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'75 R90/6, Bing Carbs, inconsistent spark plug appearance

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Scott Lindroth
(@18392)
Posts: 8
Active Member
Topic starter
 

1975  R90/6, original Bings.  I've owned the bike about 1.5 years.  It had 27K miles at purchase.  It has 38K miles today. 

The left spark plug runs dirty - looks like it's running rich, but it's easily cleaned.  The right plug accumulates crystalized carbon deposits on the electrode, though the center insulator is white-ish.  The right plug also has oil on the threads. 🙁

I rebuilt the carbs less than 1 year ago.  I also rebalanced the carbs with a Twin Max meter. 

Despite inconsistent plug appearances, the bike seems to be running well. 

I realize that there are (at least) two different issues here.

To deal with the rich condition, I dropped the jet needle a click on both carbs.  No noticeable difference based on plug inspection.  Bike seems to run equally well, but the left plug is dirty and the right accumulates crystalized carbon.

As for oil on the right plug, maybe it's time for new piston rings?  Or maybe the valve seats are worn?  I can deal with the rings, but the valve seats...

Thanks for your thoughts the difference between the two cylinders/carbs.

Scott 

P.S.

Additional but possibly irrelevant context:  Bike came with a Dyna III ignition, though it used the OEM 1K ohm spark plug caps. A couple months ago I installed the EDL4 450W charging system, and and last week the EDL4-IGNS electronic ignition.  I just realized that the bike needs 5K ohm caps - hope the new ignition system hasn't been compromised by the 150 miles I put on since installing it!  The bike seems to be running great. 

The spark plug issue has been present since I purchased the bike.

This topic was modified 2 months ago by Scott Lindroth
 
Posted : 03/23/2024 13:30
David Elkow
(@4949)
Posts: 304
Reputable Member
 

One factor involved is the crankcase ventilation system. I’m not sure of the configuration used for your bike, but it likely dumps into only one of the carb intake tubes.  That side may persistently look blacker, depending on the mileage / condition of the rings. Really not anything to be too concerned with, as long as your compression is ok / oil consumption reasonable / runs well / etc.  Just a thing. 

Dropping the needles a notch is a big step leaner.  I would confirm that the jetting for your bike matches the Bing chart. The chart goes by carburetor numbers. Your carb numbers are stamped on the casting web above the exit end of the carburetor. I’m attempting to attach a copy of the Bing chart, or you can find it at bingcarburetor.com  .  

Another factor with these bikes is parking on the side stand.  Shutting the bike down and parking on the side stand will inevitably introduce some oil into the left cylinder.  Oak O. recommended (if you are gonna use the side stand) to shut it off, lean the bike to the right and count to ten, then park it on the side stand.  

 

 
Posted : 03/23/2024 15:36
David Elkow
(@4949)
Posts: 304
Reputable Member
 

PS: The needle notch on the Bing chart is called “clip position”. 1 is most lean, 4 most rich. 

 
Posted : 03/23/2024 15:57
Steven Rankin
(@14724)
Posts: 197
Estimable Member
 

David has given some good insight into perhaps what your problem is.

Plug color can change mildly depending upon riding conditions.  Traffic and stop and go will look different sometimes than country riding.

I find the best way to check plug color is to take a long ride in the country with few stops and idle, then as soon as I am in the garage pull the plugs and check.   

You don't have nearly enough miles on the bike to warrant a rebuild.  

Before you ever do a rebuild do a compression check with the carbs off or better yet a leak down test.    

Unless compression drops or oil consumption goes up significantly, don't worry. Have fun riding, St.

 

Beware! I do not suffer fools gladly! St.

 
Posted : 03/24/2024 07:59
Richard W
(@wobbly)
Posts: 2545
Member
 

Your bike is coming up on it's half-century birthday. Also, to have that low of mileage, the bike has had to do a lot of sitting. Agreed, that's not very old for an Airhead, but that's not the way we need to look at this situation. Instead ask yourself this question: "How many 1975 (or earlier) cars did you see this last week ?" Proabably none. So you've got a lot of regular maintenance due to sitting and age.

All the suggestions above are valid, but maybe not in the order I would suggest. Let's look at some maintenance priority rankings...

