hi I don't know if any one can help but a friend has a montesa 315 r (01) which goes through a spark plug every 2 trials. some one said maybe run a hotter plug but was wondering if anyone new of this fault. cheers Ian.

what is happening to the plug? oil fouled? how does it run? is he running the proper heat range? a B6ES or G or IVX? the exhaust may be pluged up causing it to run rich, may be his riding style, what ratio mix is he running? is it a quality oil? is the bike jetted properly? did this just start or did he just get the bike? does it have a clean air filter? maybe it's loading up, need to keep it cleared out....

my 315 only needed a plug abought 2 times per year running 3.5 oz per gallon (36:1 ratio) using maxima oil

Mine used to foul the plug regularly until I got the exhaust midbox repacked.

Edit: that was after I had tried all the common things, carb settings, fuel mixture, plug type etc.

Edited August 25, 201016 yr by tt5th

are you using a resistor R TYPE plug?

I assume by "eating plugs" you mean that the plugs get fouled? I run 80:1 oil:gas mixture, and I have an iridium plug. I've also taken the trouble to jet my carb pretty well. I've been on the same plug for the last 3 years.

First suspect is the carb jetting. Second suspect is ignition misfire. Also worth checking are the reeds and crankcase seals, which can be determined with a leakdown tester.

BTW, 36:1 is too much oil in my opinion. This kind of ratio is used for MX racing when the engine is WFO most of the time. For trials riding this much oil will end up in the crankcase. Furthermore, this much oil actually makes your fuel:air ratio too lean, so if you insist on mixing 36:1 then you need to compensate with richer jetting.

BTW, 36:1 is too much oil in my opinion. This kind of ratio is used for MX racing when the engine is WFO most of the time. For trials riding this much oil will end up in the crankcase. Furthermore, this much oil actually makes your fuel:air ratio too lean, so if you insist on mixing 36:1 then you need to compensate with richer jetting.

I know, ...most trials riders and engineers agree with the factory recomended 80:1 ratio, but I am a mechanic, I am the guy that fixes the engineers screwups, I would not recomend this kind of oil ratio to a novice rider, you need to know what you are doing if you are going to run that much oil.

I have been running this oil mix (32:1 to 40:1) with maxima 927 for abought 12 years, yes it does require slightly richer jetting. I ran the same piston, rings & cylinder for 5 years straight with no measurable wear, my friends using the same bike were going through a piston every year with 80:1 straight synthetic.

I am old school, some of my methods and theroys are due to my upbringing and education. oil is good, more oil is better, more oil = less friction = more power. more oil = better engine longevity.