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ocallahan7436
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Hi folks. I need some guidance on setting up the carburetor on my R62. I have just completed an overhaul of the motor. The motor starts easily,but, the gas mixture is very rich,resulting in lots of black smoke and very black plugs. The jets have no markings,so, I cannot identify their size. The carb float also needs to be set correctly. Any guidance would be appreciated.

Darryl.Richman
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Manual?

When you're getting black smoke, do you have the air lever open all the way? It acts as a choke and richens the mixture. On my R52, I find that I only use the air lever when starting, and to get a really slow idle.

Do you have the R52/R62 Owners Manual? It has a detailed description for setting up the carb.

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ocallahan7436
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R62 carb settings.

Hi Darryl. I am pretty certain that the air valve is full open. Like you, I only close it for starting. The manual gives guidance on setting the slow running which is ok on my machine. There is an adjustment screw on the carb, close to the manifold. I presume that it is an air adjustment. I set it to the fastest running position, and then backed it off a little.
I will be in Spain for the next week. When I get back I will take another look at the problem. In the meantime, I would welcome any firther advice.

Darryl.Richman
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Tim, I am green with envy. I

Tim, I am green with envy. I was fortunate enough to spend 4 weeks riding around Spain in 2002, and I want to go back. What a beautiful country with wonderful people.

The screw you're talking about is the idle air screw, and it sounds like you're adjusting it correctly. But there's a throttle stop screw, which controls the idle mixture. It's located on the right side of the carb. There's a lock nut on top and an odd looking screw head underneath. As this screw is turned clockwise, it raises the throttle slide stop position.

If you haven't noticed it before, the idle "circuit" on these carbs is pretty strange. The idle jet projects up into the carb throat. When the throttle slide is less than about half open, it covers the idle jet and so it doesn't participate in the carburetion. (Above about half way, the small contribution it makes is not noticeable.)

When the throttle slide is all the way down, there's a horizontal hole that runs through the throttle slide, and lines up with the tip of the idle jet. At this point, the idle jet contributes its fuel to the carburetion and allows the motor to run.

The throttle stop screw seems to do two things: it adjusts the alignment of the hole with the idle jet, and it also controls how much air goes under the throttle slide, and therefore, how much the main jet contributes to the idle.

To set up the carb, you should first get the engine thoroughly warm. Then loosen the adjusters for both air and throttle cables so that there's some play at the levers.

Now, adjust the stop screw for the slowest consistent running position, and then adjust the idle air screw to fine tune it. It may take a couple iterations to zero in on the best running condition.

Once you have the idle set up, adjust both cable adjusters so that the cables have a very slight amount of free play, 1-2mm. You need the full swing of the levers to open and close the slides, so they do need to be adjusted properly.

If you can achieve this and your bike is still running very rich, your main jet is probably suspect. The owners manual says that the jets are supposed to be stamped with their size, but it doesn't say what that size is.

My motor also runs somewhat rich. In my case, the air and throttle cables appear to be the wrong lengths, and so are at the ends of their adjustment ranges on top of the carb; the throttle is slightly short and the air is slightly long. I haven't fixed this because, at least on my bike, the cables appear to be permanently attached to each slide. I believe that the throttle slide is being held slight up off the stop screw and that the air slide cannot be pulled completely out of the carb throat. In both cases, I think the distances involved are very small, maybe 1~2mm. (For example, the throttle stop screw does nothing on my bike until it is most of the way in.)

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ocallahan7436
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R62 carb settings.

Hi Darryl. Greetings from Spain. I agree with your comments regarding Spain. It has everything for the motorcyclist, great weather,great roads with no traffic and great scenery. The food and people are an added bonus.
Thank you for your posting on the carb settings. It is most helpful. Do you have any guidance on the float setting? At present, I have set it so that the fuel level is just below the tip of the main jet.
Dreher in Germany has a selection of main jets. I will buy a few different sizes and experiment with them, to get the mixture right.

Darryl.Richman
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I hope you'll report back

I hope you'll report back your experiences. There's so little information about these early bikes available, every tidbit helps!

