Semi-restoring a 1978; Need advice about best sequence? (long)

[R100SinLA]

Hi folks
1st post … some photos attached below

Background about this motorcycle:
1978 BMW R100S
Matching numbers
Factory production date 12/1977 According to info found online
Odometer approx 15,000 miles believed to be true
Purchase: 11/2023 locally (Los Angeles) from second owner. (No service documentation supplied). Seller says he purchased from original owner In SoCal in 2021 or so.

Appears to be true low miles bike (15k)
Appears to be factory/stock mechanically except:
Boyer Bransden electronic ignition system installed by a previous owner probably decades ago (BMW - Type MK 3)

I have not touched/adjusted carbs since acquisition…seller said he went to local airhead ‘guru’ for carb adjustments…

Current status:
Runs pretty well
throttle feels subpar
idles ok but only after completely warmed up (1300-1400 at idle according to tach)…yes it’s probably too high.
Handling is good so far…under 60 mph only.

So, I’m about to start the following work and have all parts/materials ready to go:

-not in any particular order-

Check/adjust timing
Check/adjust valve clearances and rocker arm end play
Check for air leaks all around carbs (spray brake cleaner test)
Install new (correct??) spark plugs- BOSCH W5DC (currently NGK BP6ES)
Install new (stock BMW) plug wires
Service/lube throttle control
Install new (stock BMW) throttle cables
Install new (stock BMW) choke cables, service choke lever (airbox mounted)
Disassemble/complete rebuild Bing 40 carbs (all parts from BMW)
Synchronizing carbs

So here’s my problem/question:
Seeking advice as to the best sequence of the above tasks.

My main concern is making sure I have a decently running bike to take those required 5-10 mile warm-up runs prior to some of the tasks. (Will be first time working on Bing carbs)

Have been studying/following Snowbum’s writings diligently (Thank you Snowbum!!)
And also William’s videos from Boxer2valve (Thanks William!!)


MORE INFO:

Work completed by me since acquisition (11/2023):
1. All fluids changed including fork oil
2. Sump pan removed, cleaned and new gasket/bolts installed
3. Air filter (mahle) installed
4. Front brake system (dual disc) serviced/rebuilt including new rubber hoses, MC & calipers rebuilt
5. Front forks serviced (rebuilt) & new factory springs
6. Dual horn system installed, including new harness/ relay/ fuse
7. Factory “S” fairing, nice condition (sourced, previously painted black) installed, factory volt gauge & clock (like new) sourced, & custom (by me) quick-disconnect harness with connector
8. Installed front turn signals/correct wiring
9. All new bulbs installed (except not inside instrument cluster)
10. New fuses installed in headlight bucket
11. Sorted/checked connections in headlight bucket
12. All known grounding connections on frame sanded cleaned up
13. New starter relay & new voltage regulator installed
14. Many assorted rubber bits/grommets/washers/bumpers/rings/etc replaced
15. Luggage mounts (Reynolds) installed
16. New gloss black paint work by outside shop (tank, seat, fr fender & side covers)

Cheers
JC

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[gspd]

The very first thing should be a compression test to establish what you're working with.

"Odometer approx 15,000 miles believed to be true."
hmmmmm.....
The bike actually looks really nice, please excuse my skepticism.
To quote the band Journey:
Don't stop believin'
Hold on to that feelin'

[SteveD]

Welcommen

Congrats...the bike looks sensational.
15Kmiles does lead to a and though. Still, it looks great.
Do you have a history with airheads? In case you're new to the foibles here's a couple of bits o'info...apologies otherwise.

Check/adjust timing... remove the battery neg from the battery to avoid a short on the diode board as you remove the front cover. I tend to leave the connection at the trans end alone because the thread in there isn't strong.
Check/adjust valve clearances and rocker arm end play. If you do the stud retorque, many will back away from the final torque...eg 2-3ft/lb less than the book numbers to avoid pulling a stud. It happens.
Check for air leaks all around carbs (spray brake cleaner test) intake spigots can be loose too. Less than obvious reason for a high idle.
Install new (correct??) spark plugs- BOSCH W5DC (currently NGK BP6ES) The NGK are just fine. The Bosch were getting hard to get.
Install new (stock BMW) plug wires and consider plug caps too but later if required.
Service/lube throttle control
Install new (stock BMW) throttle cables
Install new (stock BMW) choke cables, service choke lever (airbox mounted)
Disassemble/complete rebuild Bing 40 carbs (all parts from BMW) if it's truly 15Kmiles then the only hard parts to change would be the needles and needle jets. They're prob still ok but if it's all apart and they're cheap...lots of small o-rings otherwise.
Synchronizing carbs... Once tuned, they tend to idle poorly until fully warmed up. They do require a decent warm up ride before doing the carb tune otherwise you'll end up with a high idle.

