small amounts of smoke at startup?

4 replies to this topic
  • rubenz

Posted June 18, 2004 - 01:56 AM


so i just recently traded my dr350 for a 650L. it runs aboslutely great but at startup there is a tiny bit of smoke that burns up and is gone really quickly. shouldi worry about it? just use it as is? what would i replace or check? any other suggestions. :thumbsup:

  • yooper_porkchop

Posted June 18, 2004 - 02:06 AM


Use it, just keep an eye on the oil level, if it uses oil excessivly you my have to freshen it up.

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  • qadsan

Posted June 18, 2004 - 05:16 AM


What color is the smoke? White is usually from water. Black is usually from too rich of mixture, but some puffing of black smoke on startup can also be an oil control issue. Blue or blue/white is usually from oil. Your oil level will also help to clue you in to an oil control issue.

If you're getting a puff of black or blue tinted smoke on start up only, the problem may likely be related mostly to the valve guide seals. If you're twisting your throttle when the bike is warming up and the puff of smoke is more prevalent right after you let off the throttle, then I'd venture to say that it's likely the intake side that's mostly contributing to this. When the engine is cold and tight and when you're reving your throttle, manifold vacuum may be drawing oil down the valve stem and into the combustion chamber where it's partially burned, which in turn produces a puff of black or blue smoke. Once the engine gets warm, the oil is burned off and you may not see the smoke anymore (depending on how much oil there is).

Don't forget to check the obvious things such as putting too much oil in your bike, an over oiled air filter, etc, but a puff on start up only is more likely related to the valve guide seals than the rings, too much oil, etc.

Unless your oil level is drastically changing after every ride, your engine may run a very long time like this and shouldn't cause any harm except for fouling spark plugs a little more often (depending on how bad things get).

  • heliosstudios

Posted June 18, 2004 - 07:33 AM


There is a way to tell if it is the rings or guides. Using a compression tester, measure the compression cold. Then pour a tablespoon of clean motor oil into the sparkplug hole and test again. If there is little or no discernable change in compression, then the rings are fine.

I wonder if the engine design has anything to do with this smoke problem since a lot of people seem to experience it. Perhaps it is due to oil that leaks past the valve guides, but does so because of the quantity of oil left sitting above the valves?

  • JR650

Posted June 18, 2004 - 09:00 AM


heres a theory for you. Lots of the air cooled Xr's seem to do this. I wonder if the factory doesnt use alot looser tolerances in the engine (piston to wall, ring gap, etc) to compensate for things expanding when they get hot. Air bikes run alot hotter than liquid ones. just a thought, JR

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