Balancing Carbs (with Carbtune II) on 100GS

DCoplin

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C'mon then, some of you out there must have some top tips for getting this bit right.

Have invested in a carbtune doo-dad so I can enter the fun world of carb balancing and am finding it's not quite as straight forward as you would expect.

After half an hour of twiddling this screw and that, the tick over's OK but the bike still runs a bit lumpy at low revs.

I couldn't seem to get much of a change on the guages with the idle/mixture adjust screw and ended up doing most with the throttle stop adjusters - can't help thinking this isn't right.

Anyone got any tried and tested tips for getting the bike running sweetly?

TIA

Dave
 
DCoplin said:
C'mon then, some of you out there must have some top tips for getting this bit right.

Have invested in a carbtune doo-dad so I can enter the fun world of carb balancing and am finding it's not quite as straight forward as you would expect.

After half an hour of twiddling this screw and that, the tick over's OK but the bike still runs a bit lumpy at low revs.

I couldn't seem to get much of a change on the guages with the idle/mixture adjust screw and ended up doing most with the throttle stop adjusters - can't help thinking this isn't right.

Anyone got any tried and tested tips for getting the bike running sweetly?

TIA

Dave

Dave,
Accepting that the valve clearances and the ignition timing are correctly set then start with a warm engine.
first step is to loosen the throttle cable adjusters to give about 4mm of slack cable, connect the Carbtune, start the engine and then adjust the throttle stops until you get about 1200 revs. adjust the each mixture screw until the revs peak, then adjust the throttle stops to get an equal or as near equal reading on the Carbtune.
Next take up the cable adjusters to give 1 - 2mm of slack cable, don't lock the adjusters yet. Rev the engine to 4000 revs using the Carbtune to check if the carbs are opening in sync. Make quarter turn adjustments on the cable adjusters until the carbs open in sync and then lock the adjusters and check and adjust and lock and check until they open in sync with lock cable adjusters.
 
Last reply is the correct way to do it. Tip make sure your engine is warm ride at normal speeds for minimum 20 minute road run. If you try to warm up in the garage you will find that after a run the engine is still out of balance. DO NOT run the engine at 4000 RPM for long you will find that the balance will once again be out and may damage the engine. I lock my throttle with a piece of tape at 3000 RPM for no longer than 60 seconds you should be able to achieve balance if you have everything to hand. Hope this helps
 
Always been a mystery to me how you set the revs with no guage - assume all you folk have PD and they have rev meters ? I generally 'guess'. Spot on about warming bike up, doing it without going anywere just doesn't work, you need a short road ride to suss it.
If it still runs lumpy consider an overhaul kit - just recieved mine, £8 for the pair of carbs all except diaphrams. (Motobins usual next day delivery)
At 65,000 I thought it might smooth things out and improve mpg..........or not ;)
 
I thought all R100 GS's came with clock and rev counter from 1988 on, am I wrong? Final tip with carbtune make sure the rubber hose does not touch your exhaust pipe, they are not heat resistant!
I bought the four column type and am now down to three tubes. 30 years of working on bikes and still do silly tricks!!!
 
Originally posted by Jthornley
I thought all R100 GS's came with clock and rev counter from 1988 on, am I wrong?
Fraid so, 88 bikes had rev counter & clock as extras.91 bikes with the crashbar around the fairing had them as standard.
If you can,t get the bike to idle properly then check the choke gaskets on the sides of the carbs - they deform & pull in air.Mainjet emulsion tubes are another favourite as they get snotted up from the engine breather pipes that vent into each air tube from the airbox.Last you could check your ht leads, should have approx 5 kohms through them
 
SNAP!!!!

Jthornley said:
I thought all R100 GS's came with clock and rev counter from 1988 on, am I wrong? Final tip with carbtune make sure the rubber hose does not touch your exhaust pipe, they are not heat resistant!
I bought the four column type and am now down to three tubes. 30 years of working on bikes and still do silly tricks!!!

Did that with one of my twin columns, wondered why I couldn't get any sensible readings. A cut and splice using about 4" of some spare fuel line from my R75/6 had everything working again.
Good interference fit with no leaks and I don't see why I should replace something I only bought - 25 years ago or so.
 
Always been a mystery to me how you set the revs with no guage

How the "ol' timers" in the club did it was to "shortout" the cylinders one at a time, and adjust each carb independently to get a smooth running bike.

Did you know that a "bent or damaged" spoke is the tool still used by many "BMW Guru's" for balancing engines???

We all know that if we remove a plug wire while the motor is running, we can inflict damage on the ignition can/circuit.

The damaged spoke is cut in half about 4-5 inches long. The threaded end of the spoke threads nicely onto the top of the sparkplug (same thread pattern).
The cut or sharp end is then fitted with the plug wire . Start the bike and use a screw driver, touch the spoke and cylinder head together with the screwdriver thus shorting out that cylinder. This will shortout that cylinder without any damage occuring to the ignition circuit.
This "practise" is still commonly used especially on "older BM's",
where there is "No Hookup" to the carb for any vaccum reading device.
 
