fouling plugs

16 replies to this topic
  • onyxxx

Posted October 06, 2002 - 01:05 PM


I have abouy 200 miles on my wr, and this weekend when I went up north to ride, the plug fouled out. I put another plug in it, it ran fine for about a 10 minute test, however the next day when I took it out again the bike was sputtering and backfiring. After about 15 minutes on this ride it seemed to clear up a bit. I did not have time to check plug again but I'm assuming it would be on the black side. The only difference riding this weekend was the weather, I usually ride in 70+ degree conditions in the summer (this past summer 80 to 90), this weekend it was 50 degrees where I was riding. I have uncorked exhaust, no lid, grey wire disconnected, and stock jetting. Would the colder weather make it foul out? I checked the plug at about 100 miles and it was looking pretty black this summer, but running pretty well. The only thing I would notice is a bit of cutting out when on the throttle in about fourth gear. Any info would be appreciated.

  • tk421

Posted October 06, 2002 - 02:34 PM


If you’re like me and powerwash your bike, you need to check for poor connections and moisture within the wiring harness, coil, plug boot, and CDI unit. Compressed air will dry stuff out like nothing flat. It’s amazing how long water will sit in the harness. There’s some stuff called DeoxIT D5 made by CAIG LABORATORIES INC. This stuff works well on corroded electrical connections.

Drain the gas completely and try a different brand.

Install a NEW spark plug: CR8E or the Autolite 4303. Gap to .030.

After the engine starts, choke off ASAP. Then adjust your idle speed up a tad and let it sit for a couple of minutes before pouring the coals to it! After a two minute warm up, your off. Roll on the gas until the engine is good and hot, then whale on it.

These bikes are noted for leaking fuel into the engine just sitting. This would cause your next day plug fouling. Be sure to shut off the fuel, and “tip test” the bike to drain off gas in the carb bowl. Do this when done riding for the day.

  • RSA210

Posted October 06, 2002 - 03:34 PM


Onyxxx,Other items that deserve honorable mention would be: Check and clean air filter-don't over oil it.
I also would clean the carb. real good to eliminate
clogged jets.Take a fuel sample to make sure you
don't have dirt in fuel system/contamination.
As TK mentioned EK plug and always close fuel petcock.
Hope this gives you some help. :)

  • onyxxx

Posted October 06, 2002 - 06:24 PM


Thanks for the info. I was wondering if any of you know how the difference in degrees would make a difference as far as if the bike is running lean or rich. I thought the colder it becomes, the leaner your bike runs? Also I was made aware that this bike comes very rich from the factory, would moving up a clip on my needle cure the cutting in and out when on the throttle in fourth gear, or should I go down on my main jet? I am still puzzeled to the fact that since I removed my air lid and uncorked the exhaust, that my bike would still be running rich, I thought that would lean things up.

  • tk421

Posted October 06, 2002 - 06:43 PM


Onyxxx, yes, the colder it gets the leaner your bike runs. Have you seen Motomans spread sheet for altitude and temperature corrections?

Check it out. :)

  • dominator426

Posted October 06, 2002 - 08:49 PM


The sputtering, backfiring and cutting out are probably caused by a lean condition from uncorking intake and exhaust...Cooler temperatures have made it worse.
Your WR is now just broken in...What elevation are you at? You could try droping the needle clip a notch or 2 and maybe try a 170+ main fuel jet...The BK mod is strongly recomended. It would help avoid plug fouling and improve response too; I've adjusted my accelerator pump at .4 second at about 1/3 throttle, before engine was ever started, and have never fouled my CR8EK.

  • blue_beast_wins

Posted October 07, 2002 - 12:11 AM


high elevation / colder air usually means thinner air wich means you will need less fuel, start leaning brother.

  • dominator426

Posted October 07, 2002 - 11:19 AM


Careful now...At higher elevations, the air is thinner and requires leaner jetting. At colder temperatures, the air contracts and becomes more dense, requiring richer jetting. I don't know what onyxxx's elevation is but he is experiencing a lean condition. Plug fouling may have been caused by excessive accelerator squirt duration...

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  • blue_beast_wins

Posted October 07, 2002 - 06:47 PM


I'm still tipping it's rich :)

  • Dodger

Posted October 08, 2002 - 04:49 AM



Dodger :D :)

  • onyxxx

Posted October 08, 2002 - 09:03 PM


I ride in Michigan. I thought I was running rich because of the plug color until reading posts. I want to jet my bike so that it runs well in spring, summer , fall. Temps vary from 50 to 90 degrees, is this possible. Most of my riding is done in summer.


Posted October 09, 2002 - 07:19 AM


The cooler fall temps can definately have a fouling effect on your plugs. Many of us old timers who have changed things like, removing the ACV, are running a summer jetting setup (Richer) and a winter jetting setup (leaner). When the temps high I can get away with a 48 pilot and a 100 PAJ. but when the morning temps drop into the low 60's, I've got to drop to a 42 Pilot and a 75 PAJ. Otherwise I will foul a plug almost everytime.

Bonzai :)

  • dominator426

Posted October 09, 2002 - 07:13 PM


It surely is no mystery that, at colder temperatures, air contracts, causing air to be denser and increasing the oxygen content per cubic feet...Consequently, more fuel is required to match the extra available oxygen. Therefore, a richer setup may be needed for colder temps...
Gasoline quality may vary around the world, but the good old laws of physics don't. :)

  • blue_beast_wins

Posted October 09, 2002 - 11:25 PM


This is called better vaperisation, not more fuel, a well jetted anything will always produce more horsepower on a cold night thats why they invented water injection.

  • onyxxx

Posted October 10, 2002 - 09:05 AM


The last few days I spent alot of time going through old posts to try and gain a better understanding of how to relate symptoms of bike to what needs to be changed in carb. I think I found out why I fouled my plug the first day I rode. I started it up for a second, then shut it off really quick before it warmed up and did not ride until probably an hour later. It started fine but just ran like hell and after getting back, pulled the plug and it was very black. I read in a post this could cause your bike to foul a plug.

However what I still do not understand is when I put the new plug in the second day and went for a ride, the first 20 minutes it poped and cracked really bad, as time went on the bike started to stop the loud poping and run better. So my question is, because of the colder weather I was running lean and it was poping like crazy, but when it really warmed up it stoped, just wondering why it stoped popiong, temp stayed about the same within that time period. Does the bike run a little more richer as it warms up? Also I am trying to remember if the poping was when I would be off the throttle, because if the throttle was closed and it poped, wouldn't it be the PJ that would need to be richened up or screw turned out?

  • mikeolichney

Posted October 10, 2002 - 11:13 AM


Did you put fresh gas from a different source in as advised above? If not, do that right away. Use race gas to test the problem if you are not sure about gas quality. The alcohol that gets put in the gas for winter pollution reasons causes plug fouling. I did not take this advice and went through hell. See the post "fouled plugs= foul mouth" for details.

  • dominator426

Posted October 10, 2002 - 12:58 PM


Onyxxx, you are right about your pilot jetting in relation to popping during engine braking...Also, I too have noticed it running a bit leaner and not quite right until well warmed up...I actually have to cover a rad with thin cardboard or something (cold front) when temperature is below 50*F. It's also better for the engine to be running at a high enough "operating temperature".


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