Carb Rebuild

Hi all,

I'm gearing up to rebuild the carbs on my "new" R75/7 in January (my first). Bob's BMW sells this deluxe kit, which includes parts for a complete rebuild for both carbs: https://tinyurl.com/y8bl3crl

Has anybody here used this kit? Thoughts?

Bing offers a different float that they claim is more resistant to ethanol. Thoughts on this?

Any other advice you can provide would be very welcomed.

Thanks!

Wow, that's expensive!! IMO there's lots of parts in there that you won't need for just a general overhaul. Typically, you just take everything apart, give it a good cleaning, replace a few o-rings and probably the diaphragms, and that's it. I'd go with the Bing kits:

https://www.bingcarburetor.com/cv-motorcycle.html
{old link was dead, updated link 11/30/21}

maybe kit #1 or 2...if you have the flat top carbs, you'll need different kits.

As for ethanol resistant floats, they used to offer some a while back but discontinued them. I dimly recall they're bringing them back, although the website doesn't mention them. But if they have something now, might be a good idea. I wouldn't go the independent float approach. Not really necessary, the settings are more fiddly, and you have to replace the float bowl which eliminates the overflow.

I just finished rebuilding a set of 32 mm and 40 mm Bing carbs and used the Bing kit that included a diaphragm, the float bowl and choke gaskets, the five o-rings you'll need and the two butterfly screws. As mentioned, I just took everything apart, gave everything a good cleaning and reassembled.

I found this video very helpful.

<iframe width="854" height="480" src="https://www.youtube.com/embed/F4_C5B-SjFo" frameborder="0" gesture="media" allow="encrypted-media" allowfullscreen></iframe>

Bing

Thanks, purchased what I need directly from Bing.

smt321 said:

Thanks, purchased what I need directly from Bing.

Click to expand...

Hope they didn't sell you those ethanol resistant floats. A friend who has them indicated they are difficult to set up properly and more prone to sticking or hanging up than the original. Expensive and unnecessary I think was the summary on that one...

Throttle Plate Screws

Beware : Grind off the exposed threads on the throttle plate screws before attempting to remove the screws. After installation, the exposed threads are peened so as to prevent them from backing out and being ingested into the cylinder. Failure to bring the threads off will prolly result in a ruin throttle plate axle. New ones are spendy. Be sure to re-peen the screws after rebuild; usually a two person task. I hear that some use Loc Tite instead. I have no experience doing that.

I hear that some use Loc Tite instead. I have no experience doing that.

Click to expand...

I do, not problems at all with Blue Loctite. DO NOT USE RED Loctite or you'll never take that carburetor apart again.

^^^ Not to be argumentative, but I think this is one of the few places that actually does call for red Loctite, at least if you don't plan to re-stake the threads. If one of these screws comes loose, we all know where it is going to go -- right into the combustion chamber, where it will wreak havoc.

Red Loctite will release with heat. These screws are easily accessible when the carburetor is off and there is no gasoline present. The heat can be applied with a soldering iron or a small torch.

smt321 said:

Hi all,

I'm gearing up to rebuild the carbs on my "new" R75/7 in January (my first). Bob's BMW sells this deluxe kit, which includes parts for a complete rebuild for both carbs: https://tinyurl.com/y8bl3crl

Has anybody here used this kit? Thoughts?

Bing offers a different float that they claim is more resistant to ethanol. Thoughts on this?

Any other advice you can provide would be very welcomed.

Thanks!

Click to expand...

Lots of stuff in there you likely won’t need and no sense having them sit on a shelf. Bob’s also sells a gasket and o ring kit that does both carbs for about $38. Add a couple of new diaphragms and you’re still way under $100. Once you get the carbs opened (one at a time please, so you have an example on the bench) you can assess the jets, needle jet and jet needle, and floats. Personally, I wouldn’t buy the alcohol-proof floats- they are fiddly to install and set and don’t add performance or reliability. Don’t forget to order new screws for the throttle plate as you’ll have to file off the protruding threads on the old ones before unscrewing them or you’ll destroy the threads in the $haft. The new screws can easily be lightly peeled once in place. I make sure the idle stop screw is unthreaded until it doesn’t touch the arm (you have to do that before installing/tightening the screws anyway) and have an assistant hold the carb in place over a 3/4” piece of steel rod chucked in a bench vise while I use a 3/8” diameter punch to peen the exposed threads just a bit. Spend some time looking over the carb section on Snowbum’s site at http://bmwmotorcycletech.info/bingcv.htm and take your time. Might also be wise to buy the Bing manual from Bing Agency, too—but you can buy your Bing parts from BMW at a lower cost.