[R100SinLA]

The very first thing should be a compression test to establish what you're working with.

"Odometer approx 15,000 miles believed to be true."
hmmmmm.....
The bike actually looks really nice, please excuse my skepticism.
To quote the band Journey:
Don't stop believin'
Hold on to that feelin'

Thank you for your advice and compliment. My plan was to do a leak down test when I remove the carbs.
At this time I’m proceeding with the assumption that it’s a low-miles bike. But time will tell…

[R100SinLA]

Welcommen

Congrats...the bike looks sensational.
15Kmiles does lead to a and though. Still, it looks great.
Do you have a history with airheads? In case you're new to the foibles here's a couple of bits o'info...apologies otherwise.

Check/adjust timing... remove the battery neg from the battery to avoid a short on the diode board as you remove the front cover. I tend to leave the connection at the trans end alone because the thread in there isn't strong.
Check/adjust valve clearances and rocker arm end play. If you do the stud retorque, many will back away from the final torque...eg 2-3ft/lb less than the book numbers to avoid pulling a stud. It happens.
Check for air leaks all around carbs (spray brake cleaner test) intake spigots can be loose too. Less than obvious reason for a high idle.
Install new (correct??) spark plugs- BOSCH W5DC (currently NGK BP6ES) The NGK are just fine. The Bosch were getting hard to get.
Install new (stock BMW) plug wires and consider plug caps too but later if required.
Service/lube throttle control
Install new (stock BMW) throttle cables
Install new (stock BMW) choke cables, service choke lever (airbox mounted)
Disassemble/complete rebuild Bing 40 carbs (all parts from BMW) if it's truly 15Kmiles then the only hard parts to change would be the needles and needle jets. They're prob still ok but if it's all apart and they're cheap...lots of small o-rings otherwise.
Synchronizing carbs... Once tuned, they tend to idle poorly until fully warmed up. They do require a decent warm up ride before doing the carb tune otherwise you'll end up with a high idle.

Thanks for your nice words about the bike!

I have no airhead history, so it’s all new. I owned a ‘71 Norton Commando 25 years ago. Most of my wrenching was on a 1969 BMW 2002 and a 1973 BMW 2002tii. Also quite a while ago.

I’m finding the airhead is fairly easy to work on but at the same time complex due to lots of idiosyncrasies and differences between models/years. The usual resources are lacking and can’t really be trusted it seems (clymer and Haynes). Luckily there’s Snowbum and William (Boxer2valve)!! And Brooks.

Most importantly the availability of parts is fantastic (way beyond my expectations).

Also thanks for taking time to pass along the tips in your reply.

[SteveD]

Pleasure. You'll find some excellent advice here and you'll learn to know who has the clues. I'm not necessarily in that echelon but incorrect advice is corrected soon enough.

If you're a wiz with carbs then this is probably too much info. However it does present from the point of view of a carb "newbie" (me at the time) and might be useful. Hopefully so.

http://rossmz.blogspot.com/2008/12/tuni ... r-bmw.html

[jackonz]

Hi folks
1st post … some photos attached below

Background about this motorcycle:
1978 BMW R100S
Matching numbers
Factory production date 12/1977 According to info found online
Odometer approx 15,000 miles believed to be true
Purchase: 11/2023 locally (Los Angeles) from second owner. (No service documentation supplied). Seller says he purchased from original owner In SoCal in 2021 or so.

Appears to be true low miles bike (15k)
Appears to be factory/stock mechanically except:
Boyer Bransden electronic ignition system installed by a previous owner probably decades ago (BMW - Type MK 3)

I have not touched/adjusted carbs since acquisition…seller said he went to local airhead ‘guru’ for carb adjustments…

Current status:
Runs pretty well
throttle feels subpar
idles ok but only after completely warmed up (1300-1400 at idle according to tach)…yes it’s probably too high.
Handling is good so far…under 60 mph only.

