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CRF80 Smoking

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Hi All. New member here.... I just picked up a 2006 CRF80 for a great price. When I bought it I knew it was smoking. Now to figure out why. Hoping that members on this forum can help identify possible causes. I know the typical causes are valve seals and/or rings...the following info. might help...


Starts great. First kick - my assumption is that this means I have good compression

Runs well - doesn't feel like it bogs down

Smoke is white in colour

Smokes a little at idle

Smokes more as the engine works harder...


Is it possible to have good compression, easy starting but worn rings?


Next question...if it is worn rings what are the next recommended steps? Do I need to have the cylinder honed? Bored? If bored I know I need to replace the piston and rings. If honed/deglazed only do I need to replace piston or just a recommendation?


Thanks in advance

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First try dumping the oil and refilling with the proper weight oil. Clean air filter, replace plug. That will give you a good starting point. The only thing that makes these bikes smoke is lack of oil changes generally. If thats the case its top end rebuild time.

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Thanks ickfinger...


Will do. I will also try a compression test but from what I understand this is only half of the equation?? Do I need to do a leakdown test as well? or will the compression test tell me enough. I believe the compression should be approx. 170psi. At what psi rating is it time to rebuild...a 10% drop? 25?

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So I changed the oil. Didn't look good and only got 85% of what I should have drained. Started it up again and still smoking. So oil changed, spark plug changed, and air filter cleaned and reoiled. ....any suggestions....again starts first kick

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I read just moments ago someone had a similar issue. cause could possibly have been previous owner overfilled or used incorrect oil and pipe is holding old oil residue. Cleaned pipe with kerosene and took care of problem.... Also another suggested a hotter plug. I have the same issue with my xr100. Starts easily(1 kick) and seems to run really well.  I have not yet tried any of the remides(sp), but if I find out something I will post back here. please post back if you figure out something too ! thanks

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White smoke is typically a symptom of coolant

entering the combustion chamber. Since the

CRF80 is air cooled, THAT problem can be ruled


Blue/grey smoke is a symptom of excessive oil

where it should not be. Rings, valve seals and

valve guides are some possible causes.

Since the engine starts easily and runs well,

this suggests the rings (and valve/seats) are

sealing adequately.

If the intake valve seal or guide was bypassing

excessive oil, I would expect the resulting smoke

to be more blue than grey because the oil will be

drawn into the combustion chamber where it will

burn in the high heat of combustion.

I would expect smoke to be more prominent on

deceleration due to high vacuum on the intake

tract. Also, I would expect to see signs of oil

fouling of the spark plug.

If the exhaust valve seal or guide was bypassing

oil, I would expect the resulting smoke to be more

grey than blue because this oil enters downstream

beyond the combustion chamber and does not

experience the same heat. Because of reversion,

some oil may be drawn back into the combustion

chamber. However, spark fouling is expected to

be less evident than would be apparent for a similar

quantity of oil bypassing the intake valve seal/guide.

(I would not expect any appreciable change in smoke

as a result of changing oil in the sump, cleaning the

air filter, changing the spark plug, adjusting tire pressure

or polishing the spokes.)

A compression test gives a general indication of sealing

within the combustion chamber. If the test result is good,

most of us can stop here.

If the CT result is not so good or if someone has special

reason to want further diagnosis, then there is the option

of performing a Leak Down Test. The LDT requires additional

equipment, time, skill and care. In return, the LDT provides

insight into, proportionately, how much compression is being

lost and where.

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Eddy Curr did an excellent review of the test procedures and what to look for in each possible problem area.  My addition to this discussion is that when I bought my 1977 XR75 (and my 1982 Z50R for that matter) they also ran well and smoked at idle and when running.  The bottom line was that the engine needed to be bored for O/S piston and rings.  I also had the valve guides checked and new seals installed.  I would think that any more than a 20% reduction in compression would be cause for concern but I'm not an expert in this area.  Thankfully you have electronic ignition on this bike since you wont have to deal with the POS points ignition system like I did on mine.  Best of Luck!

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