I have rebuilt my 123 and it starts and runs fine but there is black oily residue leaking from the exhaust. Is this a jetting problem?

Cheers

John

Sounds like its running too rich (jetting) or too much Oil to fuel, what mix are you running?

Your petrol to oil ratio should be 25:1 (40cc oil to l litre petrol). Use standard mineral oil like Gulf 2T or Oregon 2T semi synthetic which meets the latest JASO FD specifications for clean running. Don't use fully sunthtic at lean (greater than 25:1) ratios.

Plug colour, the porcelain centre electrode insulator should be a pale chocholate brown and dry, if not check timing then correct the jetting. If plug is OK and you are using above fuel mix just ignore oil from exhaust, means your engine is well lubed, better than too little lube.

Cheers

Did you clean the exhaust out when you rebuilt it, if not it could have years of oil built up in it. Run a gas torch through it to burn it out, this could take about 20mins. Mix your oil/petrol at about 75:1, if you mix it at 50:1 or 25:1 you certainly will have oil coming out of your exhaust, you don't need that much oil. If you rebuilt the engine you could have damaged the crank seal on the clutch side, gearbox oil will be sucked into the bottom of the crank and be pushed out your exhaust.

I don't recomend 75:1 in a vintage bike, the least amount of oil should be 50:1 in my oppinion, I run all my bikes at around 36:1 and have no problem with spooge (slang term for the black oily stuff) as long as my bikes are properly jetted and I am using good quality 2-cycle mix, you say it runs good, so probably not jetting, if your crank seal is bugered I think it would be pouring out rather than just a residue. good chance it's just cooking out the old oil in the pipe, take it out and open it up for a few miles to blow it out, that should create enough heat to burn out most of the old oil, if it is an oily pipe it will start smoking a lot as the pipe gets hot, then it will start to clear up, also

use good oil

Hi Ive run my Montesa 248 at 50:1 with no problems modern oils are far better than when the bike were made, so you dont need 25:1