So, I’m about to start the following work and have all parts/materials ready to go:

-not in any particular order-

Check/adjust timing
Check/adjust valve clearances and rocker arm end play
Check for air leaks all around carbs (spray brake cleaner test)
Install new (correct??) spark plugs- BOSCH W5DC (currently NGK BP6ES)
Install new (stock BMW) plug wires
Service/lube throttle control
Install new (stock BMW) throttle cables
Install new (stock BMW) choke cables, service choke lever (airbox mounted)
Disassemble/complete rebuild Bing 40 carbs (all parts from BMW)
Synchronizing carbs

So here’s my problem/question:
Seeking advice as to the best sequence of the above tasks.

My main concern is making sure I have a decently running bike to take those required 5-10 mile warm-up runs prior to some of the tasks. (Will be first time working on Bing carbs)

Have been studying/following Snowbum’s writings diligently (Thank you Snowbum!!)
And also William’s videos from Boxer2valve (Thanks William!!)


MORE INFO:

Work completed by me since acquisition (11/2023):
1. All fluids changed including fork oil
2. Sump pan removed, cleaned and new gasket/bolts installed
3. Air filter (mahle) installed
4. Front brake system (dual disc) serviced/rebuilt including new rubber hoses, MC & calipers rebuilt
5. Front forks serviced (rebuilt) & new factory springs
6. Dual horn system installed, including new harness/ relay/ fuse
7. Factory “S” fairing, nice condition (sourced, previously painted black) installed, factory volt gauge & clock (like new) sourced, & custom (by me) quick-disconnect harness with connector
8. Installed front turn signals/correct wiring
9. All new bulbs installed (except not inside instrument cluster)
10. New fuses installed in headlight bucket
11. Sorted/checked connections in headlight bucket
12. All known grounding connections on frame sanded cleaned up
13. New starter relay & new voltage regulator installed
14. Many assorted rubber bits/grommets/washers/bumpers/rings/etc replaced
15. Luggage mounts (Reynolds) installed
16. New gloss black paint work by outside shop (tank, seat, fr fender & side covers)

Cheers
JC

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Thats a nice looking bike, looks like your doing what I did to my 1978 R80/7, seems I have done what you have planned but in my case I had to remove both pots and replace the pushrod tubes with S/S Items as mine were either loose or had rotted through.

I still have to pull my front forks off again as I put the wrong weight oil in last time, I now have the BMW fork oil to cure the issue with a stiff front end.

Good luck with the rebuild.

[Kurt in S.A.]

I still have to pull my front forks off again as I put the wrong weight oil in last time, I now have the BMW fork oil to cure the issue with a stiff front end.

Why do you have to "pull" the front forks off? Can't you just drain the oil that is in there and refill? There will be residual oil but it will mix down to a lower viscosity.

Kurt

[jackonz]

I still have to pull my front forks off again as I put the wrong weight oil in last time, I now have the BMW fork oil to cure the issue with a stiff front end.

Why do you have to "pull" the front forks off? Can't you just drain the oil that is in there and refill? There will be residual oil but it will mix down to a lower viscosity.

Kurt

True, but never thought of doing it that way, all previous bike I have just pulled the legs out.

[Rob Frankham]

Forks after 1980 (those with the Brembo calipers) have a drain bolt specifically for this purpose... the earlier forks don't. To drain the fork legs...

1) remove the top cap of each leg

2) Support the front wheel.

3) remove the rubber cap from the very bottom of the fork slider.

4) Place a container under each fork leg (also a good idea to protect the side of the tyre with a rag).

5) remove the nut and washer that are revealed in the bottom of each fork slider.

6) Remove the support from the front wheel and allow it to drop a little to let the oil drain (without the support, the front wheel and fork sliders will drop because that nut and washer is what connects the moving parts of the suspension to the fixed bits). It is a good ised not to allow the forks to drop so far that the threaded stud disappears inside the slider...

7) Once the oil has drained, raise the wheel/sliders and replace the nuts/washers. Replace rubber caps.

8) fill with oil and replace the tops caps of the legs.

The alternative is to...

1) Remove the wheel, mudguard and brake caliper.

2) Remove the caps and undo the nuts/washers as in 5 above

3) simply slide each slider off the leg.

This is messy because oil will start to drain as soon as you remove the nuts but you can make sure that you get rid of all old oil and any debris that might have accumulated as well as examine the damper components.

The benefit of both of these methods is that you don't disturb the fork alignment & etc...

Rob