how to use a carbtune ?

[Captain Black]

Bought a carbtune kit to try and balance my carbs on my bikes this week. My first problem is the instructions it comes with just explain how to set it up and not how to actually use it. Does anyone know of a guide as to how to connect it and what i should be doing to achieve the best results in terms of adjustments etc? Anything in print that i could follow as a guide would be great. I did get slightly concerned when the all to brief manual said to hang the thing upside down for BMW'S ........Thanks.

 

[(RIP) pastyman]

Yup, thats right. for bms you hang it upside down, that is with pipes hanging ndown. I hang it from the handle on the left side of the bike. make sure the little baffles are in place in the tubes othyerwise you will get huge fluctuations when the engine is ticking over.
Under the carbs there is a short rubber tube, pull this off and you wil see a small screw. take this out ( dont lose it) and connect the ends of the pipes to the carbtune there. start the engine and watch the mercury in the carbtune. the two should be level though at low revs they will "pump" like mad. trey it and you will soon get the idea. you will also see that as you screw the mixture screws in or out how it affects the mercury column.
Will have a look tomorrow to see if I have a copy of the instructions.

 

[Redboots]

Some Have you got this sheet
?

John

 

[cookie]

with my carbtune, it's very rare that it needs to be used upside down, even on BMWs.

 

[(RIP) pastyman]

Found the instructions but Redboots has beaten me to it..

 

[Steptoe]

Do you have the mercury carbtune or the stainless rod version ?

Anyway -Do not turn the mercury version upside down.

 

[MikeP]

Anyway -Do not turn the mercury version upside down.

I have the mercury version. Do I have to turn my bike upside down instead?

 

[fayeslane]

I have the mercury version. Do I have to turn my bike upside down instead?

No, just move down here

 

[Richard A]

Captain Black, as you say, (for the stainless rod version only) Morgan suggests that for bikes which may produce an idle vacuum of 8cmHg or less (for which he gives R-series BMs and 2-strokes as examples) it will be better to hang the gauge upside down. The stainless rods are sprung, so upside down the weight of the rods pulls on the springs and settle at a higher cmHg reading than might be 'true'. However, the actual cmHg markings (when operating right way up) are not intended to be taken as super accurate. The strength of the Carbtune design is in its ability to show accurate comparisons (i.e. relative values) rather than absolute values.

I've only recently acquired the new type of Carbtune (having somehow temporarily mislaid my old mercury set - and also because I was interested to try the new Carbtune as it looked to be less hassle) and haven't done any of my R80s yet, but they work fine right way up on my Morini.

I think Morgan explains the rules of thumb for the actual carburettor balancing step and how to use the tool quite well. The key thing is that balancing comes at the end of all previous tune up actions, ignition tuning etc. but particularly after setting the base mixture settings for each carb.

With R-series cable stretch probably pays a greater part in the whole picture and sometimes I struggle to find a compromise between synchronous lifting of the butterflies off the stops with mixture affected readings that occur just above tickover. Once the throttles are open more than a crack, however, the mixture settings play a decreasing role in the relative vacuum readings as the engine revs rise.

 

[Captain Black]

Thanks for all the advice. Ive set up the carbtune, just need some dry weather to wheel the bike out and have a play now. I have serviced the bike, tappet service/plugs/filter/oils etc so i hope it will give a good reading, it seems ok but the idle is a little on the slow side, so need to suss out how to bring the tick over up a tiny bit.

 

[cristhemuso]

Thanks for all the advice. Ive set up the carbtune, just need some dry weather to wheel the bike out and have a play now. I have serviced the bike, tappet service/plugs/filter/oils etc so i hope it will give a good reading, it seems ok but the idle is a little on the slow side, so need to suss out how to bring the tick over up a tiny bit.

Hi. I have had a gs for 20 odd years and I have the original murcury carb tuner. Basically I never bother hooking them up to balance up my gs. The only balancing necessary is the initial pick up. The bing CV carbs effectively balance themselves at part throttle above idle. All you need to do is, at tickover, reach under the carb and push up on the linkage and check that the engine goes "out of balance" the same amount when you push a similar amount right and left to take it off idle. (sounds odd but I hope you understand) Honestly the transition from tickover to partial throttle is all the balancing you need to do and it is very easy and quick. If you balance at part throttle the bike will feel dog rough at transition from tick over to to part throttle. If the bike still feels rough remove the float bowls and the main jet and clean out all the crap in the emulsion tube. I don't know where it comes from but it does mean you cant make the carbs balance.

 

[cristhemuso]

Hi. I have had a gs for 20 odd years and I have the original murcury carb tuner. Basically I never bother hooking them up to balance up my gs. The only balancing necessary is the initial pick up. The bing CV carbs effectively balance themselves at part throttle above idle. All you need to do is, at tickover, reach under the carb and push up on the linkage and check that the engine goes "out of balance" the same amount when you push a similar amount right and left to take it off idle. (sounds odd but I hope you understand) Honestly the transition from tickover to partial throttle is all the balancing you need to do and it is very easy and quick. If you balance at part throttle the bike will feel dog rough at transition from tick over to to part throttle. If the bike still feels rough remove the float bowls and the main jet and clean out all the crap in the emulsion tube. I don't know where it comes from but it does mean you cant make the carbs balance.

Sorry forgot to say. Tickover balance is best set as per my previous post. Adust the idle stops with a screwdriver. The off idle balance is adjusted by adjusting the cable length on one side only such that, pressing on the throttle linkage arm whilst holding the throttle open a smidge on the twistgrip, causes the engine to go out of balance a similar amount right and left (by ear). More difficult to describe than do. Dont bother with gauges. You will get a better balance by feel honest!