Strange Spark Plug Pattern

[2 stroke forever]

Hi Everyone,

 

So I have been trying to jet my 2002 RM 250 properly, but I have been having issues with a rich condition and fouling plugs. I started out with fmf jetting (pj 48, needle 2nd, main 168). My setup is a first gen. v-force, fmf sst and fmf turbine core. After messing around I went to a  pj 42, needle 2nd, main 158 and as a result the top end sounded clean, starting was easier, but bottom and mid were still rich. After more messing around I decided to put the stock pipe on because I heard many people complain about jetting difficulties with the fmf sst. Once I put the stock pipe on with the same jetting (pj 42, needle 2nd, main 158) the engine sounded great (crisp, more power, clean sound). Now onto the problem. I have been inspecting the spark plug to achieve a chocolate color, but now instead of getting an all black, chocolate or white plug, I am getting a half black, half white plug. What could be causing this? There is no known engine work and no mods have been performed besides those mentioned. I have attached pictures of the spark plug after 15 minutes of use. Please, any advice would be most appreciated. Jetting woes have been killing me!

 

Sorry the pictures are inverted.

Edited December 29, 2014 by 2 stroke forever

[MotoXRyne]

My 07 is/was the same way. The lighter side of the plug is what you want to go by, at least in my case that's how it worked out. I run 100LL fuel and the plug is half dark brown, half tan color. 

Edited December 29, 2014 by MotoXRyne

[Excitable]

optimal the plug should be a tan to dark tan,   go with what moto said

[2 stroke forever]

Here are some clearer photos. One side is completely clean right down to the bottom of the insulator and the other side is black all the way down the insulator.

 

[zig06]

There's a very good chance that your jetting really is spot on.  When you do your jetting runs are you using a new spark plug or at least a clean one after each "run & read"?  Also keep in mind that after a run at say "mid throttle", you need to clutch and kill the motor as quickly as possible "at that throttle setting" to get a good read, riding around at mid throttle and then back to the barn won't do it, plug readings are basically "instant readings" they only tell what you just did (not 5 minutes ago). 

 

It would also be helpful to mark the plug so you know what side of the plug is clean (exhaust or intake, left or right).

[2 stroke forever]

Unfortunately, I am guilty of not using proper edict. This plug was new, but has about 15 minutes of track time ( tight track with no long straights) and then I pulled off just as the engine ran out of fuel.   I will make sure to do a proper test this weekend and report back. Still, it worries me that non uniform combustion could damage the engine, i.e. one side of the piston is much hotter than the other.

[mlatour]

Has the head / combustion chamber ever been machined?

[2 stroke forever]

Not to my knowledge. I am the third owner, but based on the modification and how the head looks. I don't believe it has been altered from stock. Some pictures are below. Let me know what you think. The pictures are when I first bought the bike, so the burn pattern doesn't relate to the current situation.

Edited December 29, 2014 by 2 stroke forever

[JBFL]

Spark timing is a degree or two off. A good portion of unburnt fuel is going out the pipe.

Edited January 1, 2015 by JBFL

[2 stroke forever]

Wow! I will try adjusting that. Thank you very much. That makes a lot of sense! ?

[JBFL]

www.strappe.com\plugs.HTML

Everyone needs to read this if they own a 2 Stroke. Lots of literature from Gordon Jennings out there.

[2 stroke forever]

I haven't been able to find a place to test yet, but I checked the timing and it is pretty spot on. What distance constitutes 1 degree of timing? Would a few millimeters make a significant difference? I think I have a place to test tomorrow, so hopefully the issue will be clearer.

Edited January 2, 2015 by 2 stroke forever

[noaht4]

This doesnt really help you any but how do you check the timing?

[2 stroke forever]

There is a marker on the stator that you line up with a mark on the case. It is preset from the factory.

[JBFL]

The width of the mark is pretty close to on degree. Going within 1\8 inch either way should get you there. Use good fuel if you can get 100 low lead use that. Make sure and do good plug chops for accurate readings.

[2 stroke forever]

You think so? I believe I have a 155, so I will give that a shot. I am at a wash-way right now and about to start her up. There are a lot of no trespassing signs, so I may not be able to do a proper 5th gear plug chop.

Edited January 3, 2015 by 2 stroke forever

[2 stroke forever]

Alright, here are some results.

Procedure: warm up, rev a bit to make sure it keeps clean, engine is hot, take off, semi fast run down the stretch then fast run to mech box, kill engine, pull plug.

-The first plug is a 5th gear run with a 158 main.

-The second is a 155 main. Okay, on the second plug a guy waved me down and apparently the wash I was in is now a protected reserve. That is California for you. So keep in mind the second plug I only had a chance to do a fast run down and then a slow run back. Not a real run, but it is all I have at this point. I will do more tests next time.

Also, just listening to the bike I could hear a marked improvement in throttle response and a cleaner sound when I went from a 42 to 40 pilot. The air screw was about perfect at 2 turns out, which I believe is within the range it needs to be. After putting the 155 in, the bike felt cleaner up top and smoother. The sound was almost electric, if that makes sense. This observation was while I rode it, not while it was on the stand. I will probably be at the track tomorrow, so I will update again.

First Plug

Exhaust

Intake

Second Plug

Exhaust

Intake

Edited January 3, 2015 by 2 stroke forever