• First of all you're proabably not running 1975 fuel any longer. The new (since ~1990) Ethanol fuels are your greatest concern. These Ethanol fuels cannot be allowed to sit in the tank or carbs for longer than approximately 8 weeks. You can Google "phase separation" to learn more.

When they do, they attract water which does a "number" on the carbs. A coating starts to form which covers everything. This coating closes off the fuel jets and passages, which in turn make the bike run lean and robs power. Look at the inside of your float bowls. If you have ANY coloration other than Bing gray carb metal, then you have trouble. 

?1

• The ignition system ages and original parts MUST be replaced. The requirements for these parts come from 1975. Modern equivalent parts will not work. Simply due to their age, it's time to replace the plugs, plug wires AND plug caps. I highly suggest 2 new NGK BP7ES plugs (and no other), replace both plug wires with metal core wires (do not fit modern "suppression wires"), and replace your old resistor plug caps with modern ones. (Most people are using NGK 5,000 (5K) Ohm right angle caps. Or you can get a new plug wire & cap set from Motorrad Elektrik.) 

• While the older R75 breathers DO need to be updated to the latest model breather valve (see Snowbum for this), the biggest reason breather oil gets into the intake is 1) dirty air filters and 2) wrong engine oil. Your oil should be API rated SF or SG 20W50, such as Valvoline VR1.

• Another common problem is that carb needle clips after 50 years can be in mis-matched positions. Not only check the needle clip positions, but ALSO that the needles protrude the same amount on both slides.

You can also look here for additional tips on Airheads that have sat for a long time:

https://www.airheads.org/community/wrenching/new-owner-primer-tips-to-get-your-airhead-back-on-the-road/

 

Hope this helps.

This post was modified 2 months ago by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 03/25/2024 05:06
Steven Rankin
(@14724)
Posts: 197
Estimable Member
 

Scott, if you get a chance could you post some pictures of your plugs so we can see if this is a case of normal airhead behavior or something in need of Richard's drastic measures?

 

Beware! I do not suffer fools gladly! St.

 
Posted : 03/25/2024 07:28
Scott Lindroth
(@18392)
Posts: 8
Active Member
Topic starter
 

Thanks all - this is very helpful.  I'm waiting until the 5K ohm caps arrive before riding the bike again.  I'll post pictures of the plugs afterwards.  This is the first I've heard of a crankcase breather valve - time to go through my Haynes manual (and Snowbum, of course).

The carbs are clean.  They were rebuilt with a new float needle, gaskets, diaphragm - adjusted the tang on the floats, etc.  I measured the jet needles carefully, so I know they are pulled out the same amount.  I'm planning to inspect them again as riding season approaches. I'd be glad not to replace the rings now but one of the pushrod seals weeps on occasion so I have to pull the cylinders off anyway.

I only use 93 octane E0 gas (lucky to have a station nearby).  

Again thanks for the tips.  I'll post with more info when I have it.  

This post was modified 2 months ago by Scott Lindroth
 
Posted : 03/25/2024 13:55
Steven Rankin
(@14724)
Posts: 197
Estimable Member
 

For your upcoming replacement of push rod seals, you can slide the cylinder out enough to replace without taking it completely off.  

Again, unless you see a bad compression reading or leak down result, don't spend the money on an engine rebuild. St.

 

This post was modified 2 months ago by Steven Rankin

Beware! I do not suffer fools gladly! St.

 
Posted : 03/25/2024 14:33
Richard W
(@wobbly)
Posts: 2545
Member
 

• The new style breather is preferred because the /5 version used a phenolic disc as the flapper. After opening and closing a couple of million times the flapper becomes worn and does not make an effective seal. The newer design uses a stainless steel reed valve which stands up to long-term use and has no issues with long-term sealing or back-flow.

• Piston rings are replaced due to excessive end gap. Compression and oil consumption issues are usually taken care of by simply taking the motorcycle on a couple of long road trips. 

• One thing we need to ask is for Scott to describe the full process leading up to the plug removal and reading process. 

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 03/26/2024 05:52
Steven Rankin
(@14724)
Posts: 197
Estimable Member
 

Yes Richard, we should look at pictures and get more data before telling Scott to do what could be  a lot of work for nothing. 