Good luck, and ask more questions if you get stuck,

DG

There are two types of the ethanol resistant floats. the independent style that is more for the carbs used on aircraft engines and the ones that are a direct replacement for the stock floats the are in are carbs. I have replaced all my bikes with these a few years ago. Just need to ask for them when ordering form them.

Don

Thanks

Thanks for all of the good suggestions. I decided to not replace the floats, unless I get in there and see that I need to do so. I will replace with stock floats, if needed. Everything else has arrived from Bing. Thanks again!

Independent Float and Bowl

Lots of dis about the independent float and bowl kit. Yes, they were designed for motors in experimental aircraft, ultra light et al. I’ve used them for twenty years, no issues. They are alcohol proof, and maintain a more consistent float fuel level than hinged floats. When accelerating with hinged floats, the fuel in the bowl surges rearward, floats drop and admit more fuel, more than is desired. The engine then runs rich for a few seconds when a stable speed is reached. Times many many accel-events over the course of a tank of fuel, and it makes fuel economy go down. The IFB kit addresses this. YMMV. My $.0.02.

Missing from the Bob's kit are jet needles. Fuel rushing past them erodes them. Those and diaphragms are the two items mostly needing regular replacement.

Jets

lkchris said:

Missing from the Bob's kit are jet needles. Fuel rushing past them erodes them. Those and diaphragms are the two items mostly needing regular replacement.

Click to expand...

When you get varnish build up in jets reducing size of holes do you try to clean with any mechanical means, only use carb cleaner or replace?
Ultrasonic cleaning toss whole carb in or disassemble and remove rubber parts? Also what type of cleaning solution should one use

179212 said:

When you get varnish build up in jets reducing size of holes do you try to clean with any mechanical means, only use carb cleaner or replace?
Ultrasonic cleaning toss whole carb in or disassemble and remove rubber parts? Also what type of cleaning solution should one use

Click to expand...

Yes, carb cleaner, then magnifying glass or loupe to inspect small holes (ex. pilot jets) after air blowing them out. Avoid hard metal scrapers or wire (I avoid the wire jet cleaning tools, maybe copper, but rarely). Yes, replace when in doubt, but make sure you're not introducing jets out of spec. Ultrasonic: disassemble as much as possible, no rubber diaphragms, but thicker gaskets and o-rings OK for short periods (15 mins ±). Simple Green OK but can tarnish and stain carb bodies. Many swear by Yamalude carb dip, diluted with water, in their ultrasonics, and many even straight up vinegar. I think the ultrasonic does most of the work, heated solution next, and the solution itself is the least of the concerns.

I've found my ultrasonic cleaner isn't a miracle tool. I mainly use it to save time (it scrubs while I wrench) and for hard-to-reach passages, i.e. throughout the main carb body, and small jets. As important is an airgun: blow out all passageways after the cleaning. Find a cut-away diagram of your carb and use your fingers to block various inlets/outlets as you go, so the air blast re-routes through every hole and tunnel.

There's a thread on a vintage Kawisaki forum I follow where some guys tried a variety of ultrasonic methods and bath solutions until finding what worked best for them: https://www.kzrider.com/forum/21-tools/605673-ultrasonic-cleaner?start=20

I don't know if this is the OP's first time in rebuilding a carb (or bing carb), but there are a number of resources that may be useful when starting out. I liked rebuilding the carbs on my R60/6 so much that I did it several times before finally taking the bike to Re-Psycle BMW. Turns out there was something in the instructions that was misleading (to me) - I was omitting the rubber o-ring from the choke shut-off valve. I did discover that one can get about 12 miles to a set of plugs with the choke always on. The OP will not be dealing with a bing slide-type carb, but rather a CV type carb. Never-the-less, there are several things that one can do incorrectly.

