Bing type 54/84 experiment

[typ181r90]

I don't know if anyone cares about this but I haven't heard of anyone actually doing it so I figured I'd post my plans and results. Maybe another round slide alternative to Mikunis.

Here's the scoop

Currently my R90/6 has the Bing type 64 CV carburetors in their stock configuration with the exception of drilled holes into the airbox to allow for COOLER air to reach the carbs (not more air as it seems like people confuse it for). It's actually running perfectly, but it seems like once I get everything perfect I have to start messing with things. Engine is stock with the exception of SJ light aluminum pushrods and this February I'll be putting in 9.5:1 pistons with freshly bored/honed cylinders, lightening the flywheel, and getting the heads tapped for dual plugging - want to have that option but I'll leave them plugged until I save up for the the rest of the equipment. I got a fresh valve job last winter and wish I had that done at the time but no biggie.

With this work being done I thought of switching my Bings for Mikuni round slide carburetors or Dell'Ortos (if I could find them for the right price) running velocity stacks. I don't personally know anyone in my area who did the conversion so I've only heard of the benefits (easier starting, snappier response) but as I don't have personal experience I don't know how dramatic the difference would be. Not wanting to invest a lot of money I found instead two Bing type 84 carburetors in 32mm bore (like the type 64) for $38 and $56, I wound up buying a 3rd, never type just for extra parts. I ideally wanted a Bing type 54 in 34mm bore, but couldn't come across a pair in that size.

With the Bing 84 you're essentially getting a Mikuni VM32, which rocky point sells for around $460 for the kit. I own the Bing carburetor manual for BMWs which I haven't had much use for until this point. As the type 84 in addition to the 64/53/54/55 are all included in it it gave me a lot of information on parts numbers and jetting from which I was able to determine:

- it uses the same float bowl as the early type 53 carburetors and gaskets
- the float bowl depth is the same as the type 64, except for the ones which I'll be using that have a main jet reservoir
- it shares the same choke piston as the type 53
- the type 53 throttle cables work with it (got them on sale from eurotech, $28)
- Main jets and needle jets are the same as the ones in the type 64, the jet stock diameter/thread/and length are the same as the type 64 but I don't know if the mechanical pump in the type 53 will work, but I doubt it
- pilot jets are the same
- the floats match the ones in the type 64, I'll actually be using my ethanol resistant ones that I'm currently using for this experiment
- the atomizer is pressed in on the type 84 and this is part of the equation I can't really account for

The beauty of all of this is that all the parts can be bought from BMW and in my case a dealer is only 5 miles away. Additionally, the manuals for the carb can all be found on Bing's German website www.bingpower.de

the carb broken down, sorry for the crap cell phone pics

the new type (tabbed choke adjuster and metal clamp style) in comparison with the older type (a simple pull and lock choke and additional float tickler) intended to use with a rubber hose mount like the stock ones. I'll be using 2 of the older type and keep the newer one for parts.

Note the old one without the main jet reservoir in the float bowl, I'll be using the reservoir type on both my carbs

Finally here's a pic of the velocity stacks I ordered. I couldn't find a whole lot for the OD I needed and the ones I could find were threaded. These popped up on ebay which were designed apparently for the Type 84/54 carbs and are coming from Argentina. I like that they have a foam filter element on top of the screen, but I'm dubious as to how they'll function, may just continue to go with the stock airbox set-up. The dimensions of the stacks are quite large and should work fairly well, 108mm length x 94mm diameter

I know I'm going to have to experiment with jetting and currently have 145, 150, 160, and 170 main jets, 2.68, 2.7, 2.72, and 2.73 needle jets, and 240 old style needles (may need to get some different ones if I can't adjust the mix enough with using the notches)

Here's a breakdown of the cost:
Carbs - $94
Cables - $28
Rebuild kit - $25 (only needed one)
Misc. jets - apx. $40
New choke pistons - $10
-------------------------
$197

The velocity stacks were $109 with shipping but I'm not going to include those with the carbs because I'd be buying them anyway with Mikunis.

