Throttle body balance - zero=zero etc...

[MattW]

I'm no engineer obviously and I wouldn't ever even think about making a tool like that. I reckon the pressures would be quite low and difficult to get something accurate enough. Good luck though.

The actual pressure drop over the closed butterfly is probably more than you imagine and easily measured with a simple water manometer (after all a u-tube works just fine for balancing TB's). However I can dial in whatever pressure I like on the flow bench (subject to the limits of my 1.5 kW vac). Remember, I'm only looking for differences between the two TB's - I'm not trying to simulate actual operating pressures.

Sounds like you know exactly what you're doing though.

Nah - I'm making it up as I go along (although I think I have a decent understanding of how the intake system and engine management work).

I've been in engineering (in various flavours) all my working life and have messed with bikes and cars since I could pinch my dad's spanners so I'll try my hand at most stuff (within the limits of my tools and experience). That said I also firmly recognise the value of 'experts' and I wouldn't hesitate to use one when I run out of skill and/or time

 

[Smug]

You need one of these..http://www.ebay.co.uk/itm/Vintage-C...t=UK_Hand_Tools_Equipment&hash=item1c34cb7924 16hrs to go

 

[khpossum]

Or just measure one TB at a time but it'll need careful operation and checking for repeatability.

Nice setup and doing one at a time should do it. The setup is symmetrical, so install both, block one at a time and compare. Sure seems that should do it, but can be checked by calibrating the TB's and then swap them and compare again.

I am not sure though what kind of dP reads you get and how close you have to be to get a good calibration. Should be like a regular TB sync, which can be done just fine.

Nice job!

KP

 

[(RIP) Kaister]

surely a u-tube manometer compares the difference of airflow too ?

 

[MattW]

You need one of these..http://www.ebay.co.uk/itm/Vintage-C...t=UK_Hand_Tools_Equipment&hash=item1c34cb7924 16hrs to go

Thanks.
I did think about one of those. There's a modern version too:
http://www.ebay.co.uk/itm/VW-VOLKSW...526?pt=LH_DefaultDomain_3&hash=item53fb50c6ae
However as I'm only looking for differences in dP across the closed butterflies, I don't really need to know the flow.

Nice setup and doing one at a time should do it. The setup is symmetrical, so install both, block one at a time and compare. Sure seems that should do it, but can be checked by calibrating the TB's and then swap them and compare again.

I am not sure though what kind of dP reads you get and how close you have to be to get a good calibration. Should be like a regular TB sync, which can be done just fine.

Nice job!

KP

Thanks KP

surely a u-tube manometer compares the difference of airflow too ?

If you're talking about a u-tube on a running bike, then yes, difference in airflow can be extrapolated from the difference in pressure at each intake. But you're seeing a cumulative figure resulting from a combination of closed butterfly flow + bleed through the air screws + any air leaks etc.

My air screws are more than a turn different when the U-tube on the running bike says the TB's are balanced. This makes me think that the throttle stops are different and while the intake vacuum on each side is the same, the cylinders are making slightly different power due to the difference in flow (hence the slightly rough running at idle and slight hesitation as the throttles come of their stops and transition to 'cable balance').

What this flow bench *should* let me do is to isolate the dP across the closed butterfly from any other influences (you can't run the bike with closed air screws) and determine once and for all whether the throttle stops have been messed with. Then I can do something about it with a zero-zero. I can also take my time doing it without worrying about melting the bike on tickover.

Who knows?... But it's cost me nothing apart from a little time in the garage - the worst case is I've had to remove the TB's for nothing.

Time will tell...

 

[Steptoe]

People like Steptoe who've been doing this sort of stuff for decades probably have their own techniques developed from years of experience and don't need to do a 'zero-zero'. The rest of us have to do what we can

I work on the very simple principal that they don't need adjusting if they've never been touched.

People do a zero zero when in reality it's another problem they have, and the zero zero just covers up the original problem and they're happy but the underlying problem is still there.
And once they've started messing around instead of finding the original fault it's an ever diminishing circle as they chase thier own arse while adding more problems by chucking everything at it.

