Another carb synch thread

[bangpaul]

I haven't had the time to get around to the little jobs lately, so I got a mechanic to replace the drive shaft boot for me recently. I asked him to tune the carbs while he was at it, but now it's taking a long time for the idle to return to normal. Otherwise the bike is running a lot better.

I rang and he told me to warm the bike up and then just incrementally tighten the screws beneath the carbs until the problem goes away. Not having any instruments to properly balance the carbs I'm bit weary of touching them.

I seem to remember Bob, or possibly Monte, describing a process in which you loosen the screws until the idle cuts out, and then tighten them until you get the correct idle. Is this right? I can't find the thread now.

[montmil]

Your mechanic may not have properly warmed up the engine prior to his tweaks on your Bings.

Take a look at the bottom of your carburetors. Go ahead... lay on the floor as it's easier. Note the idle mixture screws. You will need a small, flat blade screwdriver to match the slot in the jet screw.

Next, go for a 15-20 mile ride to get the bike up to temp. Upon returning home, set a large fan in front of the bike and with the engine still hot and still running...

Lay back down and use the little screwdriver to turn each idle jet screw clockwise no more than the thickness of the tip of screwdriver's blade. Blip the throttle and listen for results. Idle drop a bit? Your heading in the right direction. Try again while keeping the tweaks equal on both carbs.

It has been my experience than most idle jet screws are open a bit too much.

Also, when I do this little drill, and before I begin, I put a pencil mark on the carb body that will permit me to return to the original setting.

Give it a whirl, mate. [smiley=thumbsup.gif]

[Barry]

I rang and he told me to warm the bike up and then just incrementally tighten the screws beneath the carbs until the problem goes away.

If you do what your mechanic suggests (he's implying that the idle mixture screws are set too rich) the idle speed should rise a little as the screws are turned in to the optimum mixture. The object of adjusting the idle mixture screws is always to achieve maximum idle speed. You are probably recalling the technique of turning the idle mixture screws in until the idle speed starts to slow and then turning them out until the idle speed starts to slow. The optimum setting should be half way between the two. In practice I find it better to turn them in until the idle starts to slow then back out again only just enough for the idle to speed up again. You may then need to back off the throttle stop screws on top of the carbs to lower the idle speed to the correct value. Turn them out anti-clockwise by exactly equal amounts until you have the idle speed at around 1050rpm. Ideally then check the idle mixture screws again but if your throttle stop screw adjustments have been very small I wouldn't bother.

Agree with Monte that you should record the screw positions in some way so that if things get messed up you can go back and start again.

[Milo_357]

If someone can point us at a GOOD (ie has pictures!) guide to syncing the carbs, I'd sure appreciate it.

Dell

[Barry]

If someone can point us at a GOOD (ie has pictures!) guide to syncing the carbs, I'd sure appreciate it.
 

I've had a look around the Internet and can't find a carb tuning article with pictures. Maybe an exploded diagram of the carb indicating which adjusting screw was which would help with the written tuning process.

The other option is that there are several tuning videos on you tube if you search for something like airhead carb balancing or tuning. No need to be restricted to R65's. Tuning any airhead with Bing CV carbs is the same in principle.

[Adrian]

Hi there bangpaul - a couple of other things that I think might be a good idea to check are :
1. Your throttle assembly at the h'bars is clean and well lubricated.
2. No fraying cables anywhere between the throttle and the carby.
3. The splitter box under the tank must be completely clean and dry and without any lubricant. This will only clog up the box.
4. Make sure both the splitter box adjuster is correctly adjusted - leaving just a fraction of "up and down" movement of the upper cable outer - the carby cables are adjusted so that the outers have a tiny amount of movement up and down and also allow both throttle links to move together with no discernable delay between them when they move. That is when you turn the h'bar throttle.
I balance my carbs perhaps 3 or 4 times a year using a device I bought called Carbtune Pro. It uses tubes with steel slides and vacumn tubes that attach to the underside of the carbies. and work so much better than my old vacum dials. This is the net address - www.mcp.com.au.
I know everyone has there different methods but I've always set the air screws to their recommended position and will only adjust them if I find the plug colours are not correct after a long ride. So far - even though my carbies are from 1984 - this has always given me acceptable results.
Hope this helps mate - I see you're a fellow aussie - have a good day and great riding mate.

[Milo_357]

If someone can point us at a GOOD (ie has pictures!) guide to syncing the carbs, I'd sure appreciate it.
 

I've had a look around the Internet and can't find a carb tuning article with pictures. Maybe an exploded diagram of the carb indicating which adjusting screw was which would help with the written tuning process.

The other option is that there are several tuning videos on you tube if you search for something like airhead carb balancing or tuning. No need to be restricted to R65's. Tuning any airhead with Bing CV carbs is the same in principle.

You've seen carb synch vies on YouTube?  Really? Do you have a link by chance?

