Did search. Best simply explained, elegantly demo'ed, page or vid on CV carb sync?

Hello,

Getting my 83 R65 back on the street. Thought I'd dodged a big bullet. Was under a blanket for almost four years. Full tank of four year old gas. Charged battery and it fired up without a hiccup! Took it around the block and it felt like it was in perfect tune. YES!!

I changed the oil/filter/gas/plugs and took it to the next town about 20 mi away. About half way back it started, and continued, shuddering a bit off idle and getting ragged on acceleration. NOOO!! Something slipped into a little carb passage way? Maybe time to check the diaphragm for tears or rot?

I make a few carb tweaks and no improvement. I may just have to dismantle the carbs, but I'm hoping that a bit of carb cleaner and judicious use of compressed air and shop vacuum will dislodge whatever's in the carb's rabbit holes.

Anyway, all that drama aside, I tried to get reacquainted with carb sync. Reread Snow Bum. There HAS to be a more elegant procedure. I'm trying to distill the wealth of information on syncing dual carbs generally (95 percent of it applies across the board) and specifically to our R65s. I own and have used a diy "yardstick" manometer with clear tubing and red transmission fluid. Was happy with the result but that was 4 yrs ago. I'd like to do this right, right from the start. All other preliminary tuning, ignition, valves, etc has been accomplished.

Does anyone have a favorite, simply explained, elegantly demonstrated page or video on carb syncing especially for our model years of CV carbs?

Thank so much.

Welcome to the forum! Snowbum while verbose has all that's really needed. The process comes in three parts:

- mixture adjustment to get each cylinder running at the best mixture. Each mixture screw is adjusted (it controls a gas circuit, so clockwise makes it run leaner) so that the cylinder runs at maximum RPM...then turn it 1/8th turn rich
- idle speed adjustment so each cylinder is idling the same. When a cylinder runs by itself, what RPM can it maintain? In an iterative fashion, each cylinder is shorted to see what the RPM...idle settings are adjusted to achieve synch. It's extremely careful to do the shorting properly so that damage to the ignition system doesn't happen.
- throttle cable adjustment so that the carb slides are pulled evenly. The throttle is rolled on to about 1500-2000 RPM and each cylinder is shorted. The tension in the cable is adjust to synch the RPMs. It is best to slow down the fast cylinder rather than speed up the slow cylinder.

My sig line contains a carb section with a few titles that mention synchronization:

https://forums.bmwmoa.org/showthread.php?75891-On-line-Maintenance-Videos-Mostly-Chris-Harris

Where are you located? Adding that to your profile would help people to see if they're near you...possibly could come by and help out. The Airheads Beemer Club has a number of Tech Days around the country...maybe one is near you.

Welcome to the forum!
I’d feel better if you said you drained the 4 year old gas and looked in the tank? Maybe?
Gary

frascati said:

Does anyone have a favorite, simply explained, elegantly demonstrated page or video on carb syncing especially for our model years of CV carbs?

Thank so much.

Click to expand...

Although I've memorized it, I'd use the instructions that came with my Walus meter.

But, surely there's a BMW club nearby, and if there is there is almost certainly someone with a Twinmax or other better tool than a manometer and experienced with it and willing to help. IMHO forums are a poor substitute for local hands on BMW club members. Despite former claims, you meet the nicest people on BMWs.

Does your Walus look at all like this?



I've located a 35 dollar china clone of that I'm tempted to order. No tax. Free ship.
My tinkering itch makes me want to clone one myself out of a simple vacuum gauge.
If the case is fully sealed an additional port could be added to the case and the bourdon tube
ought to react left or right of zero on a rescaled dial. One cyl to existing port, other cyl to the
cobbled on port.

Maybe a small 1.5 inch version to put right on the bikes dashboard!

Until that 4 year old gas is drained, burned or whatever it takes so that it is no longer in your bike's tank I would not expect the bike to run properly and also would not make assumptions on what the problem might be. The problem is 4 year old gas right now... start there. Depending on storage conditions rubber parts like carb O Rings and diaphragms would be next on my list.