Keep it simple. The less you touch the easier it is to find the problem.

 

[(RIP) Kaister]

T


If you're talking about a u-tube on a running bike, then yes, difference in airflow can be extrapolated from the difference in pressure at each intake. But you're seeing a cumulative figure resulting from a combination of closed butterfly flow + bleed through the air screws + any air leaks etc.

My air screws are more than a turn different when the U-tube on the running bike says the TB's are balanced. This makes me think that the throttle stops are different and while the intake vacuum on each side is the same, the cylinders are making slightly different power due to the difference in flow (hence the slightly rough running at idle and slight hesitation as the throttles come of their stops and transition to 'cable balance').

What this flow bench *should* let me do is to isolate the dP across the closed butterfly from any other influences (you can't run the bike with closed air screws) and determine once and for all whether the throttle stops have been messed with. Then I can do something about it with a zero-zero. I can also take my time doing it without worrying about melting the bike on tickover.

Who knows?... But it's cost me nothing apart from a little time in the garage - the worst case is I've had to remove the TB's for nothing.

Time will tell...

what youre ultimately looking for is equal vacuum at idle... a combo of throttle stop plus idle bypass ( brass screw )

using a u tube ..set both brass screws to th

same setting and adjust throttle stops for equal vacuum on the manometer.

then set cables from there up

 

[MattW]

I work on the very simple principal that they don't need adjusting if they've never been touched.

People do a zero zero when in reality it's another problem they have, and the zero zero just covers up the original problem and they're happy but the underlying problem is still there.
And once they've started messing around instead of finding the original fault it's an ever diminishing circle as they chase thier own arse while adding more problems by chucking everything at it.

Keep it simple. The less you touch the easier it is to find the problem.

I agree entirely

The trouble is, I'm pretty sure that the stops on my bike have been touched. It's 19 years old and has had several owners and the TB's have been sent away for new spindle bushes. And as earlier in this thread, the way it runs makes me think the stops might be the cause. With ideas and advice from you and others, I've pretty systematically worked my way through the possible causes. The ridiculous contraption above might help me decide once and for all whether the stops are missadjusted.

what youre ultimately looking for is equal vacuum at idle... a combo of throttle stop plus idle bypass ( brass screw )

using a u tube ..set both brass screws to th

same setting and adjust throttle stops for equal vacuum on the manometer.

then set cables from there up

You've just about described the infamous zero-zero. The only step missing is to set the left hand butterfly to the correct opening from 'zero' using the TPS voltage. You then set the air screws the same and then adjust the right hand stop to match the 'correct' left opening.

 

[Flipfly]

Having recently fecked up be adjusting the throttle locks screws I understand the desire to know it's right.
In the end I bought a secondhand pair of throttle bodies which hadn't been touched.
Unfortunately the right hand TB had a broken throttle cable retainer, so I ended up balancing the throttles using the unmolested TPS side as the reference point.
One of the main things I discovered was the importance of blowing the shite out of the BBS intakes!!! This makes a huge difference and now the bike runs smoothly and cleanly (even with my hamfisted balancing abilities). The amount of shit that came out was startling!!
Before I aquired the spare TB's I actually got it running really nicely by using a carbtune to get close and a little "ear" to fine tune.
Unfortunately fear of it not being right led me to go down the replacement TB route, but I still wonder that if it's running smoothly surely it's running right

Anyway, as far as fuck ups go, it wasn't particularly dear to put right and now I have a couple of smart looking paper weights

 

[Steptoe]

The ridiculous contraption above might help me decide once and for all whether the stops are missadjusted.

.

Have you seen a BMW air flow meter.

They used them to balance the old aircooled twins. It's a simple piece of aparatus, two seperate tubes tube with a guage on the end which looks like the big old compass with a suction pad on that you stuck to a car windscreen - You remove the intake tubes off the throttle bodies and fit the airflow meters. Start the engine and the gauges indicate the airflow.

