keep killin spark plugs

[h125mx]

i dunno wats wrong with my bike. i was riding with my buddies and when we where half way down the trails my bike just starts putting like it doesn't have any gas in it or something....just bogs out completely. so i luckily have 2 plugs with me and so i just changed the plug to see if thats the problem,.....long and behold, starts up on one kick....ride for about 30 mins and it just started to happen again. putting and bogging.....changed it, runs great again.

so my question is,........what can i do or wat should i do to stop fouling plugs?

 

[FruDaddy]

Fix the jetting. You could be using the wrong plug for your style of riding, trail riding (or any riding where you are not WOT a lot) sometimes requires a hotter plug. Most 125's call for a 9 heat range, but if you spend most of your time at half throttle then you may be better served with an 8. Of course a properly jetted bike doesn't foul as many plugs as a poorly jetted one. For more information on plug heat ranges, look here:
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqheatrange.asp?mode=nml
and here:
http://www.ngksparkplugs.com/tech_support/spark_plugs/index.asp?mode=nml
You should read (and understand) the second link before deciding to use a different plug to fix your problem, the plug should be correct for your riding, and more importantly the engines operating temperature when you ride, but changing the plug will never cure poor jetting.

Changing you pre-mix ratio won't fix it either, although many people seem to believe otherwise.

 

[chiro972]

The other possibility is the right side crank seal leaking. My RM250 fouls plugs just like that and the jetting is actually a bit on the lean side. The right side seal when bad allows oil from the transmission to enter the crankcase and get burned and foul the plugs.

Check the jetting first, but if it's OK look to the seal. Also if you are having to add oil to the tranny to keep the level up, that is a good indication your crank seal is shot.

 

[dirtbikingdad]

......Changing you pre-mix ratio won't fix it either, although many people seem to believe otherwise.

I do agree that if the bike has just recently started fouling plugs that a seal could be bad, however, my bike never fouled plugs when the previous owner(s) ran 50:1 ratio. I switched the bike to 32:1 and it instantly fouled a plug after a few rides. Went back to 40:1 and also did some jetting and it has not fouled a plug since.

BTW, I went to 40:1 so I could share fuel with our 65... I felt that 50:1 for that bike was a bit "lean" on oil.

 

[chiro972]

Just understand that as you go down on oil you actually richen the mixture and as you go up on oil you lean the mixture. You may have to adjust jetting accordingly. I do know that a bike that is properly jetted for 32:1 or even 20:1 should not foul plugs unless there is some other mechanical reason.

 

[h125mx]

im new to the whole jetting thing.....is there a pic or something i can see where to change it? i have a 02 cr125. how do you know where to put the jetting setting at?

 

[h125mx]

im also running nkg 9 spark plugs

 

[h125mx]

whats the first thing i should do?
change the spark plug from a 9 to a 8?

 

[FruDaddy]

The first thing that you should do is search for jetting tips on this board, there is a smorgasboard, but it goes way back. Unfortunately, somebody asks about jetting at least three times a week. Again, don't think that changing the plug will fix things, if you don't push the engine much, then the 8 may be appropriate for you. Personally, I run a 7 plug, because an 8 only lasts an hour or so while the last 7 I used lasted over a year. I rev hard for short bursts, but spend most of my time in the mid range.

Dirtbikingdad, you are correct, pick a ratio and jet for it. Personally, I use BP93 octane pump and Motul 800 at 40:1 in both my 250 and my son's 65 (ran great for 1.5 years before I changed the piston as preventative maintenance, the piston still looked good to me). That ratio is consistent, and any changes are with jetting. Chiro is right, you change the ratio, which changed the fuel mix, you added more oil and reduced the amount of fuel. You may have even had the problem of introducing too much oil for a clean burn. 32:1 would have been OK if the bike was jetted for it, but I wouldn't run 32 with synthetic oils. Some synthetics are designed to work at 50:1, the previous owner may have been right. As long as you are well jetted, 40:1 is good too, and lubricates better.

 

[76GMC1500]

These are the exact symptoms of a bad right side crankcase seal. It is not jetting.

 

[Jeromeo]

check the crank seal. In my 125 i run a NGK BR8ES plug. I kept fouling on plugs with the 9's. I need to change my crank seal as well. Check to see if you are losing tranny oil.

 

[2strokerfun]

There is one other possible--but not likely--cause for this. I fought this problem for a long time. Split cases to change seals twice, rejetted continuously. In the end, it was caused by a worn out choke plunger that wouldn't completely shut off the choke circuit when depressed. But it was a 31-year-old choke plunger, so I guess it could be forgiven for being worn.