Vacuum gauge readings

[davelb]

I have taken the plunge and bought an R65. I should have done it years ago. Very pleased with almost everything about it but there is a little more judder when pulling away then I would like. It smooths out really well above 2000rpm but I think it is carb adjustment I need to concentrate on.
I have been reading and following the advice on the forum and it is starting to improve, I think I just need to be super careful and re check a few times until I get it where I want. My question is about the readings on my vacuum gauges. At 1000 rpm tickover they read about 5 inches. That seems low to me but the bike runs well and the compression is equal and reasonable with no obvious air leaks between the carbs and head. Any thoughts anyone? Thanks.

[montmil]

Welcome to the herd, Dave. And Congrats on your new-to-you R65. Just a note: Please include model year with tech questions. There are some variances between years.

You didn't mention what sort of vacuum gauge you're using but that really doesn't make much difference. You should be looking for an equal balance between the two carbs. Differences in attach tubing i.d. and whatever solution is in the gauge may vary from one instrument to another.

Tuning carbs requires that the engine be at full operating temperature, A warm-up ride around the block won't do it. 10-15 miles is more like it. Also, be sure the valve lash is properly set and timing is spot on. These basic items have a major effect on carb tuning.

[Bob_Roller]

You can probably get rid of the vacuum gauge set up and make a simple manometer using clear tubing, a length of wood and a colored oil .
I'll never go back to any other method of carb synchronizing .

[Barry]

Dave,

Sounds like you are measuring individual vacuum readings with a gauge marked  in inches of mercury.  Those gauges have a value but they are not sensitive enough to measure the difference between cylinders when balancing carbs. A U tube manometer filled with ATF is vastly more sensitive.

[davelb]

Gosh; thanks for all of the feedback.
Some useful things to consider and try out. (It is a 79 model)
I have checked the valve clearance and then put the strobe gun on to check the timing. Clearance is good and the timing marks are very stable for the age of the machine. The timing advances as it should.
It sounds as if I need to ditch the gauges and get some tube. I will pop out tomorrow and give that a try instead. I will let you all know how I get on.
(I love the colour of your R65 Barry, what is the colour please?)

[Barry]

That's the original paint and it's called silver beige metallic.
This is a better representation of the colour taken in daylight without flash.

[davelb]

Thanks Barry. I think your bike looks stunning and I am looking forward to restoring mine to something like this condition. I can't see a colour code on mine to tell me what the original paint would have been but it has the brown seat and I think that silver beige will go very well with that.
That will all have to wait as I want to spend the last of the Summer (what Summer!) in riding and getting the mechanical side sorted. I will be taking it all to pieces and making it pretty once I know that everything is sound.
Heading off for some plastic tube so I can try to balance the carbs.

Anything else I should be checking out as a new BMW owner?
Thanks in advance.

[Barry]

It did look quite good in that pic but it's been ridden through 6 or 7 winters since then. The seat in that 2nd pic has the original brown cover although I've since fitted a black one.

[davelb]

OK folks, update as promised.
Went to get tube to make a manometer and put 20 miles on to warm her up as Monte suggested.
When I got back I plugged in the old gauges to see how she looked, not too bad, a close but not exactly balanced reading. Then I plugged in the manometer and started her up. Whoosh, all the oil shot through the top on on one side. Clearly the manometer is significantly more sensitive than the gauges! Luckily none of the oil got as far as the carb.
I set about trying to balance on the idle adjustment screw using the gauges to get a closer balance but one side makes no difference at all when the screw is wound out and in. The float bowl has a nasty brown powder like substance in the bottom so I guess it is time to clean out the carb.

(Does anyone know what colours were used with the brown seats?)

[Bob_Roller]

Sounds like you need to clean the carbs .

The carb that shows no change when you move the screw, I'm assuming, it's the idle mixture adjustment, you need to remove the idle jet, it's just inside the bowl area, has a slot for a screwdriver, the metering orifice is at the very end and when it's clear, it's hard to tell .

There are two holes drilled in the body of the jet, these holes need to be closed off, then spray carb cleaner to see if it comes out the other end .