The bmw owners club may have a set for hire, or a bmw dealer who still has the old factory tools required for aircooled bikes.

 

[cookie]

i don't really see how it's that big a deal if the if the butterflies are ever so slightly out at tickover?

maybe not bang on ideal, but the air bypass screws will even it out, that's what they are there for

 

[MattW]

Flow bench in use:

Could do with squishier gasket material but at first go, the TB's seem to be within a gnats of each other when on the stops.

However, when removing the air screws to clean and check the 'turns', I've discovered that they are only about half a turn each out from closed. The last full balance was done as a part of a service by a bike shop (who assured me they 'know BMWs') because I didn't have time to do it myself. Since then I've only tweaked the screws a little from the settings that the shop left them at.

I'm pretty sure that the screws should be about 2 turns out?...

 

[cookie]

jesusfuckingchristonasledge!

well - as long as you haven't completely wasted your time...


oh, hang on

 

[MattW]

jesusfuckingchristonasledge!

well - as long as you haven't completely wasted your time...


oh, hang on

Yep - should have checked the screws. I knew what they were at last time I did a balance (new throttle cable). Guess I shouldn't have trusted the shop

Still to sure if the air screws will be causing my problems but It'll be running way rich at tickover I'd imagine...

Can anyone confirm the baseline airscrew settings for an 1100? (I've just looked at my notes - they were about two turns out when I last did a balance).

 

[MattW]

Another test - think I've found part of the problem.

This time the vacuum readings for each TB were quite different. Checked the sealing to the 'test platform' and all appeared good. Another test and the readings were still different.

Tested a third time and the readings were about the same as each other.

Thinking to myself WTF is going on here?...

So I took TB's off the test platform and gave them a good inspection under a strong light.

I've just picked out a turn of plastic 'swarf' (for want of a better word) which was wrapped around one of the butterfly shafts. Looks like it has occasionally been interfering with the right hand butterfly closing properly.

 

[MattW]

Ok, all back together and the TB's balanced with the air screws at about 2 1/4 turns out. While balanced at tickover, it ran rough as a dog until I thought about the CO pot which had been set with the air screws wound in too far by the bike shop.

I turned the CO pot clockwise a turn or so (richer?) and it smoothed out a bit and the revs increased but I've no idea what CO it's actually running at. So now I need to sweet talk my local MOT station again and see if they'll stick their emissions tester in my 1100 - I wish you could set it by some other means...

This balancing act between TPS, air screws and CO pot is a tricky sod...

The upshot is that while I didn't really need the flow bench, it has at least confirmed that my throttle stops are unmolested and during the process of testing them I discovered a potential issue with the little piece of swarf so my time wasn't completely wasted

 

[Smug]

Set idle as slow as possible and then adjust Co to achieve maximum revs. Reset idle as slow as possible and reset Co to achieve maximum revs. Trouble will be that if you take too long to do, the engine will get too hot and affect the Co therefore it has to be done very quickly.

 

[MattW]

Set idle as slow as possible and then adjust Co to achieve maximum revs. Reset idle as slow as possible and reset Co to achieve maximum revs. Trouble will be that if you take too long to do, the engine will get too hot and affect the Co therefore it has to be done very quickly.

Thanks Smug - I'll give this a go tomorrow.
From what I've read from Steptoe in the past, it doesn't really matter what the screws are set to, they just set the idle speed (in conjunction with the CO pot). I'll start from where they are now (about 2 turns out but with idle at about 1200) and wind them in with CO pot adjustments as you say above.

When I've got it as good as I can, I'll see if I can persuade the MOT station to check it again.

The annoying thing is that i've got two very expensive combustion analysers which I use in my business but 2% CO is way outside what they can handle (they top out at 0.02%)

 

[newboy]

the Lentini method is the equivalent of putting down a bucket to catch the drips. it masks the problem - but the problem will always be there.

http://www.ncbi.nlm.nih.gov/pubmed/8677053

ouch??

 

[Smug]

You will probably need 3.5-4.0% Co. Trouble is that it will change very quickly when the engine gets warmer.