88 R100RT stumbling at 2K rpm

[3moskvichi]

I just took my 88 R100RT out of an 11 year hibernation. Mostly it's ok, since I had completely drained the gas from the tank and carbs and put fresh fluids all around.
However, it now has what I call a "stumble" as I throttle up at around 2K rpm. I can't tell if one or both cylinders are "missing" at that rpm, but as soon as it's past 2k, it's good. At around 60mph, though it seems to be sort of starving for fuel, since a it takes more than the usual throttle movement to nudge it faster. It'll go faster easily enough - it just doesn't have the smoothness I remember. Plus, mpg is down too - to about 39 - with really mild riding, whereas I used to get 45 while really wringing its neck.

Anybody care to comment on whether this might be a carb issue, and how to smooth out the throttle response?

[04R1150RS]

carbs might be gummed up w/ the old vintage gas that's been fermenting for 11 years, i.e. glogged jets and stuff. That stuff gets really nasty over time.

[tghsmith]

check the diaphrams in the carbs.... clean the carbs...

[DennisDarrow]

A couple of quick thoughts:

First..........welcome aboard

The quality of gas has detiorated in the last 11 years; thereby worse mileage.

In 11 years perhaps your carb diaghrams have dried out and one has a crack. Perhaps your O rings on the jets have also gone a bit south. It would be worthwhile to pull the jets and diaghrams, clean, inspect and replace and then see. What you are describing is pretty classic for these problems.............Dennis

[AnnapolisAirhead]

check the diaphrams in the carbs.... clean the carbs...

Welcome aboard!

+1 on the diaphrams, that probably the starvation at 60mph you are referring to, in my opinion. Could also be just general stickiness all around. Mine was hibernating for 8 years. Probably not a bad idea to get new o-rings, diaphram, needle, floats and atomizer then a good cleansing. The enricher/choke is probably somewhat suspect too and worth new o-rings.

The stumbling could at 2k could also be as simple as throttle cable adjustment (one being out of sync with the other). As you ramp up speed, you won't notice as much until up around 70mph. At least that's what I experienced.

Still, after 11 years, the old gal deserves a good carb cleaning/rebuild, IMO. :-)

[3moskvichi]

Thanks for the comments - sounds like a good thorough carb overhaul is in order after so long in storage. Over the years I seem to recall having read of rebuild kits for the Bing carbs - any recommendations on sources, and are they worth it, or should I be looking to buy seals and diaphrams individually?

[88bmwJeff]

Any BMW dealer should have the parts or call the Bing Agency. You should also get the Bing Manual.

http://www.bingcarburetor.com/

[AnnapolisAirhead]

Thanks for the comments - sounds like a good thorough carb overhaul is in order after so long in storage. Over the years I seem to recall having read of rebuild kits for the Bing carbs - any recommendations on sources, and are they worth it, or should I be looking to buy seals and diaphrams individually?

If it were me, I'd buy the kits (most BMW dealers have them). Maxbmw.com has a microfiche like a lot of places, where you can select your bike (model and year) and pretty much source at least the part numbers for anything. They sell most of the parts, but it pays to sometimes shop around (Chicago BMW has good prices http://www.chicagobmwmotorcycle.com/store/ just plug the part number in or call them).

Also, here's another link to kits: http://eubmw.com/Carb.html or Capital Cycle/Euromotorsports: http://www.euromotoparts.com/Merchant/merchant.mv?Screen=CTGY&Store_Code=1&Category_Code=120

Here's a list of parts I'd recommend (ask me how I know, 7 times...finally got it right).

diaphrams
Main jet needles
Main Jet Atomizer (the brass part with the holes in the side, receives the needle)
Floats
Float needle
Float bowl gasket
Enricher/Choke housing gasket
O-ring set (for Main Jet, Idle Mixture screw, Choke assbly).

Unless your butterfly valves/flaps are gunked up, I'd just clean that with carb cleaner and NOT disassemble it. Don't use brake cleaner to clean anything with an o-ring (it'll compromise the rubber integrity, sooner or later).

Make sure you align the diaphram in the carb properly--the diaphram has a little flap and the carb housing has an indentation to receive it.