Thanks,

Dell

[wa1udg]

I have little red paint dots an all my carb adjustments.  I am not sure if they are factory or were put there by a legendary BMW mechanic, Avedis, ("OV"  for short) who worked  on the bike.  

[Barry]

Yes if you do a search there are a few.

Having now watched some of them I can't say how much use they will be as an instruction on how to do it. I thought the best one was for an oilhead which is similar enough in principle. At least the guy attempted to do a decent job of it.

Last one is a Rotax Bing but worth watching for location of throttle stop screw and idle mixture screw.

http://www.youtube.com/watch?v=nEE508WzNC8&feature=related

http://www.youtube.com/watch?v=v97Vvfk0uNI

http://www.youtube.com/watch?v=pu3cQh1EErQ

[Dizerens5]

I'm in the middle of experimenting but it does seem that the R65 reacts to amazingly small changes in idle mixture screws. At least on spark plug readings. About 1/8 turn produces big difference. Surprising when you think this engine doesn't care much about exact ignition setting. We live and learn.

[Barry]

it does seem that the R65 reacts to amazingly small changes in idle mixture screws.

That's very much been my experience and one of the secrets of tuning our carbs properly. When the idle mixture screw baseline setting is 1/2 turn out then 1/8 of turn is quite a big change so it will have a noticeable effect on MPG too.  I go in changes of the width of the screw slot.

This is also why I have said many times to ignore tuning procedures which say " find the sweet spot and then turn another 1/4 turn out" That might be reasonable advice for a carb where the baseline setting is 2 or 2 1/2 turns out but as a generalisation applied to our carb settings it's nonsense.

[R65Singh]

That's very much been my experience and one of the secrets of tuning our carbs properly. When the idle mixture screw baseline setting is 1/2 turn out then 1/8 of turn is quite a big change so it will have a noticeable effect on MPG too.I go in changes of the width of the screw slot.

This is also why I have said many times to ignore tuning procedures which say " find the sweet spot and then turn another 1/4 turn out" That might be reasonable advice for a carb where the baseline setting is 2 or 2 1/2 turns out but as a generalisation applied to our carb settings it's nonsense.  

I followed what Berry said in one of his previous posts about mixture screw adjustment and he is right on.  Mixture screw is very very sensitive on our bikes and little change will effect in a big way.

I sync my carbs using both methods; Manometer and Plug shorting, surprisingly results are not the same.  I mean to say if the both carbs show same suction the bike stills runs a bit rough but with Plug shorting it runs more smoother.  I don't know the exact reason for that.  However I still can't hold rpm around 2200 (when parked).  It will either jump to 3000 or stay around 1800.  But Berry's method to get the best fuel mileage is right on the money, I like his first hand experience and the way he spits out facts.  

[Milo_357]

Just for some clarification,

When using a manometer to balance the carbs, you make the adjust 1st by eye on the idle with the cable adjust first, then if one side of the manometer is higher than the other, then ADJUST the cable adjust to balance, then FINALLY fine turn using the Idle adjust?

Also:

1)how many turns back from flat should the idle adjust screw be?
2)how many turns back from flat should the cable adjust screw be?
3)how many turns back from flat should the main jet screw be? I have mine at 1.25 turns.

Thanks for the clarification.  Barry, thanks for the great vids!

Dell

[nhmaf]

You want the cables to pull the same on both sides at the same time, and ideally, have 1-2mm of free play on each.   You definitely want to get/verify that the cables are synched before you try turning the screws and doing the manometer thing.   I first set the cables, then try to adjust the idle for best idle.   Then I hook up the rotameters and try to get things balanced as well as possible at idle and at, say 4000 RPM.   I think it is more useful to try to get the carbs as close as possible at some useful cruising RPM than at idle, as you're more likely to notice unwanted vibration, etc. while cruising, and the bike is going to vibrate some anyway at a stoplight, so if I have to favor/split the difference inadjustments, I lean toward making things better at the useful RPM than idle.   I can generally get things within 1cm Hg pressure balance between both carbs at idle and 4000 RPM.

[Milo_357]

You want the cables to pull the same on both sides at the same time, and ideally, have 1-2mm of free play on each.   You definitely want to get/verify that the cables are synched before you try turning the screws and doing the manometer thing.   I first set the cables, then try to adjust the idle for best idle.   Then I hook up the rotameters and try to get things balanced as well as possible at idle and at, say 4000 RPM.   I think it is more useful to try to get the carbs as close as possible at some useful cruising RPM than at idle, as you're more likely to notice unwanted vibration, etc. while cruising, and the bike is going to vibrate some anyway at a stoplight, so if I have to favor/split the difference inadjustments, I lean toward making things better at the useful RPM than idle.   I can generally get things within 1cm Hg pressure balance between both carbs at idle and 4000 RPM.

Hey nhmaf, thanks for the feedback... question.  "1-2mm of free play" Free play where exactly in the line? On the throttle up down?  What is a rotameter, and what does it do?  Am I not adjusting the items I mentioned above

Again, thank you for the help,

Dell