BMW R75/5 won't idle when cold, leaks gas out bowl.

Hey all,

I'm planning on pulling off my Bing carburetors for a little bit of an overhaul. Instead of pulling them off without any parts, I decided it may be a good idea to purchase the likely needed parts before starting.

The bike is brand new to me, and has 29k registered miles. I'm not sure when the last overhaul was, but I'm trying to resolve the following:

-Tough to start cold and won't idle until bike has been ridden about 5 minutes. Acceleration surges a bit while warming up. Idles decently after bike is warm.
-Choke seems to make no noticeable impact, and will actually make cold starting impossible--I've been starting it in 40-50 degree weather
-Left carb leaks out the bowl while on center stand if I leave the petcock valve open
-When coming off the accelerator, there is some popping in the exhaust

Parts I am considering procuring:

13 11 1 254 767 78 float needle 1
13 11 1 336 851 gasket kit 32mm & 40mm for 2 sides
13 11 1 254 766 63 float
13 11 1 254 768 62 float pivot pin

While I pull the Bing carbs off, are there any tips for things I should be looking for considering the symptoms above? Any other parts I should get or not get? After disassembling cleaning and replacing the gaskets and possibly float needle/float I will be also replacing the points/condenser/air,oil filter/and adjusting the valves, and attempt to sync the carbs as well.

Any help is appreciated as this is a brand new machine to me. Many thanks,

Nate

This is going to be a lot of information. I won't try to cover it all, I don't think I could, I'd forget something. But let's try to get you started.

#1...Always use the petcocks on your motorcycle. On that motorcycle. Anytime you turn off engine for more than 5 minutes (I felt I just had to have a time for you so it's 5 minutes) turn off both petcocks. They are there for a reason. The only way to make sure you are doing it right is to always do it the same way. You will get in the habit of turning them off and back on when leaving. (more on this if you like, research hydrolock, engine damage).

#2....Add to your parts list the diaphragms.

#3....Do one carburetor at a time. The other one, not taken apart will be your model. And most important is you don't want to mix the parts, especially the enrichners.

#4...There are several methods of cleaning carburetors. Soaking in Pine Sol (find thread in the garage forum for more info). Ultra-Sonic cleaners (if you don't already have one of these skip this method). Or Carburetor Cleaners. Also helpful is compressed air for blowing out the jets. So tell us how you plan to clean the carbs and we will tell you next about that method. (BTW my personal favorite is aerosol carb cleaners and compressed air) I also particularly do not like the Carb Cleaner in the one gallon can that soaks carbs. That stuff is junk.

#5....There are a series of numbers on the tag on the side of the carbs. You will have to report this info. Some of the earliest Bing carbs for the /5s had serious problems and hopefully somebody will tell you if you have those. It is something I only know about from hearing about it. My /6 comes after the early carb problem.

#6....What kind of condition are the four screws on the top of each carb holding the tops on? These are often a problem to remove and they can be replaced now unless they look particularly good and reusable. Try to loosen each one now and see if they will be a problem. If any of them are too tight don't fuss with it too much right now. You will need the new ones because some of them will be damaged when removed, maybe.

#7....Do not buy new OEM throttle return springs. If the old ones need replacing get the after market "Easy Pull" type.

#8....Get some Blue Locktight. This is labeled Medium Strength. A small tube from the auto parts super store or where ever you buy generic parts from. Hardware stores sometimes have this.

#9....You are going to need 3 cans of name brand spray carburetor cleaner. Do not get the "house" brand at the parts store. Get the more expensive one, it's cheaper in the long run. Brand names to look for are CRC and others, some like the one called B-12. (If you live in Kalifornica there won't let you have B-12 and some of the others too) This stuff is toxic. Use outside or in well ventilated area.

There will be more info coming from others. Don't pay a lot of attention to my use of numbers above. I just try to organize a little and the numbers are really arbitrary.

What year /5 bike?

Charlie

First off, welcome to the forum!

Also, I know it can be a pain, but pictures would help a lot. Besides, it appeases the inmates!

