The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Lean_Angle on July 01, 2012, 12:33:00 PM
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Is it possible (or even practical) to use my Twinmax blaancer on my airhead?
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I've got one and have used it on my R65's, but I'm real enthused about using it, I had Carb Stix before and preferred using it, until it broke and I got mercury all over !!!!! .
Members around this site have made their own 'manometers' from scrap lumber, clear tubing and some sort of colored oil, like BMW fork oil, that's purple, or red ATF, something to give you a contrast .
I'm sure a few photos will appear shortly !!!
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... I'm sure a few photos will appear shortly !!!
pdf. file at bottom of this message explains all about the $4.00 manometer. I love it. Use it on both my R65s. Will look for pic later...
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Any differential pressure device will work to balance carbs. A twinmax is convenient but ultimately not as sensitive as a U tube manometer filled with ATF. It would be interesting to do the best balance you could with a Twinmax and then check it with a manometer.
Some say the ATF manometer is too sensitive in that it's hard to get an exact balance. That's because it easily responds to the smallest adjustment that you can possibly make so requires a very careful touch. I'm fine with that even though it means you need to be fairly close to balance before hooking up the manometer or there is a risk of sucking ATF into the engine.
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Just make sure that you have good/fresh batteries in your Twinmax before you use it - it has no linear regulation in the power supply - unless maybe the newest ones added it - so its accuracy and noise rejection are directly related to the battery voltage.
I really like my Morgan Carb Tune from across the Pond - it works very nicely (and I have the 4-carb model so I can use it on other multi cylinder bikes) - it is quite sensitive and works on the rotameter principle (stainless steel slides in glass tubes) so there is no fluid to leak, etc. IT isn't cheap though.
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Ditto what Mike said about the Morgan carbtune. I scored mine from Beemer Boneyard. I tried the ATF unit but like Barry says, unless the carbs are already close to tune it's guaranteed that you'll suck a whole lot of AFT into the carbs. No harm to the bike, but frustrating to use.
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Ive used the ATF manometer even after a carb rebuild and have been able to use it without a problem. One must wait a good ten seconds or more between adjustments for the carbs to finish modifying its vacuum levels. If you are too quick you can get lost one way or another. Also check for balance at cruise RPM's.
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If the fluid in your DIY manometer is moving too quickly to suit you, as was mine, I added smaller tube-within-a-tube restrictors in the lines about twelve inches from the carb vacuum port.
A slightly heavier fluid is also an effective way to modulate too rapid movement.
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(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fi196.photobucket.com%2Falbums%2Faa1%2Fmontmil%2FBMW%2520R65%2FManometer.jpg&hash=8522a9cf7969f12aeefa76eb867c8e7d16126741)
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Thanks for the responses. So where could I tap my twinmax into the post carb side, is there a nipple that I can use or would I have to drill for a tap?
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The vacuum port is the one nearest the outside of the carb capped with a small screw. This is a right hand carb. On the Left hand carb the position of the vacuum port and mixture screw are reversed.
(http://)
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May have a small screw or a short rubber, closed end, tube.
Have you shared the model year of your R65 or did I miss it? That info is always helpful in providing correct response to questions as their are differences through the production run.
Note that most members have their model and year listed in either a signature line or up with the avatar.
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And be sure to replace the screw or the cap when finished balancing the carbs. Helps them run smoother. Right Monte?
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Awesome, was wondering what those little screws were for, noticed them just this morning while setting idle mixture. :)
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The vacuum port is the one nearest the outside of the carb capped with a small screw. This is a right hand carb. On the Left hand carb the position of the vacuum port and mixture screw are reversed.
(http://)
Ok, I see a smaller tube and a bigger tube, I assume the screw capped smaller one is the vacuum tap. What's the bigger one for? Thanks for the very helpful pic! ;)
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It's for idle mixture adjustment .
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It's for idle mixture adjustment .
So I fully loosen the throttle stop bolt at the top and adjust the idle rpm to 850 using the lower idle mixture adjustment? Sorry for the noob questions, she's my first airhead :)
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So I fully loosen the throttle stop bolt at the top and adjust the idle rpm to 850 using the lower idle mixture adjustment?
Lean_Angle,
That's not quite right. You are asking quite a big question here which requires a long explanation to fully understand how to tune the carbs. There are a couple of procedures in the FAQ section you can look at and lots of previous threads to search but in principle you are doing things in a certain order and this assumes a tune up to a running bike rather than setting carbs up from scratch which is more involved.
1. balance the carbs for equal vacuum at idle using the throttle stop screws. This is to ensure both throttle plates are open an equal amount. This is a very sensitive adjustment where the vacuum will respond to the smallest turn of the screw you can make.
2. Adjust the mixture screws for highest idle speed. It might be best to skip this step in the first instance as unless the screws have been recently disturbed there is no reason to suppose they need adjusting and as it's the most subjective adjustment it's the easiest to mess up.
3. If the mixture screws are adjusted go back and do 1. again and if necessary reset the idle speed to the target figure 1050 RPM.
4. Once you have good balance at idle open the throttle slightly and check for equal vacuum balance at 1500 - 2000 RPM. This is checking
for equal pull on the 2 throttle cables. Slacken off the cable adjuster lock nut on top of one carb and turn the adjuster to achieve equal vacuum. This is a very sensitive adjustment so you turn the adjuster by a very small amount and then waiting a few seconds to see the effect on vacuum balance. Tighten the cable adjuster lock nut and once finished ensure both cables have 1 - 2 mm free play with the throttle closed.
That's it in brief but suggest you read some previous threads on the subject before diving in.
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Will do, thank for the tips Barry! :)
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Remember that it takes time to adjust carbs you should cool the cylinders with a shop or similar high volume fan.