Last job is to balance the carbs, and I can't seem to get it right

[daviee]

sorry but you are wrong read the instructions that come with them it tells you how to calibrate them before use i was in the tuning trade for 10  years so have a fair idea how it works

[BBROWN1664]

Daviee - all they are telling you is how to ensure they are zeroed. Calibration makes sure they read the correct value at a range of pressures from zero to max.
You are correct that you set the needle a hairs breadth away from the stop to ensure that they are all set the same. You are not calibrating them in the true sense though.

[daviee]

no you are wrong zero means nothing on cheep gauges set them all to the first carb theen they will all read the same trust me i have more  experience than you end of story
 

[Disorderlypunk]

im with daviee on this one
if there is a stopper to say zero (1bar) then i would avoid buying them, i would prefer something that does both negative and positive pressure.
when calibrating at home i would use one carb as a control to see they are all giving the same reading (calibrated to each other)
these setups are not that good at giving correct pressure readings but they can be good for making sure they all have the same negative pressure.
if you want accurate pressure readings from 4 individual carbs then the 30 quid kits are not going to cut it.

i will say i dont have one of these relatively cheap set ups myself but have come across them now and again - they can be usefull as long as they are calibrated now and again.

[BBROWN1664]

these setups are not that good at giving correct pressure readings but they can be good for making sure they all have the same negative pressure.

That's my point exactly DP.

Daviee - You may have spent some time professionally or otherwise playing with vacuum gauges but as a qualified aircraft avionics engineer I do know a bit about suck and blow instruments and how they work as well as how they should be calibrated.

for information, the ones with the stop pin need adjusting to be a fraction off the pin when you use them to take the ambient atmospheric pressure into account. When the ambient pressure is lower, the needle will try to move below zero if the last time you used it, the ambient pressure was higher. Just so you know the reason :pokefun

[daviee]

if you no so much about suck and blow you would realise inlet side only sucks thats how it creates a vacuum and if you no  so much about cheep vacuum guages then you will realise im right as you set them on a carb not to zero just off the stop needle that is not where you need them to be accurate you need them to be accurate at the vacuum reading the carb gives but of course being a motorbike mechanic and rolling road operator means nothing to balancing carbs you need to no about aircraft's to do that  :z

[Disorderlypunk]

ok this is getting out of hand very quickly


so setting them all at the same zero would work in a perfect world and most of the time could work
HOWEVER
due to how these sort of things work they need calibrated in use as they have moving parts and springs and all other things that may not be exactly the same as each other and will show a different reading anywhere other than 1 bar


another way to explain  calbration is  2 torque wrench's sitting on a table, one calibrated, one way out
you have no way to know which is which untill you put them under force on a test rig
ok we dont have a test rig for vacuum BUT WE DO we have four different ones of them
each cylinder is its own test rig giving the same vacuum all the time (ish)

[Jamieg285]

Surely the calibration technique depends on what or how you are trying to measure?

If you are measuring actual values of vacuum, then it's important to get them zeroed properly.

If however you're just trying to balance them, it doesn't matter whether the needle starts at 0 or 100, what's important is that all the guages read the same value for the same level of vacuum.

Therefore, in this argument, I side with Daviee.

[Disorderlypunk]

now is the time to take the piss
its time for a poll


https://goo.gl/oENybF

[BBROWN1664]

Surely the calibration technique depends on what or how you are trying to measure?

If you are measuring actual values of vacuum, then it's important to get them zeroed properly.

If however you're just trying to balance them, it doesn't matter whether the needle starts at 0 or 100, what's important is that all the guages read the same value for the same level of vacuum.

Therefore, in this argument, I side with Daviee.

This is what I have been saying.


You set the gauges to all read the same to start with. DO NOT use the stop needle, set the gauges a fraction off it if you have one as that way you know all the gauge as are starting at the same point. Atmospheric pressure will try to move the gauge above or below zero so you set it every time you use it.


following that, chances are your gauges are not accurate anyway and have not been professionally calibrated so you are just looking to see that you have the same reading on all four cylinders.

[daviee]

if you are wanting to measure the actual vacuum them cheep analogue gauges like the ones pictures  are deffo not the way to do it the will get your carbs close if you calibrate them as  i have said but the best is deffo mercury gauges ,

[Hugh Mungus]

If you're wanting to save money by doing the carb balance yourself then buy mercury gauges. They may be more expensive than the other gauges but you're already saving on labour costs at a workshop. So buy some good one's and look after them.


If you've got the cheaper dial gauges you do need to sync them together by using one carb as a bench setting for all four gauges. It is the most accurate way you're going to get a proper reading. Even with mercury gauges it is advisable to do the same to double check that each gauge is giving the same reading as it can point to leaks in the tubes etc.

[darrsi]

Think i paid around 50 odd quid for my Morgan Carbtune gauges, in used but virtually mint condition.
After the second time of use you've technically saved money through labour costs if you were paying a mechanic, plus after the fifth time of using it you actually get a bit handy at using it, plus your learning curve increases even if it can be a slightly frustrating process with adjustment screws in hard to see daft places and twice now i've kinked my fuel tank pipe so it's run out of fuel mid process.
A very worthwhile and satisfying job once done though, the bike runs really sweet afterwards, as long as your air filter, TPS, and bike in general is in reasonably good order whilst it's being adjusted. 

[Hugh Mungus]

It can turn a dog of a bike into a really sweet ride. Always worth doing.

[redmandan]

OK guys, if I can ask some advice again. I've been having another go and I'm stumped again. Made a vid to show my problems:
https://www.youtube.com/watch?v=57CVLvmeIy8
To re-iterate the video: I have the carbs balanced about as well as I can hope/get with the vaccuum gauges I have. The idle screw is now basically redundant. The only way I can change the idle speed is by turning the centre carb balancing screw, just a quarter of a turn changes about 1000 revs and doesn't affect the balance at all. Am I doing something wrong here? Shall I just put it back together and forget about it?


Thanks for any help

[unfazed]

Bet your sorry you asked the first question :lol :lol :lol

Most likely the throttle cables are adjusted incorrectly

Check the adjuster at the handlebar side is backed off fully and if it is loosen the cables at the carburettor end

[His Dudeness]

Ohh the joys of bikes :lol Sounds like it's running on three cylinders when it's idling

[daviee]

you have the setting miles out you need to  take the carbs off and reset all the ajusters to normal and bench sink them first you proll  have the balance adjusters screwed in to  far thats how your idle is not working unscrew them out as far as you can then set your idle adhyster to control idle speed then adjust your balance

[redmandan]

I'm sure you're right daviee but the reality is hard to accept. I just got it all back together, drain/re-fill the coolant again, fiddle about getting the intakes on and off again, getting the fiddly throttle cables off and reattached....

Can anyone tell me exactly how the idle screw works? I understand that the balance screws adjust the pitch of the carb flaps relative to one another. Does the idle screw adjust all flaps equally then, or does it work in another way?

[daviee]

basically the idle adjuster is a throttle stop where the cables turn they pully that opens all the butterflys the same the idle adjuster  stops the pully closing to far if you have all the balance adjusters screwed  to far in the will  hold the buterflys open thats why your idle adjuster is not working and if you have your throttle cable adjusted wrong it can affect it aswell that why i said you need to start from the beginning bench ballance the carbs reset the cables etc as you have prolly everything out from where it should be