Since the bike runs fine when warmed up, I'm guessing the chokes aren't working properly. I'd hold off getting all those parts as they don't seem to relate to the problem at hand.

A little tutorial on Bing chokes is probably in order. (we need a FAQ for stuff like this).

Bings don't really have chokes - a choke is something that chokes the main venturi of a carburetor - which Bings don't have. Bings have an ENRICHENER circuit. What's that? It's like a small carburetor hanging off the side.

When you pull the choke cable, it's activating the enrichener.

Just to keep this simple, there are two main things that go wrong with these 'mini carburetors': air leak, plugged jet.

1. If there's an air leak, the enrichener won't have enough 'suck' to draw the fuel out of the float bowl. There are four screws holding the enrichener to the carburetor and they tend to loosen up. Just tightening them may not do the trick as the gasket tends to cave in around the air intake, causing a leak. Best to remove the four screws and take a look.

2. The enrichener draws its fuel from a corner of the float bowl. Down at the bottom of the well where the copper tube protrudes into, there's a small jet. Ensure it's open and free. Blow carb cleaner through it and make sure it sprays!

And finally, when starting with the choke, don't open the throttle. Only once the engine begins to catch you can open it a little. You'll get the feel of it.

I have no problem with Wirespokes approach.

You also have to check this leaking float bowl thing. The Gaskets can be bad, they are reusable but sometimes they get reused too many times. The floats can be out of adjustment or not floating because they are absorbing fuel. The float needles can be not working, most common cause of this seems to be a bit of debris stuck on the needle tip or seat area.

While you are cleaning the float bowl and small reservoir for the enrichner also clean the copper tube that hangs down from the main body into the float bowl. This is the enrichner pick up.

Place the floats in a bowl or cup with gas in it to see if they do float.

The metal tabs of the float that wrap around the pin can be too loose. Make them fit better. Bend with pliers.

The pins should be removable from the supports with a small punch but they should also stay in place. They should be just the right tightness in the supports.

Reports of problems with new float needles so don't expect new ones to be any better than the ones you have.

Wow. I came to the right place, and apparently with a support community like this, I bought the right bike! Thanks so much for the great advice already.

It's a 1971, and until I get the carbs off, here's a picture of the bike below to add interest to the thread:



That's my buddy's newer triumph in the back. I just put on a new seat cover I got off ebay for ~$55. Much better than duct tape.

disston, My approach to cleaning the carb originally was to disassemble and toss in my carb cleaner bucket, but I understand that to be a problem with these Bings. So I was going to basically use a aerosol carb cleaner and compressed air. I'll get some of those numbers off the Bing and post as well. Gotta get my workbench cleared and my garage in better shape now that I'm almost finished with a remodel of the house.

I just found out A&S cycles is here in Sacramento so it might be easier to pick up these parts once I disassemble than I thought. I'll post progress as I get it apart. I rebuilt the carb on my 1968 F150 recently, and although I don't entirely understand these devices, I had a system consisting of labeling of each part in order, and digital pictures between each steps... it seemed to work well, as it ran a million times better after reassembling!

Nate

Looks like you got a nice one Nate! I like it!

If you do pull the floats, there's something you need to know about the pins that hold them in. They're knurled on one end and need to come out that direction. Do not drag the knurling all through to the other side! They'll also be difficult to remove that way! I leave a finishing nail with the end ground flat, in the tool box to punch those things out.

So take a close look at each side and you'll be able to tell which side is knurled.

I install them with the knurling to the inside (the choke side - towards the transmission) because it would be easy removing them while the carbs are installed. That way I don't have to inspect each time I want to remove them - not that I ever do these days.

The seat cover looks good....did you get it from NW Classic Motorcycle Seat Covers?.....I've been thinking about recovering an old seat that I have.

Since your bike is a '71 there's a good chance that it still has the "Black Label" Bings. These are not to be confused with the later Black Labels; the early carb labels (or tags) are metal, while the later ones are plastic. If they are the Black Labels, don't waste your time or money. Find a later set-and the later the better. Any 32mm Bing used on a later BMW will work far better. All you'll have to do is install appropriate jetting.

