Advice Wanted - Engine Problems

[Swin]

Hi, can anyone help? KH250 been running great. Now, it seems to be going onto 2 cylinders - done the usual things, new spark plugs, carb set up, and timings. The bike seems to have excessive smoke at high revs and seems to be using the gearbox oil. Would this be; crank shaft seals or piston rings or something else entirely? Has anyone got any ideas before I set it on fire?? Cheers

[kas750]

These things smoke like a drunken Glaswegian so that's not necessarily cause for concern.
Is it definitely using gear oil and can you trace the fault to a particular cylinder?

[Wolfie]

If there is no puddle underneath the engine then the RHS crank seal is about the only other place that gearbox oil can go (unless the casing is broken/porus) and the RHS cylinder smokes as it burns it.

[Swin]

I cant find any leaks but there are oil streaks down all 3 exhaust down pipes. If I clean the spark plugs it will run good for a couple of miles and then it seems to go on 2 cylinders. The bike was running great until last week I took it down a long duel carriage way gave it everything got into 5th gear doing about 70mph then the power started to drop off. I pulled over then it started to rev ok. I set off again and it did the same thing. I managed to ride it home approx. 30 miles. Was ok pottering back home but now it will only go a few miles and I have to clean the plugs again. The plugs seem to be wet but no petrol smell.
P.S. I've owned four KH's and when I say it's 'smoking' I've never had one that has smoked this bad. It's only done 13000 miles, this bike had been stood for 12yrs before I rescued it. Had the carbs cleaned and set up, all the points and the timing done and the tank cleaned too. After all this it ran like a dream. Now, I've got these problems.

[El Presidente]

Whats the chances that something could have got sucked into the airbox intake? Had a similar situation a few Years back when my flasher unit got sucked into my H2 inbox trumpet

[TallyB]

Check your petrol tap as you said the bike has stood for 12 years.
Had a similar problem with a car years ago. Driving around town it ran ok, but going quicker on open roads it lost power and stopped. Found an air bubble in the fuel line not allowing the carb to fill up quick enough.

[oldman]

Check air is getting into the tank when your running

[JA - Moo]

40 year old crank seals, and sitting for 12 years is a bad combo. Your seals are "probably shot". A vacuum/pressure test would tell the tail. But to be real they will fail sooner or later, even if they do test good. Bad seals or going bad seals will cause all sorts of tuning problems. The amount of original miles is moot after 40 years.......