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sblaylock
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Darryl,Great explanation on

Darryl,

Great explanation on how to setup the carb. I used this method and it worked beautifully. My main jet is stamped with a 90, but the idle jet has nothing on it. Is the idle jet suppose to be longer then the main jet? My idle jet is longer and actually pushes the slide up a bit when the throttle stop screw is backed all the way off. Surprisingly, the tip of the idle jet is perfect without setting the throttle stop i.e. with the idle jet pushed as far into the slide as possible, the tip is just showing in the hole through the slide. I adjusted the throttle stop so the slide is not resting on the jet, then adjusted the idle air screw as you mentioned. The bike idles far better than it did when I got it.

Thanks for writing this up. It was very helpful,
Scott.

Darryl.Richman
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I think 90 is the right main

I think 90 is the right main jet size for the R62; and 80 for the R52. At least, that's what it says in the parts book. Because I will be running my bike at high altitudes over the Rockies during the Cannonball this September, I plan to get a couple extra main jets and try soldering and redrilling them to slightly smaller specs, to see if I can lean out the carburetion safely. I know that my other slide carb bikes don't like being above about 7000 feet, when they are jetted and set at 650 feet here in Santa Cruz.

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Ian R11
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My carb is in bits at the

My carb is in bits at the moment. If it helps my observations are....
My main jet is stamped 85. My idle jet is longer and also not stamped with a size. It does not push the slide up at all, and the end of the jet is visible in the small hole in the slide. The top of the jet is a little over half way up the hole viewed from manifold side, without the slide adjusting screw holding the slide.

sblaylock
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Thanks Ian. My slide is not

Thanks Ian.

My slide is not original so I'm guessing the hole larger bore wasn't drilled deep enough and it's bottoming out on the shoulder of the idle jet. Not a big deal, as it seems to be running pretty well and, as I mentioned earlier, I've adjusted the slide height screw to lift it just off the jet.

Scott.

sblaylock
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I need some guidance on how

I need some guidance on how to fix a mid-throttle issue. The bike idles really well and with the throttle opened up it runs smooth, but driving around at 50 to 60km (30 to 40mph) it is missing badly. My guess is it's in the transition between the idle jet and the main jet.

Here's a link to some photos of my carb: R62 Carb Smugmug has been misbehaving this morning, so I'm not sure if you will be able to see the photos.

As you can see the throttle slide is a homebuilt by someone in the bike's past, so I'm thinking the issue is there.

I may look at adding a small washer under the jet to see if raising one or the other makes a difference.

Any suggestions would be appreciated,
Scott.

Darryl.Richman
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The BMW carb is an

The BMW carb is an interesting thing, something I'm not at all sure about. The idle jet should sit directly in the lateral hole in the throttle slide, when the slide is closed. Even at idle, this should create significant vacuum and suck as much gas out of the idle jet as it will flow.

When the throttle slide is raised, the hole will misalign with the idle jet, which will feel less and less vacuum and so flow (and atomize) less gas. There will probably be significant turbulence in the well created by the hole in the slide that the idle jet fits into, and so even less vacuum effect.

Meanwhile, the airflow is now passing under the slide, pulling gas from the main jet. That narrow, semicircular cut in the bottom of the slide is supposed to continue to create significant vacuum at low engine speeds, but once the slide lifts up above the bottom of the intake bore, the full width of the bore will provide a larger opening, lessening the vacuum in any one spot. Hopefully at this point, thought, the engine will be running faster and will be sucking much more air through.

Unlike slide carbs with tapered needles, there are no differing needle tapers or needle height positions to allow tuning the carb -- pretty much, it is what it is. BMW supplied 4 different main jets: 80, 85, 90 and 95; your R62 should have come with a 90, and the 95 was considered to be a "sport" jet.

It might be that you've got the idle air screw open too much, and it creates a lean condition when the slide is just barely open.

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Ian R11
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I have managed to see the

I have managed to see the photo's ok on smugmug. If you need any measurements checking on my original against your re-made one, just ask. It is sat on the bench at the moment awaiting the plated bits coming back from the platers, so it's no problem. I don't know if new slides are available, but would imagine it is critical that it is correct.

I have no experience running or setting up an R62, that pleasure awaits me, but sorting the R11 (SUM carb) have found a need to richen the mixture from the original jets spec when running the ethanol (5%) fuel we have here in the UK. It missed a little when under acceleration at similar speeds until it was made richer.