Even when it's clear, it's hard to tell, the brass tube has two holes drilled in it at 90 degree angles, you need to close off those holes, then spray carb cleaner to see if the end is open or not .

I chased this problem on my '81 R65 for a while, until I figured it out .

If you do get oil into the carbs, it won't cause any harm, just may smoke a bit, until it burns off .

[Barry]

You may well need to fine tun the idle mixture but if the vacuum balance is that far out then you should adjust the throttle stop screws first to get equal vacuum. Turn the throttle stop screw anti clockwise on the side that shot up. You will find the smallest possible adjustment of the throttle stop screw will impact on vacuum balance so use very small increments.

Carb tuning is a process of homing in on the best settings so you may need to go through several cycles of  idle mixture adjustment and vacuum balance.  If you use ATF or two stroke oil in the manometer a small amount getting into the carbs won't be the end of the world. It may look like it's moving fast and a lot of oil would enter the carb but as soon as the liquid hits the small orifice in the venturi it would slow down dramatically.


All the79's I've ever seen had brown seats and I didn't know they did black ones from the factory. Got to say I prefer black.

[montmil]

You can slow down the often too quick fluid movement in your DIY manometer by inserting short lengths of a smaller i.d. tubing into the larger, primary tubing. Match up the primary vinyl tubing's i.d. with the smaller tubing o.d.

A small tubing length about one-inch will do it. I added mine about 12-inches from the vacuum take off port.

If you have some pressure on the butterflys from the idle adjust screws, this could hold the butterflys open a wee bit and mess with your idle air mixture adjust attempts.

[davelb]

Thanks everyone, there is plenty there to look at and try out. I have taken off the carb and it is buzzing away in an ultrasonic tank at the moment. It is so grubby I think I am going to give the "good" carb a bath too. I will go and get some carb cleaner spray in the morning and give them a shot of that before reassembly  too as Bob mentioned. While that is happening I am going to make a small reducer as Monte suggests.
Forecast for the weather looks good in the morning so I hope it will be back together and ready to ride!
Will update when done.

[Barry]

Technical name is a snubber. I've never found them necessary but they are a good idea.

With the carbs off are you intending to go back to base settings i.e. whatever the stock turns out are for your idle mixture screws and turns in for the throttle stops ?

If so it's a good idea to check the concentricity of the butterflies in the bore by holding the carbs up to the light with the butterflies fully closed. If they are not dead centre it will show as an uneven ring of light and can be corrected by slightly loosening the two screws. They will likely be peened but you can usually slacken them a fraction and tighten them up again.

The other essential base setting is float bowl levels and unless the floats are new you must ensure they both weigh the same otherwise carb tuning is more problematic if not impossible to balance in terms of mixture. Anything between 12.5 - 13 grams new and up to 14 or at a stretch 15 grams is just about serviceable but they must be the same or you'll never get equal mixtures across the range.

[davelb]

Ok folks, here is the update. I cleaned both carbs very carefully and gave them a good zoosh with carb cleaner as Rob suggested and blew them through with the airline all airways are now clear. I inspected both carbs and set to base settings as Barry suggested. I have not weighed the floats yet but I am borrowing a very sensitive scale to do this early next week. Float levels are good to go.
As I reassembled I noticed that a previous owner seems to have reassembled the cold start device 180 degrees out, the arm was OK but the drum inside had the holes and slots in a different position. I took off the arm and moved it round to match.


 I think that is right, at least it was different to the "good" carb so I set them both as the the arrangement on the good carb.
Straight from start up she sounded way better and lots less jumpy than a jelly on a pogo stick!
I took it for a good long warm up and then I got a level on the gauges before changing onto the new and improved manometer.
Oil stayed in tube and I have done my first set up, I suspect it will be the first of a cycle as Barry said.

Oh my word, it is a different machine.
I liked it before, I love it now. Thanks all for the good advice.
(Ride and tweak with a check on float weights next week.)

The only thing is that with my head against the engine for so long I have noticed a slight rattle from what I think is the clutch release bearing. It goes when the clutch is pulled in. Is my diagnosis correct or is it likely to be anything else?