For humour, and to help get one's courage up (and stock up on B-12 carb cleaner) it is recommended that you read the Carb Chronicles in the link below -
http://home.insightbb.com/~cdpumphr/the_carb_chronicles.htm

More serious and likely useful info can be found in the following links (not given in any order, just as collected) -
http://brook.reams.me/bmw-motorcyle...ld-project/bmw-r75-5-bing-carburetor-rebuild/
http://www.gunsmoke.com/motorcycling/r100gs/carb_rebuild/
https://www.youtube.com/watch?v=F4_C5B-SjFo (there are other associated videos shown on the right side of the screen)
http://www.ibmwr.org/r-tech/airheads/carb_rebuild.shtml
http://bmwmotorcycletech.info/bingcv.htm

Double thanks

wynk said:

Yes, carb cleaner, then magnifying glass or loupe to inspect small holes (ex. pilot jets) after air blowing them out. Avoid hard metal scrapers or wire (I avoid the wire jet cleaning tools, maybe copper, but rarely). Yes, replace when in doubt, but make sure you're not introducing jets out of spec. Ultrasonic: disassemble as much as possible, no rubber diaphragms, but thicker gaskets and o-rings OK for short periods (15 mins ±). Simple Green OK but can tarnish and stain carb bodies. Many swear by Yamalude carb dip, diluted with water, in their ultrasonics, and many even straight up vinegar. I think the ultrasonic does most of the work, heated solution next, and the solution itself is the least of the concerns.

I've found my ultrasonic cleaner isn't a miracle tool. I mainly use it to save time (it scrubs while I wrench) and for hard-to-reach passages, i.e. throughout the main carb body, and small jets. As important is an airgun: blow out all passageways after the cleaning. Find a cut-away diagram of your carb and use your fingers to block various inlets/outlets as you go, so the air blast re-routes through every hole and tunnel.

There's a thread on a vintage Kawisaki forum I follow where some guys tried a variety of ultrasonic methods and bath solutions until finding what worked best for them: https://www.kzrider.com/forum/21-tools/605673-ultrasonic-cleaner?start=20

Click to expand...

I have a 6 liter ultrasonic cleaner have a gallon of citric acid stuff mixes with water for ultrasonic cleaning think I will try the Yamaha stuff also have two 1980 KZ 440's so thanks also for the Kawasaki site

Bing service tip - do one carb at a time

I use the 40mm alcohol proof independent float kit on my road bike. Installed it myself, followed the instructions and it worked as advertised from the first mile. In fact I just OH'd a set of 32 IF's for a friend who uses them on his BMW airhead dirt bike. He says they are perfectly suited for off road work with the constantly changing attitudes one encounters. Service tip 1- keeping a carburetor clean from the beginning is feeding it clean fuel, clean air and using fuel additives that reduce or fight deposits. "Put a diesel engine up wet and a gas engine up dry". Drain the carbs and run them dry before storage and, drop the float bowls to see if there is any accumulated water in them occasionally when you are riding regularly. Service tip 2- At the moment, for less than the price of one new carburetor ($580.00) you can get both of yours rebuilt to new condition by mail order. And, #3 - the instructions are out there for you to read and follow with only so many steps and just basic tools. Kits and parts are available and individually inexpensive... Damaged 'throttle shaft' - $14.00. It is your turn to learn.

Late to the thread

Good evening all, I was reading through this thread as I was planning on rebuilding the carbs on my '85 R80RT. I clicked on the bing link on the first page of this thread and it is dead. Any other resources where to get rebuild kits for bing carburetors? Much appreciated.

I found the correct site! Keeping my fingers crossed for a first carburetor rebuild.

Worked for me -- try this https://www.bobsbmw.com/store/product/deluxe-carb-rebuild-kit-for-32mm-cv-type-1970-78