  • img_0285.jpg
  • img_0286.jpg
Darryl.Richman
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Ian, would you mind showing

Ian, would you mind showing us a photo of what the connection between your slides and their cables looks like? Like Scott, the cables are permanently connected to the slides in my carburetor. It's not a problem for casual use, but I would really like to be able to disconnect the cables from the slides without having to carry a soldering iron, on the Cannonball.

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Ian R11
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I have tried to answer today

I have tried to answer today but reply has been referred to spam filter. Thought it may be me mentioning n.pples a lot.

Let me know if I need to try again.

Ian R11
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Photo of old ends. Both cable

Photo of old ends. Both cable ends are the same.

The cable is 1.2mm. The cable end is 10mm long and 4.5mm diameter reducing to 3mm. 3mm section is 7mm long.

Washer is 7.6mm overall diameter, 3mm hole, and 1.2mm clear slot. The washer is a good fit, slips over the cable and pushes onto the cable end. I believe they are called "pear nipples" over here.

The cable adjusters are at the platers so can't check, but I am sure the cable end passed through them enabling complete cable removal. You would be able to carry spare cables ready made with these cable ends. When making mine, I will look at the possibility of using plastic or nylon covered inner cable. Modern cables with it seem to have a good life span.

I have kept an eye on the cannonball site and blogs, and amazed at the support and prep people are doing. Rather naively I presumed you just turned up with a well prepared bike and set off. When over, it would be interesting to know the entrants total costs from both ends of the scale, fully supported team against individual entrant. Can then decide if it goes on the bucket list.

I wrote this using the ni...e word instead of cable end. It wouldn't accept it so trying again using CABLE END

schrader7032
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OK Now

Ian R11 wrote:

I have tried to answer today but reply has been referred to spam filter. Thought it may be me mentioning n.pples a lot.

Let me know if I need to try again.

I've reset one of your posts to "not spam".

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sblaylock
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Ian, I would like to get some

Ian, I would like to get some measurements from your original, but I'm out of town until Monday so I probably won't be back online until then to reply to anything you send.

My main interest is the size of the idle jet hole up from the bottom. Mine has a larger bore for the wider part of the jet, then a smaller bore for the slender top part. What is the diameter, and how deep is the wide bore hole? As I mentioned before my slide gets lifted by my idle jet, which makes me think the wide bore hole needs to be deeper. Does the jet hole end at the cross drilled hole through the slide, or does it go past that.

One last thing, can you tell me what the diameter of the cross drilled hole through the slide is.

Thank you for the help,
Scott.

Ian R11
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Thanks for resetting, I

Thanks for resetting, I wondered if it had picked up on some words and not liked them for family viewing! I have no idea how these things work.

Any spare cable will need cable adjusters fitting, the cable end only just fits through the threaded hole on the carb top and won't go through the adjusting screw.

Will post measurements shortly.

Ian R11
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Hope this drawing is ok for

Hope this drawing is ok for your needs.

The hole you need starts as 6mm diameter, 7.9mm deep and continues at 4mm diameter into the cross hole starting at 4mm diameter and reducing to 1.9mm diameter. It ends in this cross drilling. Note this is also cross drilled out of line with the 4mm starting hole. I don't know if it's a manufacturing defect or correct. I have not included the tapered parts on the drawing.

Let me know if you need more info.

  • r62_carb_slide.jpg
sblaylock
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Ian, Thank you for this. When

Ian, Thank you for this. When I get back home I'll compare it to what mine looks like and let you know the results.

I really appreciate you taking the time to get these numbers. It will definitely help me to work through the issue I'm having with my carb.

Sincerely,
Scott.

sblaylock
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Clip Connection

Darryl.Richman wrote:

Ian, would you mind showing us a photo of what the connection between your slides and their cables looks like?...

Darryl, This is how both my slides connect to the cables. They are not permanently connected.

I hope this helps,
Scott.

  • slide_clip.jpg
  • slide_clip2.jpg
Ian R11
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This photo should have been

This photo should have been attached to the posting with cable end measurements that got lost in the spam filter. Same as above, sorry it's late but didn't notice it missing.

I have not found any coated inner cable yet, but have found a supplier of teflon lined outer cable.