If I can get these carbs working pretty well, that's a significant price difference to the Mikuni kits and Dell'ortos (which I can't find cheap anywhere) and you'll have period correct, German built carbs. Furthermore if they don't work I can always reattach my perfectly working CV carbs and I should be able to make back most of the carb money by selling them, now fully rebuilt.

Still waiting for the velocity stacks to arrive, maybe by the end of the month, and will update with my progress.

 

[helmut_head]

Why would you lighten up the flywheel? The weight you remove will all be inertia for damping torque pulses. You'll never see a measureable difference in performance.

 

[typ181r90]

More immediate acceleration, less required power to turn the engine, snowbum notes the drawbacks which as you said are more vibration http://bmwscotter.org/topics/common_modifications/lightened_flywheel.txt

It's been a topic beat to death on this board and others and I discussed it with an airhead guru (who will actually be doing the lightening and balancing). I'm comfortable with the sacrifice as I want maximum performance while still being a "streetable" bike. It was because of this reason that I won't be using my 336 cam in this project as I was talked out of it by the same guy

 

[1961BMWR69S]

just a idea for you if your trying to make a faster bike, i took a stock 78 r100/7 and made a cafe bike out of it. engine work- what i did was i put a 336 cam, stock 32mm bing but did jet the carb, put k&n filter right on the carbs, get hoska muffler and pull the baffles out that will make a huge difference it will be load . In 1gear and 2 gear the front wheel would come off the ground when i get on it hard. the bike is supper fast.

 

[helmut_head]

Yah, I see what you are saying and respect what you are doing. I tend agree with 46211 that lower exhaust back pressure, cams, porting, fueling, and reduced intake restriction would be a wiser choice for performance. You'll never be able to tell the difference with a lightened flywheel alone-seriously. Heck the BMW flywheel is pretty light already. You'll be hearing alot of neutral spline rattle.

Good luck with it though.

 

[typ181r90]

Well it'll be lightened from about 12lbs to a little over 6lbs so that's a decent cut in weight. I forgot to mention that the exhaust back pressure is already reduced as I'm running baffleless dunstall replicas. Picture is outdated, but the muffler is the same

 

[LOSTBOY]

Yah, I see what you are saying and respect what you are doing. I tend agree with 46211 that lower exhaust back pressure, cams, porting, fueling, and reduced intake restriction would be a wiser choice for performance. You'll never be able to tell the difference with a lightened flywheel alone-seriously. Heck the BMW flywheel is pretty light already. You'll be hearing alot of neutral spline rattle.

Good luck with it though.

Are you confusing the /6 flywheel with the '81-'95?

 

[LOSTBOY]

Well it'll be lightened from about 12lbs to a little over 6lbs so that's a decent cut in weight. I forgot to mention that the exhaust back pressure is already reduced as I'm running baffleless dunstall replicas. Picture is outdated, but the muffler is the same

The /6 fllywheel weighs a little over 7lbs-unless you're including the clutch assembly.

 

[typ181r90]

The /6 fllywheel weighs a little over 7lbs-unless you're including the clutch assembly.

I have the early version like the /5 with the 10mm bolts, I have a spare one in case I want to bring the bike back to stock one day and my scale shows close to 10lbs, my scale could be off though as it's a cheap one from IKEA... still less than 12 though

this thread is about the carbs though

 

[1961BMWR69S]

Great looking bike Typ181R90.. Are u trying to make the faster off the line.. About your carb idea, try it. You still have the stock ones. The slide carb will work. I installed a set of mikuni 32mm on a r100 bike for a buddy of mine. Bike had 32mm bings. It did make a little diffenece when u roll on the throttle. The big problem I had was jetting the carbs right. I wish I could remember the size jet. What every jet it had the bike ran lean. He sold the bike after riding it about 25,000miles and never had a problem.........

