conking out

[Feed Your Head]

Twice now my PX125 has conked out whilst decending a steep hill. Both times it took a short while before it would start again. Second time i checked the Spark Plug and it had a thin carbon deposite which i carefully removed with a small piece of emery and then wiped with a cloth, after which it worked fine. In the book it says this deposit is a sign of too rich a fuel/air mixture or a dirty filter (which i don't think is the case as it was only serviced and had filter changed 4 months ago). can anyone explain the fuel/air mixture thing to a not so mechanically trained person like me and, any ideas how to combat the conking out problem?
cheers
Eltjo

[dto79px]

never had any problems with whiskers of carbon on a spark plug for years

is the spark plug the correct grade/type ?

can be caused by cheap 2-stroke oil or to much oil if premix used

use a good quality semi-sythetic or even better a fully sythetic 2-stroke oil

is the bike standard or has it had some tuning bits on it , ie exhaust , jets , kits etc if you can post more details of bike

[Feed Your Head]

Bog standard px 125 disc engine. same for exhaust. the spark plug fitted is a nkgBR7HS ( something in my head thinks this ain't right, but then what do i know??). Filter looks clean. didn't conk out today anyways but still, better get some ideas and advice.

[dto79px]

i have the spark plug as being B6HS which would be slightly hotter plug !!

new px disc engine must be 100% fully synthetic 2-stroke oil used

[Feed Your Head]

yep...use only synth oil. i thought the number of the plug was possibly different. thanks for that dto79px. would've thought the mechanics at the garage would have put in the right one

[Feed Your Head]

quote author=toppy board=general thread=1184504885 post=1184505534]Cross Reference Guide.
NGK B9ES – Champion N2C - Bosch W3C
NGK B8ES – Champion N3C - Bosch W4C
NGK B7ES – Champion N4C - Bosch W5C
NGK B6ES – Champion N5C - Bosch W7C

NGK B9HS – Champion L77C - Bosch W2A
NGK B8HS – Champion L78C - Bosch W3A
NGK B7HS – Champion L82C - Bosch W5A
NGK B6HS – Champion L86C - Bosch W7A

just found this on a previous thread.
handbook of mine says that to use champion L82c

[Ironduke]

does this only happen going downhill? Sometimes when going down hill you pull the throttle fully back and as this cuts fuel off to the engine it relies on the idle jet in the carb to tick over until you open the throttle again. I this is the case I would look at the jet and clean it out .
The carb has two jets, one for providing fuel at idle speeds and the main jet for higher speeds.
The spark plug quoted is ok, you should expect deposits on the end of it, a chocolate brown colour is considered ideal as this indicates the mixture of fuel/air/oil is correct. Too much oil would leave an oily black deposit on the plug, too little would be whitey grey, indicating to little lubrication. with too little lubrication you can get a 'heat seize' where the engine cuts out and the engine will lock up unless you pull the clutch in. Remember, when running in a motor and going downhill, you are advised to open the throttle with the clutch in so that you feed the engine with oil to lubricate it.

Hope this helps

[Feed Your Head]

Thank for that Iron duke. Hasn't happened again since i replaced the spark plug. I think your initial explaination might have been the cause, but the scoot is ticking over and running nicely as ever. might have been, as pointed out, possible sloppy control by me re the throttle. anyways, hopefully it won't do it again.
cheers
safe riding