Bing Carburettors – pure air system (yes or no?)

[cobbster]

My thirst for knowledge I have a question, the bike (R100GSPD) has a pure air system, as describe in the manual I have, this being –
1. Tubes from filter chamber to exhaust port on both sides, this I understand are for emissions?
2. Two rubber tubes from carbs inlet tract(the place you use for the vacuum gauge) to a connector in front of air filter casing; another tube into filter chamber connected to 2 values in air filter casing, again I understand its purpose is to prevent severe popping and banging when you shut the throttle off.
I did remove the pipes off the bottom of the carbs and fit some screws to plug.(as the lug is threaded on the inside) to blank off. I did notice more popping etc....

I understand that you can remove all the above and blank off? I’ve even got some plugs to do this?

However if someone could advise why you would do that and the benefits I would much appreciate?

Regards

 

[Richard A]

Pure air system is the same as SLS (Sekundär Luft System), I think?

It's a good question. I've been meaning to do this myself on my Basic for a while now, at the same time replacing my needles and jets with pre-SLS versions on the understanding that everything would then match my 'old' R80s, i.e. work properly and I'd get rid of the mild flat spot that SLS fitted engines suffer from.

Trouble is, I cannot for the life of me find the needles and jets I bought for the purpose... grrr.

So, I can only answer that I 'expect' that you'd get better mid-range torque, but I've yet to prove it conclusively to myself.

EDIT: Sorry, just realised that I've introduced an extra variable with the carb changes. So, the answer should be that I could only imagine a benefit with changes to the carbs and the reason I tied this into removal of the SLS is because I had planned to do this at the same time so that I was going to change to a 'proven' setup (i.e. pre-SLS).

So, my revised answer is that I expect you won't see much difference in performance, but could, as you point out, get more popping - which is where I think the carb changes come into play.

I'm imagining that removal of the SLS would be a no-no for the TÜV in Germany, but here it should be no issue, as far as I know, and my environmental conscience wouldn't feel too bad because studies that I have read suggest that the benefit is minimal (certainly when compared to a Cat).

 

[Kenny]

Blank away Tube linking carbs is a self balancing thingymebob...so just balance your carbs and fit s/s screws into the lugs as you say. It is all mainly down to emissions.

 

[Redboots]

+1 for binning it.

There is also a thought that it helps the heads run slightly cooler as there is no "after-burn" with the thing removed.
I noticed no difference in power etc.

Cheers,
John

 

[(RIP) Proff]

Another + for slinging it...

 

[Richard A]

There is also a thought that it helps the heads run slightly cooler as there is no "after-burn" with the thing removed.

Interesting point, although 'anecdotally', I can report that my non-SLS fitted ST's exhausts glow very red after dark, flat out on the motorway, whereas my SLS fitted Basic's exhausts don't so much... but that could be due to different jetting, different exhaust material (mild steel on the ST and stainless on the Basic, I think) so it's probably not a fair comparison.

We'd need to get Rob Farmer and his Thermal Imaging camera on the case.

 

[Redboots]

We'd need to get Rob Farmer and his Thermal Imaging camera on the case.

A fiver says he's done it already

John

 

[cobbster]

Hi Guys,
Thanks for the replies so far, interesting? Prior to carb service without the vacuum pipes on the bottom of the carbs with screws blanking off, the bike popped lots more than when tubes connected.
Although this was carried out prior to service, I doubt it would be any different? Could be wrong but can test next time out.
As mentioned this was my first stab at carburettor works, but my logic thinks that the vacuum helps shut off the carbs, hence no additional air/fuel to burn off (popping etc..). Or as mentioned a different set up of jet / needles etc.... to compensate removal?
Am I right to think that the ‘big spring’ in the top of the carb is also importantl?
What I did notice, in my ‘Heath Robinson way’ the strength of the ‘big spring’ in the top of the carb being different from each other? Is that critical? Didn’t get these in the service kit? One side I had to pull down to fit top of carb, other didn’t?
Interesting....................