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Old 09-04-2011, 09:37 AM   #1
DandyDoug OP
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Spark plug fouling ???

Bike is a 1985 BMW R80:

Pulled the spark plugs due to a slight misfire, found the right plug coated in black soot and oil, the electrode was fouled with what looked like carbon. The left plug was dirty black but still functional.

Changed plugs ( Champion RN9YC) ran some Seafoam through a tankful of gas and added a small amount in to the crankcase.
Went for a 300 mile ride, no engine misfire, fuel consumption is normal, bike pulls strong in all gears and runs fine at both highway speed and around town.

Pulled the plugs for a look;
the right plug is black on one side of the electrode and medium gray on the other side ???
the left plug similar but not nearly as black ?

Have not done any carburetor adjustments, and do not know what jets are in them, both are OEM Bing's.

Helpful suggestions appreciated as to what the next move should be.
Thanks, Doug
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Old 09-04-2011, 10:04 AM   #2
SOLO LOBO
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Time to tune your carbs.... at a minimum. re-baseline and re-synch. If you have access to the tools, test the compression.

How's your airfilter btw?

Seafoam doesn't address tuning issues, and doesn't tackle the bad deposits that can occur in Bings.


As an FYI, I end up re-tuning my Bings every few thousand miles. OK, I like messing with them and it isn't totally needed.
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your bike is suitably dirty. Well done.
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Old 09-04-2011, 04:02 PM   #3
DandyDoug OP
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Exactly what do you do, when you say you "tune your carburetors" every few thousand miles ??

I have never messed about with Bing's before, never needed to ?????????
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Old 09-04-2011, 05:06 PM   #4
JamesOn2Wheels
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fouling

If your plug has oil on it, then you've got an oil leakage past compression issue...either past rings or valve guides.
I would have guessed the left plug to be oil soaked if you use a sidestand.
The carbon is of course unburned or partly burned gas...is your idle mixture screws turned out more than 3/4 turn (like mine....) - it can blacken your plugs even with a few minutes idling.
If after adjusting or cleaning carbs you still have the issue, maybe time to look at a compression test or leak-down test to get more information.
It sounds like your carbs are running too rich too ...time to clean them as your bike is running rich at speed, usually due to dirty/gummy slides etc...

Have fun

maybe a hotter plug would be in order too N9 is kinda cold isn't it ?
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Old 09-04-2011, 06:53 PM   #5
DandyDoug OP
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It's the right side plug that was the worst of the two. I do use the side stand occasionally , but when parked in my garage it's up on the center stand.
I looked at my Haynes manual but it's not clear which screw is the idle mixture ?

According to the maintenance list I got from the PO. the carburetors were rebuilt in Oct of 09 with a mileage indicated of 4057,
the bike now has a bit over 7000 indicated. ( as far as I can tell it's had at least two speedometers since new, so the actual mileage is unknown)
I think it would be unlikely they need to be rebuilt again so soon ??

As to plug heat range hmm , I'm not sure which way to go.
The plugs that were in the bike when I bought it were NGKBP7ES.

The Champions I replaced them with RN9YC were what came up on the computer at the parts store as a match for replacement.
What do you run in your machine ??
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Old 09-04-2011, 07:26 PM   #6
JamesOn2Wheels
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I have an 83

I'm running BP6HS non resistor NGK's but I think you can run resistors if I'm not mistaken...

Under your carbs at the front (nearest cyl) should be a spigot for vacuum balancing, and next to it the idle mix screw in a housing that looks like a alu tube casting about pencil dia......you kinda have to stand on your head to see it...unless the newer bikes don't have it - someone will know.

Turn it in all the way and back out to 3/4 -7/8 and then with motor hot idling adjust by ear - I'm at 1 1/8 turn out but that is maximum in my opinion...will idle a little rich but won't backfire or fart on you when taking off...

I wouldn't run Champs....people whisper about them mucking the threads in the head....if you can run resistors in yours go for Iridium plugs...they're about 7 bucks at parts stores and are pretty incredible and last 30K miles...
but I think you have too cold a plug ...6 or 7 range (8 in Bosch) is right

'luck

James
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Old 09-04-2011, 08:23 PM   #7
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it does sound too soon to have to re build teh carbs, but cleaning and tuning is easily done.

Are you sure the wetness on the one plug was oil and not gas? If it was oil you have a bigger problem, I think but if its just wet gas and carbon then your running rich, which is pretty easily fixed, or one off your plugs or wires or something related to that is wonked. Double check the air filter, too, since thats easy.
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Old 09-05-2011, 09:32 AM   #8
DandyDoug OP
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I Googled spark plug heat ranges and found some interesting info;

The European and Japanese plug makers use a range from 2 to 12, with the" lower" numbers being the hotter range.

The US makers, Champion and such use a range from 2 to 12 with the "upper" numbers being the hotter range.
Just thought that was interesting.

Read my owners manual, the OEM recommended plug's are either a Bosch W7DC or a Champion N-9YC.

Since I am currently running the Champion RN9YC they should be in the correct heat range.
I will try and find a set of something hotter this next week and see what that does, then start mucking around with the carburetors.
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Old 09-05-2011, 09:37 AM   #9
Strong Bad
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I personally think that to gasoline foul plugs that quick your carbs would have to be waaaaay off and it would run like shit as a result. You are most likely burning oil to leave deposits like that.
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Old 09-05-2011, 11:09 AM   #10
DandyDoug OP
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The motor runs strong and I have had it up to about 90mph a couple of times.
I consistently run it at 3800--4500 rpm .

