please.

), that's when I'll desmog it.

’
How wil this diminish your
Performance? It is wil not.

a vaccum leak (which could be cured by desmogging) will diminish engine performance.

[RonW]

I used the oem plugs and they're quite sturdy. Though as Valkorado stated using a bolt which would be bulletproof.

[Valkorado]

I used the oem plugs and they're quite sturdy. Though as Valkorado stated using a bolt which would be bulletproof.

Actually that was hubcap's suggestion and I really want to do this.   Has anyone done this and remember what size and thread of bolt will work?   I guess it could be a PIA when synching but not so bad if old nipples saved?

[98valk]

I used the oem plugs and they're quite sturdy. Though as Valkorado stated using a bolt which would be bulletproof.

Actually that was hubcap's suggestion and I really want to do this.   Has anyone done this and remember what size and thread of bolt will work?   I guess it could be a PIA when synching but not so bad if old nipples saved?

search should bring it up.

[RonW]

Somebody must have tried this, as far as, the thread size and pitch.

[hubcapsc]

Somebody must have tried this, as far as, the thread size and pitch.

I haven't done it, but it seems like you could take out a nipple and run
it down to ACE (or your favorite bolt place) and find a bolt with the right
threads that isn't too long pretty easily. And you'd want the threads sealed
too, I guess... RTV?

-Mike

[Jess from VA]

Somebody must have tried this, as far as, the thread size and pitch.

I haven't done it, but it seems like you could take out a nipple and run
it down to ACE (or your favorite bolt place) and find a bolt with the right
threads that isn't too long pretty easily. And you'd want the threads sealed
too, I guess... RTV?

-Mike

You don't want a permanent seal, but RTV won't take the heat (and just cook off).  I'm thinking a hi heat medium-hold thread-locker (not red).

Also, keep in mind the problems using different types of metals (with added heat) causes.

But I'm here to tell you the cheapo auto parts vacuum caps don't last long at all.  They heat up and blow off or blow in two very quickly.  The push and pull forces put on them is significant (assuming you use the throttle).

[hubcapsc]

but RTV won't take the heat

I recently made the poor choice of coating my 8N's new manifold
gasket with high-temp RTV...



I had to take my manifold back off, clean everything up (the rtv was still
like rubber) and use only a new clean gasket on reassembly.

I don't know if it is the appropriate stuff to seal the threads we're
talking about with, but I bet it can handle intake heat... and it
wouldn't be permanent.

-Mike

[Jersey]

On other jobs I've used a short piece of an appropriate sized hose and bolt to block vacuum ports.  It looks like crap, but is very sturdy.  Just use a bolt size that for sure seals the end of the hose.

[Jess from VA]

Mike, I should have known RTV covered more products than the basic pure silicone stuff I use to glue things like my hand grips.  I know THAT stuff can't take heat. 

[SPOFF]

redeye uses viton caps

I replaced all the caps including the OEMs with redeye caps and I replaced the vacuum line to the petcock.

[Paladin528]

redeye sells good vacuum port covers.