 

[helmut_head]

Thinking 1983.

I like that bike, very nice. I'd go after the intakes next.

 

[lkchris]

This proposal installs carbs BMW abandoned for the better CV versions. Nothing about the old designs makes them "performance" carbs.

 

[typ181r90]

This proposal installs carbs BMW abandoned for the better CV versions. Nothing about the old designs makes them "performance" carbs.

Not necessarily. I agree you won't find the all around performance that a cv Carb will give you and probably the reason BMW used them, but you'd be hard pressed to find an ahrma bike running cvs instead of mikuni VM carbs. BMW also used the 27mm type 53 into the /7s for the r60 which obviously is newer than my early /6.

Like I said in the beginning, there's nothing wrong with my cv carbs, I just felt like experimenting with a vm32 type carb running velocity stacks (which although I'm no physicist would not work very well with vacuum carbs). I do expect to.get a more.immediate throttle response, perhaps at the cost of performance in the midrange, but we'll see. Again, if I don't like them I'll be going back to stock.

The whole point of this thread is to try something new that may possibly present someone already looking to switch to mikunis or dell'ortos with a cheaper, more accessible option. I know the moa seems to generally be anti-modification hearing all the contempt for German customs in the threads concerning the BMW Motorcycle Magazine (which I happen to love), but maybe that's because I'm 27 and well below the average age for the club.

If it works well, I'll post my results and jetting configuration so someone else out there can Just bolt one on like a pre-jetted rocky point mikuni, if it doesn't you can laugh at me when I put my perfect running type 64s back on. Don't forget though that the RO scuderia BMW r1200 racer gained immediate performance just by putting on a Bing type 55 gold.cup Carb and dumping the stock "superior" fuel injection

 

[helmut_head]

Now that we got that flywheel thing outta the way, my money is on you, Typ181R90.

 

[8ninety8]

Go for it

Anything laying around the shop that looks like it might kill a little of the bleak winter, play around with it. You've always got all the pieces to put it all back to where it was. If it's an extra bike, even a better deal.

As for the velo stacks, stock plastic intake runners probably help in the regular day to day riding smooth out the flow in, like the header going out. I run Dels, and they're right now throttle response stock settings, 336, punched out Zuenas, DP'd, whatever, gotta have some fun. 3 sense only.

 

[mymindsok]

BMW MOA guys argue about the oddest things...!

Lightening the flywheels has been an accepted performance mod at least since the 60's and I've done it to every Airhead I've owned, mostly because of the improved shifting, though the bikes do wind up a little faster.

IMO, the best thing you could do would be to get rid on the Flywheel entirely by installing a late model clutch and transmission. Sure the bike vibrates a little more but the newer clutch is an easy 300% improvement!

I won't comment about the carbs except to say that I found a set of original Dells off of an R90S on Ebay for $200, so at least I'll be working with a known quantity when I put em on my R100.

I'll be checking back to see how your project goes.

Good luck!

 

[8ninety8]

Light assembly on /6s

Will a light clutch assembly fit an early /6 with the 10mm flywheel bolts? And the trans spine/clutch plate fit? Have always thought it wouldn't bolt up, but don't know for sure. The two times I removed mine from '74 900, couldn't believe what a piece of iron was laying on the bench, even when lightened, but put it back in.

 

[lkchris]

No, the late-version clutch requires different input shaft on transmission.

 

[happy wanderer]

Lightened flywheel?
There's this guy.. called Reg Pridmore?
His flywheel spun pretty good.

 

[8ninety8]

Works better than the old one

Here's what a machinist did to mine a long time ago, had to make new dimples which I repainted last winter. Apparently the more weight removed from the edge, the greater effect, as the leverage is greater the further the distance from the center. Would rather have the factory light basket. Didn't want to put too many holes, may crack?, some look like swiss cheese.