Why the @*%# do I keep fouling plugs???

[drhill]

I'm getting a bit frustrated with my 83 250r...I can't stop fouling plugs! Fresh top end and it runs great! Dry, sooty, very dark brown usually stops running well before the plug gets all the way black...I've gone up and down with pilot and main jet, thought it was pilot jetting - it wasn't. Looked at the spark today - nice blue/purple spark. Any ideas? Runs great on a fresh plug...not so hot once the plug cruds up...

The best overall jetting has been 48/132 (but I need to go a step richer on the main) FYI...use 32:1 fuel mix. Air filter is pristine Uni...only other mod is old aftermarket silencer.

I ride it pretty hard most of the time. But I've experimented with putting around. Followed the strict recommended break in proceedure.

I use BR8ES NGK plugs...should I be using the resistor plugs?


Thanks for the help!

[4cfed]

resistor dont mean anything just means if you listen to the radio well riding you mave have engine noise threw your speakers lol!!!

132 main?? wow my 82 must have been way over fueled, i ran a 170 main in winter

figuring properly jetted, what pre mix ratio are you running? and what kind of oil? also are you just putting around or are you riding it like a2 stroke should be rode?

[drhill]

Thanks 4cfed - all that info is in the post...oops except type of oil...Maxima Super M

[4cfed]

i read it before you edited it, lol... at first i was thinking maybe mixed to fat, but your at 32:1 with a good oil, so id eleminate that, and you said you ride it hard for the most part, my 82 would foul plugs in about 8 minutes give or take if i putted, and never fouled a plug when i rode it like it owes me back rent.
good filter, good clean carb, 'properly jetted' good oil, good ratio, good riding habits, hmm that about covers the typical problems for fouling plugs,.. im kinda stumped

[jeswinehart]

Dry, sooty, very dark brown

Normally a sign of weak ignition. I know you said it has fat blue spark but I am just going by the several ways of reading spark plugs and that condition is normally indicative of a weak spark.
You did not mention playing around with different clip settings on the needle jet. That was my main trouble on a 2 stroke i ride, but there again the plug had wet black carbon,,, not dry.

[drhill]

You may be on to something with the spark...I have been gapping plugs at .030...if I tightened the gap up would it crutch a weak spark and maybe lead me in the right direction?

The spark wasn't what I'd call "fat" but it was pretty bright...

If the spark is weak is that just a coil issue?

[4cfed]

weak spark could be a bad wire, weak coil, bad/weak ground,

[drhill]

I will say that this is my first 2 stroke and I"m still pretty green at diagnosing these bikes...Like - I don't really know what a good spark looks like...

I guess I'll run through the shop manual recommendations for checking the electrical system parts...

[EarlyBronocGuy]

Make sure you're running the right plug that's called for in the service manual. Put in a brand new, properly gapped plug. If you still have problems fouling that plug, try one heat range hotter.

[drhill]

thaks BroncoGuy...I am running specific plug called for in shop manual and I did gap them to spec...what's one hotter than b8es? B7?? I haven't seen anyone else do this (hotter plug) so I'm a little nervous about trying it and harming something? Or is that not an issue?

[BGP]

I second the comment about the needle clip position. Also, on something that old, pull the needle jet out and inspect the orifice to make sure it's still round and not pitted to death so the needle actually meters fuel correctly. Lastly, RIDE the thing! Putting around and never getting it hot enough will foul it in a hurry.

[Thorpe]

You can also go a half a heat range in plugs... If stock is a B8ES, I full range hotter is a B7ES, But a halfway plug would be a B7ESL

http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf

[Xpress]

It shouldn't foul even if you're just cruising around off the pipe. My T3 doesn't even hint at fouling when I'm just cruising around, even for a long-ish period of time (15-20 mins).

You might also want to do a plug check,where you put a brand spankin new plug in it, then run it full throttle for 5 seconds or so, kill it, then pull the plug, and that will tell you how it's running. (at least I think that's how you do it, I'm still a bit new to pingers too lol).

[bigbadktm]

pretty sure you have to be riding full throttle then kill it and pull the plug, thats how I have always done it..

in my 83 i used to run a br8es with no problems of fouling, not sure what the difference between the plugs is though

[cr480r]

gap plug at .020" for starters.. does the bike run clean while its running? or is it raspy and smokey in the lower gears? Has it always done this? or did it start after some other changes?

[drhill]

Thanks for the input guys. I just gapped down the plug in it to .020...today I'm also going to try the electrical system checks.

To answer questions - I have done plug chops...if anything it's a little lean right now at WOT (light grey/tan at the base of the plug porcelin). It is not smokey or raspy...on a fresh plug it's crisp at all rpm's. just smokes a litte on startup they runs pretty clean. the bike just had a top end w wiseco pistion and rings a few months ago, before that I only rode it one time after buying it and it burnt a hole in the piston..previous owner claimed he cleaned out the carb but I found otherwise.

[cr480r]

well main jets usually have very little to do with fouled plugs.. most plug fouling is done on the pilot and transition to the needle... if the tuning is not the culprit i would suspect a weak ignition..

[4cylinders]

hey, think outside the box. what's your altitude? buy some other brand of plug. suzukis like ngk, hondas like champion. mine run better at 30 than 24. check your exhaust for any restriction. clean the exhaust port. try a different brand of oil in the fuel. and drain the trans oil, check it for contamination, fuel etc. replace it with good stuff, not cheap.

[Xfile]

I had an 84 R that had the same problem....whoever owned it before me moved the needle jet clip but did not re-install the metal retainer that keeps the needle at the bottom of the slide. When you hit the gas it ran fine, but when you backed off the throttle the needle would push up inside the slide instead of going into the carburetor (needle jet) like it should. It fouled plugs constantly until I found the problem.....after I fixed it, it was fine from then on...

[rray62]

Have you checked the reed valve? And how bad is it smoking? Could be the crank seal on the transmission side, maybe???

[drhill]

the reeds were in very good shape when I had it apart 2 months ago...I could check again? I actually just changed the trans oil and put in expensive moto stuff. I'll look at the needle clip and inspect the needle....again that looked good when I had it apart. I'll check out the items 4cylinders mentioned as well...but I just had most of the bike apart for the top end and nothing was obviously bad...

I tried different plugs last night and noticed that some of my older plugs had a noticably stringer spark than one of my brand new plugs? It that strange? The older two I checked were almost twice as bright of a spark...??

[Philaminoooo]

2 strokes are made to be run like an old whore! Stay on it! You'll get used to it, bud. I got an 84 a few yrs ago and fouled a plug the 1st day I rode it over a mile! lol I've been ridin em since they came out & it cracked me up!

[hang&rattle]

This is an older thread but did you figure it out? Have you tried an Iridium plug? They last a bit longer and don't really fowl up. Also make a noticable improvement in smoothness and response. And I get black sooty plugs in my kids 4 strokes, an engine builder told me to go with a 7 instead of an 8 too, just like on the previous page.