RM 250 fouls up spark plugs-need advice

Mar 18, 2004
23
0
Hi all,
My 96 RM 250 has developed a problem where the spark plugs will foul up after riding for just a few minutes (anywhere from 15 to 45 min). The plug gets covered with oil and fouls up.

Initially I suspected I was running too rich a mixture. So I rejeted the carb with a leaner set up (changed the jets to a smaller size) and also changed my fuel mixture to 46:1 (I usually run 40:1)

This didn't seem to help, the bike still fouls up the plugs. It also drips some of that dark gunk out of the tail pipe, although it seems that most bikes do that anyway.

What can I do here to correct the problem? I mean, I don't know what else I can do. The bike is as lean as it can be and this still happens. PS: the bike was running fine during the summer, than one day this started.

Basically when I install a new plug and run the engine a bit, there will be fresh oil/fuel in the threads and it doesn't seem to burn up. I can't tell if this is transmission oil or mainly premix.

Someone suggested that my camshaft seal may be leaking transmission oil into the engine and that replacing the seal should solve the problem. Do you agree with this? Naturally I would want to try a simpler solution before taking the thing apart to replace that seal.

Should I have no alternative but to replace the camshaft seal, how big a job would this be? Could anyone that has done this tell me what's required to do this? Perhaps there is a set of instructions of how to do this online somewhere? I have the Suzuki manual but it doesn't show how to replace the camshaft seal. I'm hoping that there is a better solution, but in the event there isn't, any help would be appreciated. Thanks in advance.
 

overbore

Member
Dec 24, 2001
362
0
I presently have a rm250 which I changed last year,which you just drain
down coolant and oil and tear right side off to get to crank drive gear and
take a impact and get gear off and pull seal out with everything in reverse
to put back together.If it was the seal thou you should see some sign of
oil on your rear fender if you look close or atleast I found after looking closer.
overbore.
 

zookieman

Member
Jul 7, 2003
118
0
The less oil you run in your mixture the more rich you are running. Less oil means more gas. It is not your mixture it is your carburation. Or dirty air filter.
 

mobrown

Member
Jan 26, 2004
198
0
Check Air Filter

It could be that your air filter has an oily substance on it that is getting sucked into the cylinder. Also, what kind of oil are you puttnig on your filter when you clean it? Oil designed specifically for air filters works differently (and better) than using plain ole two stroke oil on it (some people do this).

If your using ATF in your tranny try using regular motor oil (find what kind is specified for your bike) because ATF doesn't burn and will foul your plugs... motor oil will burn (this is no permanent fix of course but you could probably ride without fouling plugs)

If all else is good it is mosly likely oil entering through a seal between the cylinder and tranny somewhere.

Good luck!
 
Mar 18, 2004
23
0
Thanks for the quick reply, guys.

Here's some more info I hope may help:

Running Yamalube 2R for the fuel mixture. Run 92 octane gas, usually 40:1

Running Yamalube 4 stroke 10-30 oil for the tranny (the more expensive stuff than regular oil, which had worked fine for over a year)

As for the air filter, it is clean. I use the K&N oil filter cleaner (the stuff you spray on and rinse off after 10 min). And I cover it nicely with foam filter oil, the blue stuff from Bel Ray. I must admit that my filter is a bit old although it still seems to work fine. I have also been told that the K&N cleaner isn't as good as soaking the filter into gasoline and then washing it with soap. Could it be that my filter is too dirty even after the care I take of it?

On a sidenote, I noticed someone posting (about 4 pages down) a similar problem and a user suggested the problem to be the floaters in his carb. That would be a far easier thing to do rather then replacing the camshaft seal. Anyone agrees with this?

What I didn't mention is that the plug typically fouls after I ride for a while and then shut it off. Upon trying to restart it is when it fouls up the plug. I recall during a race last year when I had to leave the bike idling for a long time as I was afraid to turn it off and miss the race (I was down to my last plug). This kinda goes along with the user I mentioned above said about his bike.

Here's a couple more questions, while at it: what compression should my rm have? The manual only lists a ration, I want to know the psi.
 
Mar 18, 2004
23
0
Here's more info:
for spark plug I'm running NGK br9es. I have tried br8 and it didn't make a difference, it fouled up just as quickly.

And I cannot notice any oil missing from my transmission. Basically the level seems to stay the same, which makes me wonder if the problem isn't with the camshaft seal afterall. And yes, I do get a blackened rear fender where the exaulst is, not to mention that black goo drips from the tip of the pipe onto the swing arm. At times it seems to smoke a bit (the white smoke) but that doesn't seem to be much more than normal.

I have also not cleaned the exhaulst pipe at all in over a year, maybe two. Wonder if this could be a potential problem too?

The info posted by that other user I mentioned in the previous message, along with the replies including the carb floaters, was posted on March 09 with this heading:

98 YZ250 fouls plugs on cold start
souphmars
 

a454elk

Mexicutioner
LIFETIME SPONSOR
Jun 5, 2001
7,538
18
When was the last time you did the top end? Pull off the head and look at the top of the piston and cylinder walls. Maybe oil is splashing up and getting past the rings, not sure but I'm also not sure what the compression is supposed to be. But if you at leasy look at the head area and go even further and pull off the cylinder, you can see how much blow by is going on. I'd go through the carb and make sure all the circuits are clear and the slide is working right. Go to the stock settings and start from there. If you have a stock bike, no pipe, silencer, so on, then staying near stock should work. Also, check the reeds, maybe they are allowing too much past and not working right.

