The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: montmil on August 17, 2010, 05:36:46 PM
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Interesting conversation on the Airheads List today. I have edited names; all except Mr Tom Cutter as he has enough Airhead experience to be consider a guru.
For your enlightenment and edification:
"There's some discussion on another list regarding carburetors mounted vertically at installation or tilted tops-in a bit, perhaps up to 15 degrees.
Rumor is: BMW trained mechs to install the carbs tilted. No one knows why Maybe to ease the cable path?
How do you-all do it and if tilted, why?"
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""Straight Up" carbs are the way I run them. No tilt. If you tilt the carbs, the float level is off, IMHO."
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"Better tell BMW, because they did them all wrong at the factory. Every
new-in-the-crate airhead arrived with the carbs tilted top-inward about
5 degrees or so (i never actually measured the angle.
If you put the carbs vertical, then very slowly rotate the top toward the motor, with
all the intake tube clamps slightly loose, you will feel when everything suddenly comes into alignment.
Also, since all the jets are aligned on the center line of the carb, they are unaffected by the small amount of tilt."
Tom Cutter
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"That very topic was discuted several months ago. I can't remember what the gurus said at the time, but it is a fair bet that they disagreed."
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I orientate them to be vertical, my only concern would be the floats, and that probably is not a concern in the real world .
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I've done it both ways. It makes sense to me that a slight tilt would be better for cable alignment...
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I'm not sure, mine may be slightly tilted - not totally intentionally, but I do try to get them at least somewhat upright
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I can see how a slight tilt in at the top would help the cable runs and even I lean more than 5 deg in the bends so it probably makes no difference to the floats.
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I have always tilted my carbs in. We have corners in Tasmania so the carbs operate at all different sorts of angles at the same time depending on whether I am leaning to the left or the right .....
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I have always tilted my carbs in. We have corners in Tasmania so the carbs operate at all different sorts of angles at the same time depending on whether I am leaning to the left or the right .....
We all have corners Bruce!! i set my flat tops horizontal it doesn't make sense to have the floats tilting on the mounts as most of the time were riding upright, i don't see a problem with the cables.But that's just my humble opinion.
Lou
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Y'all can see how this gets any BMW motorcycle forum ramped up.
I'm a vertical kinda guy but I may try canting the carbs in five degrees and seeing if there's any noticeable difference. I even searched and found my adjustable protractor. Anything to keep those danged cables happy.
Monte
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Y'all can see how this gets any BMW motorcycle forum ramped up.
I'm a vertical kinda guy but I may try canting the carbs in five degrees and seeing if there's any noticeable difference. I even searched and found my adjustable protractor. Anything to keep those danged cables happy.
Monte
Think about it ..you go into a long bend one carb goes horizontal the angle doubles on the other....cannot be right. We will have to Arm wrestle to settle this one.Loser buys the beer.
Mines a Miller Light
Lou
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My intake tubes from the airbox seem to fit a little easier with a slight inward tilt.
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We will have to Arm wrestle to settle this one.Loser buys the beer.
Mines a Miller Light
I'll take that bet Lou, make mine a Shiner Bock in a frosted mug!
Can it really be such a big deal? Does anyone really run out of fuel in a carb going around corners? For example, here's a Youtube video of some crazy high school kid from Stamford, Texas riding the Wall of Death on a 70cc Honda scooter. http://www.youtube.com/watch?v=dN14xrnZwXw&feature=fvst
Wonder if he had to turn his carb to horizontal? ;D
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Cornering should make no difference because centrifugal force balances the angle of lean. Look at it this way: when an aircraft banks for a turn, your coffee does not spill over. Same forces involved.
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Cornering shouldmake no difference because centrifugal force balances the angle of lean
That's a very good point !
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Cornering shouldmake no difference because centrifugal force balances the angle of lean
That's a very good point !
Consider this.. the centrifugal force will be the same on both carbs if they are not in line set at say 10 degrees if you lean the bike over 10 deg bringing one carb horizontal that then puts the other at 20 deg off with that level of tilt plus the centifugal force main jet will be in air pretty quickly.
Re wall of Death once the rider has reached his/her required speed the bike bike runs only at a slight angle to the wall in this case the tight curve of the wall creates alot of centrifugal force overcoming gravity to keep it up there.I was at the Tatton event talking to Kerri about the tecnique.
http://www.wall-of-death.co.uk/index19.html
Lou
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Lou’s point is interesting though maybe the wall of death doesn’t relate exactly to road use. Not sure about that! I think for normal usage what happens is this:
If the carbs are tilted out of the vertical by turning them on the inlet stubs (this is what montmil meant when he started this thread), then it would seem that the fuel level in the float bowls would be “out of true”, that is, no longer horizontal with respect to the road. But I don’t think this is the case. Here’s why: the Bing carb has a two-part float, which swings from the back side (rear wheel side) and works a float needle which is exactly in the center. Therefore I think, with a fuel level tilted left-and-right the result will be upward pressure on one side of the float and downward pressure on the other, so pressures would equalize and the float would just fetch up in its normal position. Further, all the jets including the idle are also along the center line of the carb. So no problem I think. After all -- this is just the situation when you park your R65 on the side stand: the bike is at quite a steep angle and is not moving, so no centrifugal force, but the engine will start and run fine, it is not bothered by the angle.
Is all that right, or not?
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Further, all the jets including the idle are also along the center line of the carb. So no problem I think.
I agree. The main jet even sits in a little well of it's own and has that large washer to minimise the effect of fuel sloshing around in the bowl. Also going back to your aircraft analogy Bings are commonly used in Rotax powered light aircraft so tilting the carbs can't be too much of a problem.