Also, this is a /6 not a /5, so I don't think there is a real need to go changing the crankcase breather unless it has failed.  So FAR, there is no indication of that.  St.

Beware! I do not suffer fools gladly! St.

 
Posted : 03/26/2024 06:15
Scott Lindroth
(@18392)
Posts: 8
Active Member
Topic starter
 

Thanks for your help!  Maybe the easiest thing to try up front is running with a bit less oil - I read elsewhere on the forum that this may reduce the amount of oil mist getting through the breather valve.  I have a "deep" pan and usually fill it to the "nicht über max" line.  I'll try halfway full and see if it makes a difference.  

The 5K ohm spark plug caps arrive on Saturday - can't wait to get 'em on the bike.  

After rebuilding the forks, brake caliper and master cylinder, installing a headlight and signals, replacing the clutch, starter, charging system, and ignition, I'm hoping that the to-do list will trail off... 😊   All that said, there have been extended periods of pleasurable riding, including up to the National Rally in Doswell last June.  I've enjoyed working on the bike. 

Again, thanks for the suggestions. 

- Scott

 
Posted : 03/26/2024 16:03
Richard W
(@wobbly)
Posts: 2545
Member
 

Posted by: @wobbly

• One thing we need to ask is for Scott to describe the full process leading up to the plug removal and reading process. 

An owner can't simply "pull the plugs" at any random time and expect to take a meaningful "plug reading". Before you go through the trouble of posting photos, a description of your process would be nice. 

The correct process is to ride at a fixed RPM for at least 5 miles (and hopefully more), hit the "kill switch" while at the same time disengaging the clutch so that the engine stops turning, then coast to the side of the road and pull your plug(s). This results in a reading for a specific jet (needle jet or main jet). The standards for each are known and defined.

However, if you allow the engine to idle the reading will be useless. The jetting for mid-range and high-speed are precisely defined for efficient combustion, whereas the settings for idle are to achieve consistent idle so that the engine doesn't die at traffic stops. There is not one, single correct reading for idle mixture, because that would vary widely from engine to engine. 

So if you just decided to pull your plugs one day and look at them, then of course they look questionable because a questionable procedure was used to obtain the reading. GIGO.

Hope this helps.

 

This post was modified 2 months ago by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 03/28/2024 08:06
Scott Lindroth
(@18392)
Posts: 8
Active Member
Topic starter
 

Thanks, Richard.  I understand the idle circuit in the carb is different from the others.  The hope is to get it out for some country riding next week(end).   -- Scott

 
Posted : 03/28/2024 13:25
Steven Rankin
(@14724)
Posts: 197
Estimable Member
 

https://ngksparkplugs.com/en/resources/read-spark-plug

I looked at a couple of  spark plug sites, NGK, and Champion.  I also did a search through Snowbum's website and found nothing in regard to the proper removal and conditions for reading spark plug color.  

I am seeing that random spark plug removal is useful and not garbage.  

While the method of riding for a period of time and killing the engine then pulling over to the side of the road and removing spark plugs sounds like a proper way to do things, I am NOT seeing that method mentioned in the plug companies literature, nor do I see it in Snowbum's site.

St.

Beware! I do not suffer fools gladly! St.

 
Posted : 03/28/2024 16:31
Richard W
(@wobbly)
Posts: 2545
Member
 

Posted by: @14724

I am seeing that random spark plug removal is useful and not garbage.  

1) No one said it was "garbage" or absolutely useless. Please stop mis-quoting others and/or blowing their comments out of proportion. 

2) A lot of standard shop practice and knowledge is not documented elsewhere. Show me where the BMW literature says their plug caps have issues after 40 years. Show me where Bosch or NGK says to lubricate their spark plug threads before installation into an aluminum cyl head. 

There are a lot of things you know that others don't. There are a lot of things that others know that you don't. Sharing this knowledge is the power of the Community. However, the tone of some of your input tends to be adversarial. This is not helpful to the goals of the Airhead community and this Club. Every statement here doesn't need your editorial comment. Please stop it.

 

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 03/29/2024 05:49
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