Vacuum hose

[ddebonis]

The brown vacuum hose for my carb's is starting to fall a part. The bike felt like it was running rough when I realized the hose wasn't connected anymore.

I bought some generic 5/32nd in. vacuum hose at the auto parts store.

I assume it's straight forward to replace, but wanted to through it out there in case anyone has any warnings/tips.

Cheers,
Danny

[Tony Smith]

Ok, I'll bite.

I've never seen an airhead carb with a vacuum line.
I'm assuming that it is something to do with compliance with smog laws or some such, in which case I'd suggest replacing the hose by all means, but only after introducing a ball bearing into it to block it off whilst appearing to be fully connected and legal.

If it isn't a "smog" accessory, please post a photo.

[ddebonis]

Yes, it's for the air pollution control. #12 and #13 need to be replaced. http://www.maxbmwmotorcycles.com/fiche/DiagramsMid/B0000324.png?v=04302013

I won't get in trouble if I close it up. They don't do smog tests on old motorcycles here.

But what can I hope to gain from doing that? More horsepower?

[Tony Smith]

I won't get in trouble if I close it up. They don't do smog tests on old motorcycles here.

But what can I hope to gain from doing that? More horsepower?

You might get more horsepower, but I doubt it. What you will get is a lower likelihood of your beast running too lean and therefore lower temps and other "risk factors".
 
If you disable the smog equipment you should check that your carbs are also reset to the "smog equipment free" specifications. Out of curiosity, where do those hoses attach to the Bings? did they simply use the existing vacuum pick up point or provide another?

[Bob_Roller]

All the 'pulse air system' does, is provide air to the exhaust port of the cylinder head .

Just put a vacuum cap on the tubes on the carbs the hose went on .

You don't need to do anything to the carbs, as this air is added after combustion has occured .

A fair amount of owners remove the system from the bike .

[Luca]

Like Tony said, rationale for removal is to keep the bike from running too lean and therefore hot...  especially around the exhaust valves, which don't have a stellar reputation on our bikes.  I also found that the right hand pulse air pipe kept my right carb bowl from coming off.

BMW sells a screw that threads into the vacuum ports.  I prefer to use them because rubber vacuum caps tend to get brittle pretty quickly, and then they can start leaking.  Also, if you ever end up with an intake side backfire, it can blow the rubber caps off (it happened to me once, though I don't have the rubber valve in my airbox).

I use rubber vacuum caps to cover the screws, both because they keep the screws free from grime and I'm paranoid that the screws will rattle out.

You'll also have to somehow seal off the airbox where the vacuum lines go in (fill the hole where the T goes, cap off the T, etc), or you will have an air leak downstream of the filter.

[Bob_Roller]

The air system did nothing to alter the richness or leanness of the fuel air mixture .

It only added 'fresh' air into the exhaust port to help burn unburned fuel in the exhaust gases, to help reduce exhaust emissions .

It had no effect on the carbs what so ever .

[Luca]

You're right, sorry... it does not affect the mixture.

Adding oxygen to the exhaust port does increase heat around the exhaust side of the head, though, which isn't great for the valves and seats.

As best as I can tell, the pulse air system was at least originally added to all their bikes so that BMW didn't have to diddle around with making a California submodel for each bike in their lineup

[Tony Smith]

The air system did nothing to alter the richness or leanness of the fuel air mixture .

It only added 'fresh' air into the exhaust port to help burn unburned fuel in the exhaust gases, to help reduce exhaust emissions .

It had no effect on the carbs what so ever .

Bob, I'm curious, what did the vacuum do? On a purely speculative basis (remember I have never seen a complete system) I imagine that vacuum was bled off to operate a "pulse" valve to use the supersonic pulse sent back down the inlet tract to in turn send a bit of air into the exhaust port of the head.
 
That being the case I would expect some difference in jetting, or at least needle position, but I'm obviously wrong in this as you say there is no difference in the set up of the "normal" and "smog equipped" carbs.
 
One thing is of course obvious, when the vacuum hose fails there will be a bad effect.
 
Is there a publication you are aware of where I can read up on the system?

[Luca]

The vacuum lines are teed together and then hooked up to a valve inside the airbox.

When there is a vacuum in the line, such as during overrun, the valve opens and allows fresh, filtered air through the valve and pipes to the exhaust port, giving any combustibles left in the exhaust the oxygen they need to burn off.

Further burning the exhaust adds more heat to the exhaust system.  It can also lead to popping in the exhaust on deceleration, though the R65 isn't as bad as some other bikes with similar systems (I had a VN750 with a pulse air system that would bang like a howitzer when coming off the throttle at high speed/revs).

[Bob_Roller]

All this system was, is two vacuum activated diaphragm valves in the airbox .

When the vacuum got high enough, the valve would open and allow air from the airbox to get to the exhaust port of the cylinder head via a metal and rubber hose that went from the airbox to the exhaust area of the head, just below the exhaust outlet of the head .

I had a valve go bad within the first year of getting my bike, had a tough time finding the vacuum leak .

I removed the entire system from my bike in 1982 .

I moved to Phoenix in 1993, the state of Arizona required exhaust emission testing for motorcycles in the Phoenix and Tucson metro areas as part of the annual registration process .

My bike passed with no problems with the system removed .

Usually around 25% of the allowable maximum limits for unburned hydrocarbons, nitrous oxide and carbon monoxide .

[marcmax]

If you want to remove it (I did), BoxerCafe has a kit with all the plugs, screws, washers you will need all in one package. When I did mine I ordered all the separate pieces from the local dealer.

http://www.boxercafe.com/startercover.htm

About half way down the page.

[ddebonis]

Thanks very much! Seems like removing the system is the way I want to go.

[Luca]

Since you live in California, I'd keep all the leftover bits just in case you need to have the system installed for emissions testing, and hold off on using some sort of thread locker on the cylinder head plugs until you pass inspection with the system removed.

[Bob_Roller]

If you live in the California, I would leave the system installed until after it is inspected .