I changed the oil/filter/gas/plugs and took it to the next town about 20 mi away.

Click to expand...

But I agree. I should not have even started it with such gas. But it's done. Now I may have to learn, against my better wishes, the art of bing CV dis/reassembly

I don't know how to use the smiley. I meant to put that at the end of the post, not beginning and cant figure out how to erase it. Hmm.

frascati said:

I don't know how to use the smiley. I meant to put that at the end of the post, not beginning and cant figure out how to erase it. Hmm.

Click to expand...

Just use the Edit Post button below the message box. At the end of the line, find the text characters ": (" [with no space between them]...the forum software converts that into a smiley. Delete those characters. Then save your post.

Is anyone able to tell me the ballpark range, in any useful measure like mbar or psi, of vacuum at the ports of the R65 (for instance) CV carbs? Anywhere from max to min depending on conditions.

Never seen anything like that published. I suppose using the "yardstick" manometer, some back calculations could be made as to the height of fluid that was lifted.

frascati said:

Is anyone able to tell me the ballpark range, in any useful measure like mbar or psi, of vacuum at the ports of the R65 (for instance) CV carbs? Anywhere from max to min depending on conditions.

Click to expand...

I use 'Economy' gauges out of XD-XE Falcons sold here in Australia in the early 80's. They are marked in kPa, have damping built in and the Vac fluctuates around the 30 kPa mark ( from memory ). the vac tends to drop off at higher revs.
I have no idea if they are accurate, although they both read the same ( I have a balance line between them to check ), so I assume they are.

The fact that its around 30 kPa makes its a bit difficult to find Vac gauges with a useful range. -100 to 0 kPa is to too high a range to use (IMHO ), a vented water manometer would need to be too tall and Mercury is too dangerous to use these days.....

I've heard mention that a couple of older US cars may have had something similar. No idea which ones.....

Steve

frascati said:

Is anyone able to tell me the ballpark range, in any useful measure like mbar or psi, of vacuum at the ports of the R65 (for instance) CV carbs? Anywhere from max to min depending on conditions.

Click to expand...

Vacuum measurement can be an area of confusion sometimes since different industries use different methods and units of measurement for different purposes. The most common goes back quite a ways and vacuum was measured using mercury (Hg). Common units are inches/mercury or CM/Hg in metric countries. When using vacuum gauges to tune our bikes we're not really concerned about this measurement and how much it is but rather the balance between cylinders. So the numbers are a bit insignificant but their relation to each other is very significant. Making sure your valves are set perfectly before balancing is a necessary and crucial step. On Oilheads, making sure the idle air screw or "Big Brass Screw aka BBS" is removed, cleaned along with the oriface it screws into and making sure the o ring is good BEFORE you try to balance anything.

I have a Morgan CarbTune that I no longer use that measures vacuum in internal combustion engines. It has 4 ports for 4 cylinder bikes; I never used more than two since my Honda days are well behind me now. The scale on this gauge is marked in CM/Hg or centimeters/mercury. The bottom of the scale is marked 8 and the top is marked 40. When I put it on my R100 vacuum ports I would see readings around 12 to 18 at idle and then 22 to 36 and even higher depending on how much the throttle was open. Again though, I had zero interest in the actual numbers and not even sure they are accurate. What I looked at was the balance between the two as this is what we are after both at idle and just off idle in order to achieve balanced "pull" if you like on both sides thus eliminating vibrations.
You can see a Morgan CarbTune in action here to get some idea: https://www.youtube.com/watch?v=3k5I-Oz3Uug

I now use a Harmonizer as I was lucky enough to get one while it's maker "Grok" on ADVRider was still with us. Sadly they are no longer available and while there have been rumours the device may be produced again there is no sign that is happening other than a development project going on right now. I think it might indicate pressure as well but to be honest, I've never really looked! I just look at the balance. It also indicates RPM using the engine vacuum pulses and has other useful functions as well. I'll have to take a look at the scale next time I use it!

join the Airheads Beemer Club at www.airheads.org lots of local hands on help available almost everywhere.

Friedle