  • img_0288.jpg
Darryl.Richman
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Thanks for the photos, guys,

Thanks for the photos, guys, this is very helpful to me.

I've been buying cable parts from Flanders Co. for my prewar bikes. I need to order more stuff to make up some extra cables for the R52 so I'm not trying to solder them together while on the trip.

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sblaylock
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Slide Measurements

Ian R11 wrote:

I have not included the tapered parts on the drawing. Let me know if you need more info.

Hi Ian, The numbers for my slide are mixed. Some are bang on, and some are way off. The depth for the idle jet was one of the numbers that was off so that explains the jet lifting the slide.

Do you still have the slide out of the carb? Could you get me the numbers for the tapered parts? I have a machinist who thinks he can build a new one. Now that I have mine off the bike, I can see there's a hole from the cross drilled hole to the spring retaining hole. Someone tried to solder it closed, but it's still leaking air (see photos). I'll see if I can fix it.

Scott.

  • home_built_slide.jpg
  • home_built_slide2.jpg
Ian R11
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Slide taper measurements

Hi Scott

That hole can't help, but should be easy to block. I think I have all the measures on the sketch, let me know if you need more.

My slide does look original and I hope this is not a "blind leading the blind situation", as I have not run this bike yet!

  • img_0302.jpg
  • img_0301.jpg
  • img_0300.jpg
  • r62_carb_slide_taper.jpg
sblaylock
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Thank You.

Hi Ian, Thanks for taking the time to get the measurements. I talked to the machinist and he was asking if I could get him a few more photos; one of the bottom where the spring slides in, and one of each end of the cross drilled hole - the one you said has the inner hole that goes top to bottom.

With the two drawings and the photos he thinks he can build a version that's really close to your original.

Thank you for all your help with this.

How long until you get your R62 assembled and out on the road?

Sincerely,
Scott.

Ian R11
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Slide photo's. The two side

Slide photo's. The two side on showing the offset inner hole, and both ends.

In the photo with the pen I have tried to centre the inner hole and show it's relationship to the outer hole. The other I have tried to centre the outer hole.

Also one showing direction in relation to peg

  • p1030047.jpg
  • p1030055.jpg
  • p1030057.jpg
  • p1030062.jpg
  • p1030063.jpg
sblaylock
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Hi Ian, Thanks for sending

Hi Ian,

Thanks for sending the last few shots. With all the photos and the drawings I'm sure the final product will be close to yours. I received the jets and seals today from Dreher so hopefully that will help make the bike run smoother.

Thanks again for all the help with this Ian. I really appreciate it.

Sincerely,
Scott

Barry Robin
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Scott-I know it's been a

Scott-I know it's been a while on this thread, but I was wondering how the machinist worked out with your slide redo? Did it fix the problems or was it, as Ian suggested, a case of the blind leading the blind?

In taking another look at the thread, I only just noticed that my slide doesn't have that scalloped vertical notch on the side that has the locating pin. Strange. I always wondered why my carb runs so rich...i mean so rich that it fouls plugs in about a day or so. Any Ideas on if this might be the reason?

-B

sblaylock
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Sorry for the delay in responding

Hi Barry,

As I'm sure you have gathered, I don't check this forum all that often and just now saw you question.

The slide made for me was perfect. I ran the bike in the 2014 Cannonball without any issues and I still drive the bike regularly without an odd throttle problems. The one I had made matched the measurements Ian provided. I did receive a full suite of jets from Dreher and installed the correct ones for my R62. Unfortunately, I can't remember where I found the recommended sizes for the different bikes. I think I went with Darryl's recommendation of 90 for the main, but I can't remember what I went with for the idle jet. Sorry.

I would say if your carb slide doesn't look like the ones in the picture, that could be your issue. Those "scallops" are critical to getting the correct mixture throughout the full movement of the slide in the barrel. You may want to see if you can have one made based on the the measurements provided by Ian.

With the correct slide and jets, I didn't have any issues in the Cannonball... well, not carb related issues. I ran the same jets all the way across the US, including up and over Loveland Pass at 11,990 ft (3,655 m). I was fully expecting to re-jet for the mountains, but it would seem the BMW engineers had that issue sorted - perhaps something to do with the "scallops".

Again, sorry for the delay in replying,
Scott.

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