Also, upgrade your choke control to a solid wire type. These also work much better than the ones originally installed.

Yup, that's the one. I'm pretty happy with it and installation instructions were useful. Big improvement over the original 40 year old one!

Here is a picture of mine 64/32/3 and 64/32/4:




Are you suggesting I should replace my carbs with a new set? Wasn't expecting to do that.... :|

I'd look for a used set, but yes-remove those and keep them as a souvenir. Keep an eye on Ebay and the IBWR Marketplace.

There's a 64/32/11 and 64/32/12 available at http://marketplace.ibmwr.org/ads/view/id/194365 -- is this a pretty much a standard consensus that these later carbs be replaced or should I give it a go and try an overhaul first?

Nate

I'd spring for the Bings on IBMWR. You've got a 40 year old bike, 2nd year of production and carb problems with known quirky early carbs. You'll save a lot of headaches by moving pre-emptively.

First thing I did when I began to plan my bike rehab was find something valuable I didn't need ... and sell it.

if your going to rebuild the carbs you have, I would just buy the appropriate rebuild kit from bmw, comes with all the o-rings and gaskets your going to need.

I'd listen to what bmwrench has to say - he's been professionally working on these things his whole life. If he told me I'd be miles ahead replacing the carbs, that's what I'd do.

In the late 70s there was a flat top version of the 32mm Bings and I'd stay away from them for two reasons - replacing the diaphrams can be trouble and they don't look right on your bike.

Sometime around the early 80s they were modified with a top retained by just two screws, not the four on yours. But they'll work just fine.

I agree that you should replace those carbs and NOT try to rebuild them. Don't throw them away. They go with the bike when/if you ever sell it. It is a known issue, the earliest Bing 32mm carbs used on your vintage BMW were not right. There is apparently no easy fix. I don't have those and have not dealt with this problem but it's one of those things that if you are around long enough you will hear about it. You might find the "story" or somebody here might tell it again but the bottom line is get the later carbs, the ones on IBMWR look good, and jet them for your bike.

Or if you want to spend more money we will tell you about Mikuni Carbs. They are liked by some. The are not cheap. But by the time you get another set of Bings and rebuild them it's not going to be a lot more than the Mikuni's. The Japanese carbs are about $500 with cables.

Some of the parts from the old carbs might fit the new carbs but I don't even know if that is so. Along with the new carbs if you have the flexible choke pull cables convert them to the solid cables.

You might as well start with the book from Bing. It costs $11 (includes shipping) Here is the address for the book. You can also get other things there but when you buy parts for any of these carbs, the parts usually cost less at a BMW dealer.

http://www.bingcarburetor.com/

Charlie

Later carbs would be a plus but I don't think anyone has mentioned that all airheads won't idle when they are cold if the are set up to idle normally when they are good and hot. The perfect airhead will also pop on decel depending on how the air mixture screw is adjusted. A perfectly setup airhead will not run right with no choke while it is cold until it warms up. That is what chokes are for. If your carbs are set up to run well with a cold engine, they are power and MPG robbing too rich after it gets warmed up. Your carbs can be set up to run well with an engine temp range that it has one tenth of one percent of its life or they can be set up to run well with an engine temp that it has 99.9% of the time. The latter is the smart way to go. That's why the carbs have chokes to begin with. Just a friendly reminder from ol' supershaft!

It's true that the bike won't run the best while on choke, but it can run well, and smooth. There's no need to have it idling perfectly since we're talking five minutes till it's off - and it really shouldn't be idling very long anyway - just long enough to be down the road. Some guys constantly blip the throttle or hold the RPMs up during warmup, but with cold oil not flowing so well, I prefer to keep RPMs low as possible at first.

But I don't think that's the problem here - it's just not starting.

At the end of the day, it sounds like I might have a problem with the enrichener (air leak or plugged jet) and the float/float needle might also need to be adjusted. Otherwise the bike does run good. I'll look at this as a learning experience and see if I can resolve on my current 64/32/3 /4 --- if I fail, well, I'll look at a later model pair and start again.... any money I waste on parts for these older carbs I'll chalk up as a tuition fee in the school of hard knocks.