I have a 1988 KDX 200 thats in great shape. I friend of mine who knows a lot about bikes told me to run 40 to 1 instead of 32 to 1.
I use Mobil 1 2-stroke full synthetic premix oil.
Will I be safe at 40 to 1?
Most of the time people run mixtures with less oil to gas ratio is because the riding they are doing. If you are doing slow trails and not getting on the pipe or in the higher rev range, a 40:1 mix is OK. Some people have oils that mix 100:1 but I don't buy that game. Some also mix less oil in so they get more gas in their tank, which takes them about 3 miles further. Because I am mostly on the pipe and and in the upper rev limits of the bike I run at 28:1. If I was going to do nasty trails I too would change to 40:1. Just ensure your jetting is on. Most plug fouls, spooge from the exhaust, and poor performance are from improper jetting. Some people just don't mess with the jetting and change their ratio. This does change some things but ignores a bigger problem and sells themselves short on performance. Lots of info on Jetting in CDkdx forum.
I have found all synthetic does great at 40 to 1. Ratio mix is not the real question--set it and forget it. Then the hard part is working on your jetting. Lots of threads here, but every bike is different, and jetting is a do it yourself job. It has taken me a long time to get mine right, but you really know it when you get there!
I believe the optimum fuel/oil mixture depends on engine RPM, with the higher RPM engines 80 and 125 bikes needing more oil and 250 and up needing less. Now this was based on MX bikes so a KDX is defiantly in the lower RPM range comparatively. If you seach on this topic I believe that you will find a lot of info.
Yes, I've read a lot of great info on jetting from the guys here. My next step is rejetting. It's just very hard for me to find a long straight away where I can go WOT for 20 to 30 seconds in 4th gear. Might have to do it along the train tracks. Will the loose railroad rocks cause any issues with the plug reading.
I rode tight trials last weekend for about an hour. When I checked the plug (brand new before ride) it was light black with a little dry carbon on it. I know this dosen't tell me much because I need to do the WOT plug chop. Maybe this weekend.
interesting phenom with different mixtures, oil weighs more than gas, decrease the oil ratio and you decrease the weight of the fuel.... this has a direct relationship to how much volume the vacuum will pull through the jets, lighter fuel means the vacuum will draw more,.. giving richer conditions..
so if you decrease the oil, more fuel goes into the motor....
now a tertiary effect...
the more fuel that goes now has a higher ratio of fuel to oil resulting in even richer conditions, ...
remember its fuel to air, .. NOT fuel+oil to air
(i had to learn all this roadracing 2-stroke triples)