It does use a bit of oil, less than a quart in 700 - 1000 miles.
It does not smoke on take off or on down shift, no backfire when I close the throttle after a hard run, and no smoke at that time either.
No leaks visible.
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Old 09-05-2011, 11:11 AM   #11
SOLO LOBO
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Changing the plug heat range isn't going to solve the issue, something is worn or out of adjustment.

Start with the free things first.... Make sure your carbs are correctly tuned and synched, and that the air filter is clean. Check the timing and get the bike in the best possible tune.

If you continue to foul plugs cheek the breather for excess oil, check the compression and see what you find
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your bike is suitably dirty. Well done.
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Old 09-06-2011, 02:16 AM   #12
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Quote:
Originally Posted by DandyDoug View Post
It's the right side plug that was the worst of the two. I do use the side stand occasionally , but when parked in my garage it's up on the center stand.
I looked at my Haynes manual but it's not clear which screw is the idle mixture ?

According to the maintenance list I got from the PO. the carburetors were rebuilt in Oct of 09 with a mileage indicated of 4057,
the bike now has a bit over 7000 indicated. ( as far as I can tell it's had at least two speedometers since new, so the actual mileage is unknown)
I think it would be unlikely they need to be rebuilt again so soon ??

As to plug heat range hmm , I'm not sure which way to go.
The plugs that were in the bike when I bought it were NGKBP7ES.

The Champions I replaced them with RN9YC were what came up on the computer at the parts store as a match for replacement.
What do you run in your machine ??
BP6ES in my r100rs. Should be the same for you, but the oil description still sounds like too much.
Underneath the carb (b/w carb bowl & head) there are two protrusions pointing down. The bigger of the two is the mixture screw. The other is the vacuum port.

http://www.ngk.com.au/sparkplug_bike...W&Engine=800cc

boxerboy81 screwed with this post 09-06-2011 at 02:31 AM
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Old 09-06-2011, 02:13 PM   #13
DandyDoug OP
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Thanks for the info !

I am borrowing a compression test gauge and a carburetor sync tool from a friend and have ordered the NGK plugs.
Should get it all by tomorrow .

Will post the compression results then.
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Old 09-06-2011, 06:00 PM   #14
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How long were the old plugs in the engine?

How long has the bike been misfiring?

Was the bike hot or cold when misfiring?

Did you do anything to the bike immediately before it started misfiring?

Was it wet out?

Could be the stumbling is not all that related to the fouled plugs. Could be the plugs are a symptom of the greater problem and not the cause.

How long have you had this bike?

Do you have any symptoms of pinging or detonation?

You say there's no smoke out of the exhaust, have you had somebody watch, or have you just not seen any?
A lot of times I've seen smoke at night, where during the day I don't see it. It's weird but you can pick it in headlights.

Best thing to do, base line everything
Make sure the valves are adjusted, make sure the ignition system is 100% including Coils, plug wires, Bean Can and plugs.
Make sure the compression is good, within range. I would hurt anything but your pocket book to also do a leak down.
The carbs. Make sure they are adjusted, float height, balance, make sure the slides are working as they should.

The crankcase breather system, BMW routes the crankcase vapors and oil mist right into the intake tract, it's not unusual to see some oil siting in the intake runner especially on older higher mileage bikes where there's some blowby.
This can manifest itself as oil in the combustion chamber if there's a lot of blowby gasses/oil coming out of the breather.
Re routing the breather doesn't solve the underlying problem, how ever, for that you would still need some top end work.

I say this as the plugs on the wife's R80 also look a little carbon fouled. But other then showing signs of needing to be decarboned, it runs strong. I know her bike is a little loose on the top end and there's carbon build up and a fair amount of blowby gasses.
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Old 09-06-2011, 07:21 PM   #15
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My ST likes to blow a little oil out the breather at Interstate speeds. In my case more oil mist goes to the left carb and that plug fouled in the 1400 mile trip up to the MOA. Plugs looked as you described, just swapped sides. To get that much fouling (motor was idling rough when I got to the Rally), I blew/burned a total of 1.5 qts in 2800 miles, which is within BMW service limits. This is the first time the ST has maintained Interstate speeds almost 20 hours over two days and the highest oil consumption so far. It has always blown a little over accumulated high speed miles, but this was the first time it actually fouled a plug to the point of barely able to keep running at idle.

I run NGK BP6ES non resistor plugs and Accel resistor wires (Hey! they were hanging on my pegboard already) to avoid RFI interference to the ignition module. The plugs are just a couple of bucks at my local Advance Auto Parts and they always are in stock.

Valves are still in adjustment, hot compression as of this week is 130 left/134 right, and the telltale that its coming from the breather is the way the whole interior of the left carb is oiled up, as is the air intake tube leading into it.

Take a look inside your carbs, check the valves before doing a compression test, compression test, leakdown if needed, and clean the carbs. I have read on here and other sources, and heard it said/saw it demonstrated at Airhead Central at the MOA Rally that its a good plan to make carb cleaning and inspection an annual task.

If you find only the right carb oiled up from end to end, inspect the molded rubber breather tubes from the tee inside the airbox to where they dump into the runners going to the carbs - one of mine was split from age when I got the bike (and was oiling the inside of the airbox.

That's all the free advice I can afford right now. Good luck chaisng it down.
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