I've gone through 2 plugs in less than 4 hours of riding recently. The arc short circuits from the center electrode to the side of the plug instead of across the gap. The symptom was that the bike would start but as soon as I opened the throttle, it smoke a lot and die. I could clean the plug with a wire brush and the bike would start and run again until I revved it. I put a new plug in there and everything is great. I don't know of the insulator is cracking or if it is carbon tracked. I'm running a NGK BR9EIX. The local shops are always out of the copper plugs and at $10 a pop for the iridiums, I don't want to be replacing these things too often.
Spark Plug Problems
- Thread starter 76GMC1500
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steve.emma
Member
- Oct 21, 2002
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hi, apart from the fact your jetting could be out or that your premix ratio could have to much oil (try 40:1), your plug is too cold. try a number 8 or even a 7 plug and see how it goes.
p.s. you didnt say but im asuming you are talking bout the cr250?
p.s. you didnt say but im asuming you are talking bout the cr250?
If you are sucking trans oil,you will get the plank! Need more imfo,you know that.
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- #4
I was sucking trans oil, I replaced the seal but hadn't changed the plug yet. I took the bike out to Carnegie this weekend with a new plug and ran it for 6 hours (and still runs). The bike ran perfect and made a ton of power. Maybe the aluminum was making deposits on the plug that were causing it to arc off the side of the electrode.
The seal went bad for a reason and you "worked" around it,now are you going to split the cases? The seals and bearings can hold all sorts of surprises if not proprely taken care of,and once in a while a "work"around works!
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- #8
This picture of the underside of the crown is the reason I don't run a hotter plug. Honda recommends the 9, in 40 hours of riding I never fouled a plug. Only recently I have began having problems. The bike does load up on the tightest single track trails, but a quick rev clears everything out. The tracks and trails I run have some 5th gear straights, so I'd rather error on the side of cold and risk fouling a plug vs. burning a piston. The 87 CR250's had higher compression ratios than most newer bikes (9.1:1), the combustion temps are a little hoter.
I love this "work around" for a roached engine,bad air filter,carb,reeds or timing,put a br8eg in,you do not need any top end,it will just blow anyways because of the underlying problem! GM,need more imfo,compression,what did you do to the bore,either too much mix,or not atomizing properly for a couple different reasonsflattie said:
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- #10
I don't understand, am I trying to work around a problem or is using the BR8 instead of the BR9 working around a problem? I couldn't ask the bike to run any better than it is. It pulls with just about everything on the track (except this one 125 it barely stayed ahead of). It's got excellent throttle response, had never fouled a plug (over a wide range of conditions and elevations), starts easily, loads up a little in the technical stuff. It just had this weird batch of problems. They were probably all attributed to the bad right crankcase seal. Everything is better, now. I was just looking for some other ideas or confirmation.
steve.emma
Member
- Oct 21, 2002
- 285
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just a couple of points to clear up... the heat rating of a plug has no effect on the temps that the engine will run at. the plug heat range only affects the temp of the plug electrode and insulator.
you are right that the burnt marks on the piston underside suggest hot running, but this is probably due to too lean a main jet or some other problem causing a lean mixture and or excessive hot running. trust me that a 8 plug would be correct for your bike. but if the bike loads up at some points in the low rpm range it probably just needs jetting.
you are right that the burnt marks on the piston underside suggest hot running, but this is probably due to too lean a main jet or some other problem causing a lean mixture and or excessive hot running. trust me that a 8 plug would be correct for your bike. but if the bike loads up at some points in the low rpm range it probably just needs jetting.
Check the compression,timing(look at the plug),reeds,jet! And,I am a new subscriber to replacing the float valve set every couple of years,how is the slide?
I would try to drop down about 2 pilot jet sizes my new 07 yz250 was eating plugs also, and I went down on the pilot, now it feels like it picked up some horses, havent fouled a plug since. The pilot works from zero to 1/4 turn of the throttle, but it is also meters fuel through the entire fuel delivery range.