I have a 2004 Cagiva Raptor 125 and for the last week it's been letting out smoke a bit too hard:

I have had the bike for a year and a half now. I did an engine rebuild as soon as I got it because the cylinder was all messed up (just like the piston, rings, etc) and used the same kind of oil during this period (Motul 2t 710).

It used to produce much smoke when the engine was cold but stop doing it after 1 minute of riding (and rarely producing visible "clouds" of smoke), but now it produces smoke even when hot. I rode it for 30 km yesterday and when I got home and put it in neutral it kept producing visible amounts of smoke when I was revving it. Also, it struggles to idle (only when hot). It starts up very easily when cold and idles just fine. Generally, it rides normal and I did not notice decreased performance.

The oil pump setting is normal.

What could be the problem? I really don't feel like it's the engine again since it starts up so nice and easy (and it idles well when cold). Also when the engine is already warmed up I need to give it a bit of gas in order to start it (i don't need to do this when the engine is cold).

I feel like the carburetor needs a bit of cleaning/ adjusting.

  • So, clean the air filter and carburettor and re-adjust then see how it behaves, as you suggested.
    – Solar Mike
    Commented Sep 12, 2017 at 10:50
  • you should monitor oil & gas usage and verify the ratio is reasonable, but my guess is you have a fuel mixture problem.
    – agentp
    Commented Sep 12, 2017 at 15:09
  • One of two things are happening: too much oil is being injected; oil is bypassing the oil control rings. The first is a carb issue, I'd assume. If the oil injection system is run through the carb, and the carb is having issues, you're dumping too much oil through and burning copious amounts. If the oil rings aren't controlling the oil as it should be, this means your rebuild didn't take as you'd suspected (Maybe too much ring gap? Maybe one of the oil control rings busted?) Just thinking out loud. Commented Sep 12, 2017 at 21:05
  • There's little to no oil control for this model... the oil pump has a little shaft that rotates proportionally to the crank rotations and the carb has no fins that control the oil flow. Also it is a 2 stroke so there's no oil ring on the piston... it just burns through everything Commented Sep 12, 2017 at 21:13

2 Answers 2


The Cagiva Raptor 125 and most two strokes motorcycle engines have a crankshaft oil seal. These keeps oil out of the crankcase and where it belongs, usually in the transmission.

It's possible for this seal to leak. The two stroke engine just burns the oil that leaks in, so the vehicle tends to operate fine for a while. Eventually you could run out of oil and suffer internal damage.

Check the level of your gearbox oil. Consider changing it. I would check that seal next. If you're going to check it you might as well replace it as the seal usually is not that expensive for a new seal.

  • I changed the oil 1 month ago. I am going to check the gearbox oil level tomorrow. Thanks for the tip! Commented Sep 12, 2017 at 21:11

If I recall correctly as it has been a long time since I have worked with 2 cycle engines. It requires mixing oil with the gasoline. If you have too much oil mixed with the fuel it will produce excessive smoking. I think depending on the manufacturer the ratio of gas/oil varies from 20:1 to 50:1.

  • The mix is made automatically by the oil pump and carb. I do not add the oil in the gasoline myself. Commented Sep 12, 2017 at 6:36
  • What color is the smoke? Is the engine air cooled or liquid cooled?
    – Old_Fossil
    Commented Sep 12, 2017 at 6:43
  • It is a water cooled engine. That is blue smoke, purely oil, no water. It does not lose any coolant. Commented Sep 12, 2017 at 6:44
  • Hmmmm....interesting
    – Old_Fossil
    Commented Sep 12, 2017 at 7:28

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