Nice tip Rich - must try that one out. Me old R80/7 I used to balance the way you could (one pot at a time), but I noted the manual warnings about the ignition on the "improved" engines and so didn't continue it. If I can find a spoke I'll give that method a go, sounds a damn good tip.;)
(Especially good for 'in the field' maintenance when no carb balancers available)
 
this old chestnut again.

I've failed to get the carbs balanced even close to what I think I think is possible. Please... some advice. BTW it's a 1993 R100GS paralever

The issue I have is with the instruction to "adjust the mixture until the revs peak "
Turning the mixture screw out from the point where it starts to cut out (approx 3/8 turn out) does NOT alter the revs noticebly. I can keep turning to a point (approx 3 turns out ) where it starts to "hunt" or drop revs again but in between the revs are static.

It was running on one cyl - the other plug was shorted

My questions:
Is the peaking of the revs obvious - whether running with one or both cyls? Or do I have to strain to hear it.

Could I set the the screw position to half way betweeen the two points where it hunts? It used work on cars year ago!?

Is it sensible to synchronise the cable adjuster and throttle stop screw smanually ? By removing the carbs and checking for simultaneous movement of the butterfly. Then adjusting tickover by equal turns on the tickover screws.
I don't seem to get much response from the Carbtune. It was a very hot day and I wondered if the rods were sticking


Many thanks
David
 
Does your bike have a 'Y' piece? If it does it is almost impossible to get a smooth running motor below 2,000 RPM. Main concern is to achieve balance at revs, some try 3,000, some 4,000. Balance at road speeds is important rather than a super smooth tick over. I use carbtune and as long as the columns are equal with the engine at reasonable revs the bike will run fine. Check out the diaphragms, they are rubber and do perish. If one is holed or simply old and tired you will chase your derriere for ever. Your bike is 13 years old and a carb overhaul is probably due.

Cable balance is quite easy, undo lock nuts, turn adjuster until revs just start to pick up, turn back 2 complete turns, repeat other side. You will now be quite close, carbtune will allow fine setting.

Hope it helps
 
if twiddling the mixture screw does little, leave it where the manufacturer suggests.

if you have no rev counter, set it where the idle seems comfortable, which is what i do even if it has got a tacho. the book figure seems a bit high for my personal preference.
 
I had a problem once where there was no affect on adjusting the mixture screws (bike had been standing for awhile) turned out the o-rings on the adjuster screws had perished and the pilot drillings were bunged with gunge. I changed the o-rings and cleaned the carbs, which cured the problem. worth a try anyway.
 
Carb tuning

Thanks for the replies

The bike has a collector box, not Y-piece.

I have checked main and pilot jets and both seemed clean, fuel levels equal and no crap in the float bowl. Replacing the o-rings on the pilot jet is a good idea. I haven't had the bike long and although it has a recent service invoice I was surprised to find a couple of minor faults that should have been picked up.

I'll have another go at the week-end and hopefully improve my tuning technique


David
 
Two wheels good,
I'm in StLeonards on sea if you want to contact me I have a good few years experience of balancing these things with a Y piece fitted. 01424721889.
 
carb tune

Thanks Howard,
I'll take you up on that offer sometime soon. I've had some success after practice but improvement is still possible

David
 
C'mon then, some of you out there must have some top tips for getting this bit right.

Have invested in a carbtune doo-dad so I can enter the fun world of carb balancing and am finding it's not quite as straight forward as you would expect.

After half an hour of twiddling this screw and that, the tick over's OK but the bike still runs a bit lumpy at low revs.

I couldn't seem to get much of a change on the guages with the idle/mixture adjust screw and ended up doing most with the throttle stop adjusters - can't help thinking this isn't right.

Anyone got any tried and tested tips for getting the bike running sweetly?

TIA

Dave

Yes, I know this is an old thread, but I'm searching for clues on how to balance carbs. I've had a frustrating morning getting nowhere, basically as per Dave's post above.... :( .

The bike was up at running temp after a 15 minute ride, cable slack checked, timing is good, new spark plugs, engine recently rebuilt so valve clearances and compression good (would that make a difference anyway?), new air filter, jubilee clips on hoses checked and tight, carbs recently cleaned and rebuilt by Steve Scriminger.

Even before trying to check the midrange, I couldn't get the idle anywhere close to balanced :nenau , the difference at least 14mmHg on the Carbtune. Twiddling either idle screw, from closed to a long way out, doesn't seem to close the gap. In the end, both me and the bike were getting too hot, so time to put the tools down and reconsider.

Part of the problem is my own lack of knowledge :eek: (Go on Tarka, do your worst...). I'm busy twiddling away but I've got no idea what's supposed to happen. Is screwing in the idle mixture on either carb supposed to raise or lower revs? Open or close the pressure gap? When Mr Clymer says 'Alternately adjust each idle mixture screw in small increments until the highest engine idle speed is obtained' - WTF does that mean? Screw in or out? 1/4 turns? 1/8 turns? Complete turns? How high could this 'highest..speed' be - 2000? 4000? Redline?

Grrrrrrr..... :spitfire

Any words of wisdon appreciated..... :rob
 
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
 


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