Separate idle screws?

[windychris]

Hi guys,

I'm a pretty competent mechanic and generally service my own bikes, but I'm taking on the boxer for the first time this weekend, only ever having serviced Jap stuff before.

Been reading up on the method for synching the carbs, and I think I get all the throttle cable malarky... but am a little confused about it having 2 idle screws, one for each cylinder. There is some comment in there about setting the idle of each cylinder separately, which is the daftest thing I've heard.

What;s the easiest way to go about it? Get the throttles balanced, turn in 1 idle screw to get the idle speed you want, then turn in the other one the same amount? Won;t that send it back out of balance and me into an endless loop of arse chasing?

Help!!

[r550s]

yep, but it's not an endless loop - you only have to go round 2 or three times!
On a four cylinder jap bike all the carbs are mechanically linked in a bank and synchronising them as a once-only is usually good enough. Forever after you can set the idle by the sole stop screw on the end carb in the linkage. The boxer throttles are only linked by cables and an iffy splitter, so, yes, you end up synchronising them pretty regularly. That's why we are always muttering 'twinmax' and 'carbtune' like trolls talking in code. On the plus side, there's only two of them - and the screws are nice and big!

Ps, we're talking about the big brass screws which are AIR BYPASS screws - the idea is to get them A: flowing the same amount of air on tickover (hence the twinmax) & B: together flowing just enough air so's tickover is at the right rpm. You then use the twinmax again, this time to check that the THROTTLE CABLES are opening the butterflies equally. If the twinmax shows that you're flowing the same amount of mixture into each cylinder, at tickover, at itsy bitsy throttle, then at a little bit more than itsy bitsy throttle, etc, then you'll have a nice smooth bike (smooth is a very relative term here ho ho).

If you find yourself drawn to the throttle plate stop screws, lurking near to the cable quadrants, leave well alone...

[JoeC]

Before anybody suggests it, I tried to get a group discount from two dealers on buying bulk Twinmax's but they did not want to know. Said that they did not make enough profit on them to sell them cheaper.

[windychris]

I have a set of carbtune stick gauges and can set up the carbs on my R6 in about 10 mins - I take it these will be ok on the BM?

I've never seen a twinmax....!

[snavetrauts]

Yes I use the Carbtune syste... no problems.... I hang it upside down... you get a little more damping that way

Stuart

BTW, One of my idles is about half a turn out... the other about the norm.. 1.25 turns. Ran beautifully at tickover. Decided to have a fiddle "this cannot be right" i thought. Wish I had left it alone.. now a bit rough.

[oyster]

These film clips are worth saving, they describe the method of servicing the engine.

viewtopic.php?t=4494&highlight=maintainance+maintenance

[Ruffy]

Thank's for sharing those video clips oyster,there very informative,not suggesting i'm going to tackle all of them myself but they show the diy mechanic can tackle most mundane stuff himself!

[twodear]

Thanks to Oyster for posting those clips. I've had to change the front engine cover and was puzzled that the maintenance manual did not address hall sensor plate timing. Now I'm curious why my bike runs at all as I just stuck the sensor plate on there.

Good stuff!

[windychris]

Success, that was way easier than I thought it would be, she's now purring like a kitten again

We only had 1 moment of stress during the service. Refitting the timing hole grommet. After spending 15 mins fishing it out of the engine fins after I dropped it it was poke poke, get in you bastard.... *plunk*.

Oh dear.

Still, I'm gonna work on the theory that a couple of grams of rubber is no match for 20kg of BMW clutch and flywheel I'm certainly not going to go splitting the engine/gearbox joint to try to get it back.

Oh, and I discovered I don't have a 14mm allen socket for the gearbox drain plug. That'll have to wait till next weekend.