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Roadster Fouling spark plugs

Started by Raulmanny, January 02, 2014, 03:59:07 PM

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Raulmanny

Roadster, 1984 w/ about 67K. Stock Keihin carburetor and original jets. I'm having a fouling of the plugs problem. Every 100 miles or less I got to change the plugs. The top of the pistons shows (I'm able to scrap thru spark holes) the soft residues of unburned combustion. I DO NOT HAVE any smoke out of the pipes (supertrapp w/ 25 discs each). It looks to me that i'm getting a much too rich mixture or too much gas altogether. Maybe I should replace the jets? Or do I need a new carb? I remember that I used to get 200 miles on a fuel tank (almost 4 gallons). Now, I can not get 150 miles per tank.
This fouling problem is getting on my nerves, please help! 

Wicked

If both cylinders are the same and there was no changes by you or anyone else before this problem started, I'd say you have a stuck float or choke stuck closed. Time for a carb service....

Hillside Motorcycle

Quote from: Raulmanny on January 02, 2014, 03:59:07 PM
Roadster, 1984 w/ about 67K. Stock Keihin carburetor and original jets. I'm having a fouling of the plugs problem. Every 100 miles or less I got to change the plugs. The top of the pistons shows (I'm able to scrap thru spark holes) the soft residues of unburned combustion. I DO NOT HAVE any smoke out of the pipes (supertrapp w/ 25 discs each). It looks to me that i'm getting a much too rich mixture or too much gas altogether. Maybe I should replace the jets? Or do I need a new carb? I remember that I used to get 200 miles on a fuel tank (almost 4 gallons). Now, I can not get 150 miles per tank.
This fouling problem is getting on my nerves, please help!

At that many miles, on that engine, I'd suggest a leakdown test, and perhaps a compression test.
Just from what we have seen here over the many years, your probably past due to have the top end re-built, and if I were to bet, I'd bet your valve guides are beyond worn, for starters.
I'd also check those lifter wheels if you pull it down.
Scott
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

rigidthumper

Another check is if you have a vacuum petcock, ( and I don't remember what year they started) the diaphragm will develop pin hole leaks, allowing raw fuel to be sucked into the carb manifold via the vacuum line, adding a lot of extra fuel that isn't wanted. Quick check is to pull the vacuum line off and see if it's wet after a ride. If so, new petcock and all should be well again.
HTH
Robin
Ignorance is bliss, and accuracy expensive. How much of either can you afford?

nucklhead13

You ought to find an old Iron Head repair manual. one of them usually has some pictures of spark plug ends. They show those so you can see the different colors that happen and what causes that to happen.

garyajaz

first is to determine if oil fouled or gas fouled or both.
what do the ends of exhaust pipes look/feel like?
soft and sooty or oily?

if dry and sooty (gas) wicked and or ridged called it.
since it got good mileage prior I would not change jets.
they usually don't wear larger....lol

if oil fouled scott got it.
these things seem to eat guides.
either way top end may need tended to at your mileage.

my rarely ridden sporty fouls them often.  I carry spare set.
I have bronze alum guides set up loose . oil into chamber.
stroker forged pistons, loose clearances lets oil by. 

add to it a S&S L series carb that is rich for "personal reasons"
I gas foul if not running hard like it was rebuilt for.

mine dosent smoke but does puff on decell cause of no seals on guides.
hell, even fresh set up to race they puff on deceleration.
good luck.

it dosent take much to pull off a head and cylinder and check rings, valve seal and stuff.
I would check the fuel system first cause of less work involved.
simple stuff first.

67K miles and never been opened up?
hell it needs a top end anyway.