Carb Work R69S

[schrader7032]

Last time out, I felt that the low end performance was a bit rough, but seemed to run somewhat OK at higher RPMs. Nonetheless, I figured time to give the carbs a once over. They were both fairly clean and I used carb cleaner to ensure that all the passages were open. But I discovered that the main jet holder on the right carb had migrated up into the carb throat. It's like what Duane shows here on this picture:

https://w6rec.com/duane/bmw/carb/bad.JPG

Not a great picture, but I could see the serrations of the holder. So, I found a socket that fit over the holder and with a ratchet extension proceeded to tap the holder into place. I suspect that was causing my issues. I think that the jet stack screws into the holder. So the raised holder prevented the carb slide from setting down as well as pulled the entire jet stack up and maybe created issues with fuel flow.

One thing that I was unable to get to the cover off to the sidecar chamber as I understand it from Duane's site. See the large cover on the right in this picture:

https://w6rec.com/duane/bmw/carb/new2.JPG

I had a piece of metal that fit the slot well and I grabbed it with my visegrips. But it was stubborn and I very nearly drew blood!! In the past, when I did get the cover off, I don't remember ever seeing gas in there. On a solo bike, gravity and fuel flow is straight up-and-down. But on a sidecar bike, fuel will be pushed to the side in the turns and apparently it can starve the main jet...I guess that is the purpose of these chambers. I'm not going to sweat it at this point...hopefully that won't come back to haunt me!!

I'll have to keep an eye on this. I've had the bike for 10K miles and over 15 years, so maybe it's a slow mover. But if it does, I'll probably consider using some wicking Loctite.

[jnclem]

I just had the same problem on the right side on a 1958 R60. It seems those are coming loose more often as the bikes age. I did what you did for now, and just tapped it down. That completely solved the issue, but I expect it to reoccur sometime when the carb is good and hot. At that point, if not before, I plan to warm the carb up with a heat gun and pull that mount all the way out. I’m going to clean
it well inside and out, and reinstall it with some loctite high temperature sleeve adhesive. I’m hoping that will be a permanent solution.

[schrader7032]

I forgot that this issue with the jet mount was covered before:

viewtopic.php?f=7&t=17446

This will help keep things together.

[Flx48]

"On a solo bike, gravity and fuel flow is straight up-and-down. But on a sidecar bike, fuel will be pushed to the side in the turns and apparently it can starve the main jet...I guess that is the purpose of these chambers."

Hi Kurt-
That might be expressed by saying that gravity, as well as centripetal and centrifugal forces, are all in play equally for both solo and sidecar bikes as they round a curve.
In either case the fuel in both the carb's float and s/c bowls would be thrown to the outside of the corner by centrifugal force, the difference is the solo bike leans and the sidecar bike does not.
So when the solo bike leans, the lean angle makes the fuel level's angle seem flat and normal from the bowl's perspective, while the non-leaning sidecar bike will have the fuel climbing the up the side of the bowl towards the outside of the corner, since there's no lean.
So by leaning, the solo bike has moved the center of gravity from under directly under the rider, over towards the inside of the corner, perhaps under the rider's knee, hip or elbow, depending on the speed.
When rounding a curve that same lean is producing a centripetal force to equalize/neutralize the curve's centrifugal force.
Centrifugal force pulls the bike to the outside of the corner, centripetal force pulls it in an equal amount. (otherwise we fall)
Conversely, the sidecar bike has no lean, and depends on the third wheel to create some centripedal force, but cannot hope to create as much as the leaning solo bike, because the sidecar center of gravity will swing to the outside of the corner, and so not be able to create a countering centripetal force.
The sidecar bike must simply negotiate the curve at a gentler pace than the solo bike.
Sidecar racers compensate with great wide tires for maximum adhesion/friction, and a pancake profile to create the lowest possible center of gravity.

In the carburetor , the sidecar bowl is located on the opposite side of the main jet from the float bowl; so one bowl, or the other, will be feeding the jet whenever the cornering slosh occurs.
The sidecar bowl is an empty chamber, (except when the carb is fed gas) with two orifices into the main jet chamber, that match those of the float bowl to the main jet chamber.
The only problem one may encounter by not inspecting it is if it contains fuel residue that has crystalized or shellacked the surfaces, which may at some point break loose and travel into the jet to create havoc.
If you're having to use ethanol fuel this may be more of an issue at some point.
Maybe soak the threads?

Yes, I'm inside reading the forum today instead of out side riding, it's just to cold for me today...

Best-
George

[schrader7032]

George -

I'll have a check next time. I wish BMW had used a hex cap instead of that slotted thin cap. I really struggled to get the air horns back on the carb. I know it's a fine dance with looseness in the carb attach and position of the horns...got to get things just right to slip it by and into position.

I had the bike out this morning after the carb overhaul. She started right off and ran well, so it looks like things were corrected with that jet holder repositioning.

[Flx48]

That's great success, Kurt-
I've not had to do that task.
Yet.
And maybe try the ole squirt of your favorite solvent thing every day for a week or two on the s/c screw cap, see what happens?
Best-
George