Lastly, do one carb at a time because some of the part are 'handed'.

Send me a private message if I can help or need to call. I love these carbs. :dance

ps. Yes, exactly what 88bmwJeff suggested. Get the Bing manual! I wish I did before I started. As you disassemble the carbs, write down the numbers on the various brass parts and the carb itself. If you have to call Bing, that's all they'll need.

[88bmwJeff]

I have one other suggestion to add to AnnapolisAirhead's list. If you are going to be replacing the jet needles, then you should also get the needle jet. I've had good luck cleaning the atomizer, but if they are really gummed up, they could be a PITA to clean.

If you've never cleaned the carbs before, or if it's been a while, the two screws that hold on the butterfly are peened. If you decide to remove them, you MUST file them down to shaft. Otherwise you will be replacing the throttle shafts as well.

As far as mileage goes, I also have an 88 R100RT. I've followed MANY a thread on mileage. It seems that most later airheads (R100's) with the 32mm carbs tend to get in the mid 30's for fuel economy. I can get in the low 40's if I'm doing 100% freeway riding

[AnnapolisAirhead]

I'm getting low 40's and once in a blue moon (when I am being consistent and reasonable) I can scrape 45-46. '83 R100T, 40mm Bings and dual plugged.

I have made the mixutre slightly richer as a test to get rid of popping on normal decel and that seems to have dropped me back into the high 30's. I commute mostly on highways (but that doesn't always mean consistent speed...it IS the DC beltway afterall).

[Isamemon]

first I agree with overhaul the carbs
another great "manual" is the On magazine back issue March 2003
check and you might still be able to order at this forum ounder back issues.
for me , it was one of my best learning tools the first time I did the carbs on a old BMW
2nd
if you shop around, you can save money buying some parts from bing and some through the bmw dealer
3rd
a friend of mine pulled his kawasaki out of storage, yes a different bike
he "cleaned" the carbs but had nearly the same symptoms, rough running, and a dead spot about 3k. smoothe at speed and under load with the exception of the dead spot. in talking, he had run a new tank of gas but also some carb cleaner mix. Might have been a co-incidink, but we drained the tank again, drained the carbs put in fresh gas with out an additive, and in about 5 miles his dead spot went away. could have been the carb cleaner, or just a co-incidink

but agian I would go through the carbs, soaking them overnight in a dip tank ( after they have been dissasembled)

[kbasa]

Yup.

Carbs are full of crud. I'd guess that main jet has got goo in it and as the bike transfers over from the idle jet to the main jet there's enough junk in the main jet to prevent it from working well when it's partially open.

If you're going to take it apart, you might as well rebuild it.

A couple gotchas:

- Jeff rightly pointed out the issues with the throttle plates. They only go in one way, due to a very slight bevel on the edge of the plates. Mark their orientation with a sharpie or some blue tape prior to removing them.

- Don't get the enrichener bits mixed up. They have an orientation and are easy to mix up from side to side or to get in backwards. I replaced the stock gaskets with some nifty neoprene ones I found online somewhere.

- Installing the rubber Orings on the little parts can be a bitch. I use a bit of axle grease to ease installation, along with a small screwdriver as a wedge. Others may have other methods.

- I use a muffin pan to keep all the bits organized. As I remove a part, I put it in the tin. I've numbered the holes in the pan so I know which parts came off first, second, etc. (Do not use your wife's pans, DAMHIK, buy your own. Better solution, buy her some really nice ones and ask for her old ones)

Good luck!

[AnnapolisAirhead]

Getting the o-rings over the threads can sometimes damage the o-ring and can be tough (as Kbasa says). I've seen grease used and have used teflon tape and electronics heat shrink tubing with grease to cover the threads.

Another pain can be gettign the carb tops off. Due to dissimilar metals of the screws and the carbs top (and general crud), its real easy to strip the phillips head. I ended up using an impact driver, braced the bottom of the carb top wing on a wooden bench and gently (repeat GENTLY) tapped a couple times until it moved. Just be carefull or else :banghead

The rest I unscrewed with a properly fitting screwdriver. When you put the carb top back on, I used a tiny bit of anti-seize on the screws.