Did any changes occur with your bike since this happened or did it happen all of a sudden after working right? Did you change out something? We'll try and help if we can, there's enough of us here for that!
 

a454elk

Mexicutioner
LIFETIME SPONSOR
Jun 5, 2001
7,538
18
Oh, your exhaust may be gunked up but that shouldn't cause that. Take off the pipe and hang it upside down and let it drain out.
 
Mar 18, 2004
23
0
Thanks, a454elk
More info as requested:
I got the bike 2 years ago and haven't had the topend done yet. Perhaps cause bike was running just fine and had tons of power up to this incident that apparently changed things: I had a nasty head-on collision with another rider.
Didn't think this to be of much importance but the truth is, the bike was running fine up to that day - after this crash is when it started to foul up the plugs. Makes me now think that the problem may be with the floater inside the carb, as the force of the impact could have knocked around a bit - is this plausible? Could the cummulative speed of 50km/h (35miles/h) have caused the flaters to misalign?

I have kept an eye on the transmission oil and it hasn't decreased any more than usual (which typically is none in between changes - once every 20 hours or so). This could mean that the problem may not be with the camshaft seal as suggested by a couple of guys at the track.

I'm tempted to open up my carb and put back the stock jets (since these run fine before) and completely clean the carb and adjust the floater height if need be. Guess at that time I'll take off the head and look inside. If I remove the top cover, can I just put it back right after or must I change the gasket? I'm new to doing maintenance on a 2 stroke bike, so forgive me if some of my questions seem redundant.

PS: since the crash I haven't noticed any loss of power/performance. Only issue seems to be with the fouling of plugs.

And no, I haven't cleaned up my FMF Gold pipe/silencer since I got the bike. Likely needs a baffle replacement at the very least. I believe it is very filthy inside since that black gunk comes out of it. I'll try to find info on how to replace the baffle and get it done asap too.
Thanks guys. Can't wait to get the bike running again, now that our 6 month long winter is almost over.
 

motometal

LIFETIME SPONSOR
Sep 3, 2001
2,682
3
been there, done that. my '96 was a plug fouling mother! Changed from Maxima Super M to el cheapo Suzuki oil and the problem all but went away. I've been told that since then, Maxima changed the formula of Super M?

If the crank seal was leaking significantly, the bike would be blowing mega-smoke!the oil would be sucked into the crankcase on the intake stroke and then would mix with the charge, transfer up above the piston and try to burn.

Could you just go to your dealer and pay them a bit to do a quick compression test? They would have the specs as well. Low compression means inefficient combustion, which can foul plugs.

The float level could cause this. The bike would run blubbery off the bottom, and it would probably spew some gas out of the overflow tubes. You shouldn't see any fuel coming out of the tubes unless the bike is tipped quite a ways down. If it comes out when you just barely tip it, the level may be too high. Careful here, too low of a float level could be worse...the bike could starve for fuel when it needs it the most (wide open).

How fresh is your fuel? Did the bike sit a while after your collision? If the fuel can't efficiently combust because it's stale, there will be increased spooge and possibly fouled plugs. Conversely, fresh race fuel can help keep things clean.

It won't help much to clean the exhaust out now, I would wait until after your problem is resolved and clean it then...that way it will stay clean.
 

a454elk

Mexicutioner
LIFETIME SPONSOR
Jun 5, 2001
7,538
18
If you are careful, you can pull off the head without messing up the gasket, it should be a rubber O ring type and if it stays in the channel, it will be ok. If it comes out, it takes an act of God to get that one to go back in. The head, if you are not sure, is just the top portion of the engine that the plug goes into. Not sure if I was clear or if you already knew that. Make sure your exhaust valve is working right while you're in there too. I doubt it would be a float problem, like Metal said, you'd have gas pouring out just sitting there. Clean out your power valve as well too, it may have gotten gunked up as well. wouldn't change your jetting as of yet, if nothing was done and it worked fine before, that ain't it.
If your carb is gummed up, you'd have ppower issues as well as it not even running right. Blow through your air passages and make sure they are clear too.

Keep us updated, good luck.
 

cr80 kid

Member
Mar 15, 2004
12
0
You should try running the recommended 32:1 works great for my neighbors RM 250. Also you should start giving it a lot of revving when you shift(while holding in the clutch) it worked for me and my CR 80. I foulded up plugs because i had to clean it out. Hope this helps :clue:
 
Mar 18, 2004
23
0
Here's an update at my fouling problems:

Took the bike to the track today and it didn't foul a plug, in fact it run great.

The problem, as it seems was with the floats inside the carb.
Someone here had suggested this to be the problem and I gave it a shot. However I was unable to properly adjust it. A friend did it for me and I took the bike to the track today. It run strong and well, never did foul the plug and it wasn't covered in dark liquid like before. It had some minor amounts of wetness but not much (running motul 800 at 50:1). So it seems that my problem with annoying fouling has been solved. I urge you to have your floats adjusted before spending any money with some mechanic that will charge you a small fortune trying to diagnose the problem. I tried to set mine to 16 mm, which seems the norm for many carbs - but could not figure out the proper way to do this and even though I thought I had it right, it wasn't. So be sure to first try the float inside the carb. Get someone to do it if you must. To save money, bring your carb to a shop and have the mechanic adjust the floats ONLY - do not let them do any other work on it as it could be mean a waste of money.

I am really pleased to have my bike back without having to go through a seal replacement, which was looking to be what I needed. I will be taking the bike to track again tomorrow and my fingers crossed that the plug will hold up.

Should this (the floats) be the problem I would hope that the message gets out that this is something most people having issues with fouling would be aware of. As is this seems to be a 'hidden' problem and few seem to know the answer.
It is thanks to this forum that I got the bottom of this. This place rocks. Thanks all of you who took the time to share your experiences with us. You got me on the track again, and back on track :)
 
Top Bottom