Odd plug fouling

[wirefryer#85]

Hi guys!

Been out a bit on my "new" RM and ran into a fun new problem.

Went to Chadwick ORV area in Missouri over Labor day wknd with two other loons on new bikes. (lucky *******s!)

My 1981 Rm 250 ( restored this spring and summer) fouled 7 NGK B8ES plugs and one NGK BR8EG while consuming just over 9 gallons of premium at 50:1 with Yamalube 2 R over two and a half days of riding. The 'Race Plug' did best at half a day.


I've had this bike since 1990, restored it once before and raced it for many years and have had every single piece of it in my hands, twice!

Before this rebuild, I could run all day on one plug if the initial fire-up didn't fuel-foul it, if I got into alot of poking along waiting for someone or doing a downhill the engine would hack and sputter a bit until I wrung the snot out of it then it was happy again.

Now it doesn't sputter at all. It'll either die in camp or lose about 10 hp all thru the RPM band while at speed, mostly on the top, just hits a wall.

I'm starting to think coil or stator but I like some input from the rest of you guy's.

Engine: 3rd oversize on the cylinder, 2 races and 2 play wknds on it, still has really good compression. Has sat for 2 years out of frame. No white smoke or air leak indicators.

Air filters: K&N on both sides, nice and clean.

Ignition: factory stator, replaced in '95' after a wallered out main bearing problem. Coil is factory from my parts bike, decent spark.

Carb: Mikuni 38mm Round Slide. Fully cooked and blown out with NEW jets, floats, needle and seat, ect.

Before the rebuild, it loved a 45 pilot and a 280 main,(320 is stock) needle is stock, at the second clip up and got a nice tan on the NGK B8ES plug.

While in Missouri I dropped to a 40 pilot and went to the highest clip on the needle w/280 main and got a black insulator and electrode while the rim of the plug remained clean. Elevation was a tic higher than Kansas but couldn't warrant the drastic fouling problem.

Reeds: Brand new Boysen 2-stage power reeds.

Weather: Low humidity, 70-85 degrees, nice! (unless we stopped and sweated a bit whilst I swapped a plug :bang: )

Exhaust: 'Cleaned out with cable' factory pipe, no dents, and New DG Shorty silencer, sealed on all joints, smoked and drooled well.

No odd noises or other weirdness.

Anyone ran into this??
All help will be appreciated :)

Thanks!
Tim

 

[jason33]

could be burning crank case oil,mabe a bent crank- mine was bent verry little but it was enough for oil to get past the seal- bad seal,or center case gasket leaking ,my kx did the same stuff-i used yamabond (crapp) and it leaked through the center cases,check the oil level.
i ended up making a gesket from a roll of material, either liquid or paper they all need a good seal,your bike should rip! espescially with 50:1 - is the plug oily, carbon fouled ,sooty? im assuming its oily

 

[wirefryer#85]

Jason,

I took it to a race in Missouri a while back, ran the practice loop just fine. When I got on the starting line it just would not fire.

Checked the coil and stator with a multi-meter and the coil was weak and the stator was dead.

Replaced both and now have good spark but the timing is way wrong, all it does is backfire or not start, depending on how I wire up the stator. Tried another ign. box with same results.

Now I suspect the flywheel key may have broke and allowed the timing to change, I'm still on the mend from a badly broken clavicle :( but I'll get the flywheel off to check it soon.

Thanks!
Tim