2 stroke jetting and mix ratio questions

[03warriorrider]

I just rebuilt a 89 rm125 and I'm having a difficult time getting it jetted. I put in a new wiseco pro light piston and ring(stock bore size), a full fmf pipe, stock replacement boyesen reeds, and twin air filter. It also has no air box lid, not sure if it ever did as when I bought it was a mess, and the exhaust ports have been ported. So far I have it pretty close, it still has a sputter like its rich after about 3/4 throttle. Stock jetting is 55 pilot, 330 main and 3rd clip on the needle. Right now I'm 60 pilot, 310 main, and 4th clip. I'm thinking I still need to adjust the main to maybe a 300? It just seems weird to me that I'm so far from stock jetting and this thing is still stock bore size, again I'm a newb when it comes to jetting so I could be wrong.

For oil I'm running castor 927. One of my questions is what should I be mixing it at?....right now I'm mixing 20:1 because that's what my manual is saying to mix but the oil says between 20:1 and 60:1.

Thanks for any help and I apologize for anything that my scream newb but this is my first 2 stroke and first time jetting something :)

[IcutMetl]

It seems the general consensus for mix ratio on a small 125 is 32:1 or 40:1. Start the jetting right where it ran best last, or with the needle in the middle notch; I've found that on my 250R, the needle position has the biggest effect on jetting over all the other circuits, and the main only really comes into play around 3/4+ throttle. Raise the clip to lean it out, and opposite to richen. Go to www.carbparts.com and search around for their Keihin jetting chart- it was helpful to me; it sounds like you have a Mikuni, but should be the same concept. Also Duncan Racing's website has some very helpful pointers as well.

Good luck!

[mxpimp2000]

32:1 is 4 oz per gallon which is wat i ran wen i had a 2 stroke because it will keep it lubed up good and wont be too much to foul a plug which in some cases it can foul a plug being if u let it sit and idle or lugg it real bad.

when i put a pipe/filter/no box lid/boysen reeds/wiseco piston in i just went up a few sizes on the main jet and it ran good.

[250rAL]

Going to 32:1 should help a lot. With your mods I wouldn't go below the stock main. If anything you should be 2-3 sizes above it.

[KXRida]

Jetting in a sense is trial and error. What works for one person may not work for you. A safe mix is 32:1. Jetting is also about consistency. Pick a ratio, pick an oil, pick a fuel and jet for the conditions. Make small changes at a time and see what works best. Castor 927 is a good protecting oil but will burn dirty unless it's almost jetted spot on. I personally ran either amsoil or Klotz R50. Klotz was by far one of the cleanest best protecting oils I've used. Maxima K2 and Motul 800 aren't half bad oils as well. Go get yourself some jets and do some testing. Keep in mind if you are jetting the bike in winter conditions (not sure where you're from) that you'll have to rejet come spring time.

FYI, most bikes don't come with an airbox lid. Besides some enduro bikes, I've yet to see a bike with an airbox lid.

[03warriorrider]

thanks for the help guys. I'll start mixing 32.1, get some new plugs and keep at it.

KXrida thanks for the FYI I didn't realize that....I'm use to four wheels and this is my first bike. I didn't intend on getting this deep into things, just wanted something to mess around on but one thing leads to another and before I know it im doing a complete rebuild.

[KXRida]

Keep in mind to rejet for your new ratio. Switching ratio's in most cases is a "band-aid" fix and most likely results in the bike running worse. The common mis-conception is that oil fouls the plugs. Infact the gas fouls it, then unburnt oil saturates it. Google spankys jetting guide. It's rather helpful.

[03warriorrider]

thanks, I was aware the the ratio will mess with the jetting as well as the cold weather. I plan to drain all the old mix out and start with with the new mix anyways. That guide is pretty good...pretty similar to the one Ive been looking at actually. Now if it'd only stop raining I could try and get this thing dialed in. t=412662:grr:

here's the guide I found
http://www.thumpertalk.com/forum/showthread.php?