Balancing Carbs (with Carbtune II) on 100GS

Mercury manometer

Rob, hi

You say that the old fashioned mercury manometers are the best (easiest) tool to balance the carbs. I have come across a bottle of Mercury, about 600g in weight, would that be enough to make a manometer, and do you or anyone else have a simple diagram or instructions with dimensions on how to make one?

Thanks

Nick

PS Maybe this could be posted in the Airhead Tech section
 
nick.ct said:
Rob, hi

You say that the old fashioned mercury manometers are the best (easiest) tool to balance the carbs. I have come across a bottle of Mercury, about 600g in weight, would that be enough to make a manometer, and do you or anyone else have a simple diagram or instructions with dimensions on how to make one?

Thanks

Nick

PS Maybe this could be posted in the Airhead Tech section
Click to expand...


Keep that stuff WELL away from any Ali surface, i once saw a Landrover
(ex army) that had had a mercury vile dropped in the back... New body please sir. Took no more than a week to eat the whole Ali bodywork, an snow good washing with water cos it gets into the Ali in seconds....

I think 600g's should do for two or three...:thumb2
 
nick.ct said:
Rob, hi

You say that the old fashioned mercury manometers are the best (easiest) tool to balance the carbs. I have come across a bottle of Mercury, about 600g in weight, would that be enough to make a manometer,
Click to expand...

You'll get a few out of 600g.

Want to sell some, i could do with a top up. My mercury guages are a little low after 27 years use. ;)
 
Rob Farmer said:
Andy,

Set the mixture screw to their standard settings, 1.25 to 1,5 usually, then when the engines warmed up slowly turn one of the mixture screws out a little, you should hear the revs pick up, just turn it slowly out until the revs peak, if you go too far the revs slow down, if this happens turn the mixture screw in until it peaks again. Don't worry about the actual revs. Now do the other side the same. Once you are at optimum tick over revs on both sides fit the balance gauges and balance them up using the tick over screws and set them to a slightly low tick over. The bike will probably be over heating at this point so go for a spin round the block to get it to it's normal temperature and then see how it ticks over. Once you are happy that it ticks over properly you can then balance at higher revs using the throttle cables. You will probably have a problem on your 80 with the carbtune rods disappearing from view - you can turn them upside down to assist.
Click to expand...

That did it! :clap:clap:clap

Cheers Rob - carbs now balanced, made a HUGE difference to the bike.

:beerjug:

Andy
 
Rob Farmer said:
Andy,

Set the mixture screw to their standard settings, 1.25 to 1,5 usually, then when the engines warmed up slowly turn one of the mixture screws out a little, you should hear the revs pick up, just turn it slowly out until the revs peak, if you go too far the revs slow down, if this happens turn the mixture screw in until it peaks again. Don't worry about the actual revs. Now do the other side the same. Once you are at optimum tick over revs on both sides fit the balance gauges and balance them up using the tick over screws and set them to a slightly low tick over. The bike will probably be over heating at this point so go for a spin round the block to get it to it's normal temperature and then see how it ticks over. Once you are happy that it ticks over properly you can then balance at higher revs using the throttle cables. You will probably have a problem on your 80 with the carbtune rods disappearing from view - you can turn them upside down to assist.

TBH the carbtune IIs are a pile of poo. The best balancing device is an original mercury filled gauge but this are no longer available. The next best thing is a manometer. see here http://www.ukgser.com/forums/showthread.php?t=24609&highlight=manometer
Click to expand...

1.25 to 1.5 what? Turns out from home?
My bike wouldn't idle so I've removed and cleaned/overhauled the carbs today but didn't have time to finish the job.
My mixture screws were set to 3/4 turn out on the L/H carb and 5/8 turn on the R/H carb. Also the O rings were all hardened and squared off, the choke gaskets were sucked in as mentioned by another poster, the L/H choke was quite stiff and there was some crap around the main jets.
Hopefully it should be much improved. Tomorrow I shall have to invest in a carb balancing tool and fire it up.
Can someone confirm the correct amount of turns out the mixture screws need to be?
Bing 32mm constant depression carbs, BTW. :thumb2
 
1.25 to 1.5 what? Turns out from home? - yes

Can someone confirm the correct amount of turns out the mixture screws need to be? - see above - then follow rob's advice :D
 
What with recent events I haven't had much of a chance to do anything much but I did strip and overhaul the carbs the other week and tonight I fired the beastie up for the first time. After waiting for the carbs to fill up it ran sweetly on full choke, sweetly on half choke and sweetly on idle. It was too late in the day to go for a spin and then balance the carbs with my home-made manometer, but it seems that the standard settings are certainly a good benchmark.
 
S'funny. I have an R80 with a 1000cc kit on it but the 80 (32mm?) carbs. The carbs seem to stay in ballance for ages, far longer that the "True" R100 GS I had a few years back. It seems to be very smooth low down for a 1000cc. It also has a Y piece fitted but I've never seen one like mine fitted to any other GS. It is a true "Y" and not an "h" shape that I've seen on other bikes. The previous owner told me that it was made here in Germany but thats all I know. Not sure what that has to do with the carbs staying in ballance however.
 
Took it for a spin to warm it up today. Revs were too high so I dropped them down then went about balancing the carbs. I think they are somewhere near now, at idle certainly, but when I open the throttle the left pot has more (or is it less? :confused:) vacuum than the right, i.e. the left sucks the oil up. Should I wind the throttle open to a likely position and balance the carbs at this point? This would seem logical as the throttle spends more time open than closed.
Suggestions?
 
all you've done is balance the throttle stop screws.

you now need to balance the cables using the adjusters
 
Thank you, birthday geezer.
So, I've got it balanced at idle. How do I proceed? Does the left cable need some slack in it or some taking out?
This is my first time at balancing carbs as you may be able to tell.
 
higher liquid level = more vacuum = more closed carb

therefore - screw the cable adjuster in / down or the rhs up - depending on revs and cable slack.

make sure you have cable slack all the time - about 2-3mm - then move bars lock to lock to check.

check idle mixture for highest revs on the idle screw
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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