Smoking At Idle: Yamaha Fresh Small Bike

[ClareQuilty]

The other day I bought a Yamaha Fresh motorbike, I guess with the usuall four-stroke 100 or 110 cc Yamaha engine. I have another Fresh which has been fairly reliable, so I bought this one from the same dealer without paying enough attention, and now I see that it smokes intermittently.

It may be smoking a little at all times, but only smokes profusely at LOW idle - real mosquito-fogger effect. The bike doesn't seem drastically different in power from the non-smoking one I have, so I guess it still has some fair degree of compression.

Can anyone guess if this is the ring(s) or the valve? And can anyone advise how long the engine might continue to run with this problem? I hesitate to go for a re-build as the bike's not worth it - a four-stroke rebulid is quite expensive (something like 1,800 baht).

[Plucky]

You've clearly had your ring stretched.

[ClareQuilty]

You've clearly had your ring stretched.

Haha, yeah I guess the ring is worn out. But why does it smoke more at idle than normal operation? And how much longer might I reasonably expect it to last?

[transam]

First do a couple of tank fulls of gas in case there has been oil inadvertently contaminate the fuel. After that, if a real smog then it looks like rings or perhaps valve seals, but only a strip down will reveal all.

[Garry]

Use a leak down tester first before stripping an engine.

Sent from my iPhone 3 using ThaiVisa app

[ClareQuilty]

Guys, thanks, but I'm not going to 'strip it down' (or rather, have it stripped down). I don't want to spend much money on it. I was just wondering if the nature of the smoke (lots at low idle, but only a little during normal driving or even when the idle was set quite high) could give a clue as to whether it was the rings or the valve-guides, and also whether anyone could hazard a guess as to how long a small bike engine might run this way.

One guess I had as to why I didn't notice the smoke when I bought it (besides the high idle), was maybe the oil in it was so old and thick (and possibly low), that it didn't smoke as much. I really noticed the smoking after I had the oil changed. Might it be advisable to change it again and put in the thickest oil available?

[transam]

Drain the crank case and fill with the recommended oil . Do a couple of tank fulls of gas and see what happens.

[wantan]

These Yamaha Fresh are strong bikes. Maybe the bike will run for another 50,000km while smoking. But does this really makes you happy? Riding a smoking bike to save the costs for a repair?

I hope transam is right and it will get better with just a bit fresh oil and gas. But i would take the recommended oil. Thicker oil won't help much i guess. You only risk a complete breakdown.

[Lickey]

CQ, check the crankcase breather, not sure where it is on a Fresh, it might be a rubber pipe going into the airbox/filter housing, if this is partially blocked it will increase case pressure at lower revs and clear at higher revs, if it blocked it will cause piston and valve blowby,

Another thing you could try is start engine, remove oil filler cap, put your thumb over hole and test for pressure, none means its breathing ok, pressure means that the crankcase breather is blocked,,

[ClareQuilty]

Maybe the bike will run for another 50,000km while smoking. But does this really makes you happy? Riding a smoking bike to save the costs for a repair?

Yeah, not happy exactly but being a teacher in Thailand means, well, lets just say the meaning of a baht changes... and it gets worse the longer you stay!

CQ, check the crankcase breather... start engine, remove oil filler cap, put your thumb over hole and test for pressure, none means its breathing ok, pressure means that the crankcase breather is blocked

Thanks Lickey, I'll try this. Will oil shoot out on me?

[BirdsandBooze]

Have a look at your spark plug - if it's sooty your fuel mixture is too rich. If the plug is oily then oil is what you're burning. What colour is the smoke? If it's blue you're burning engine oil. You say the oil has been changed, in which case check the oil level to make sure it hasn't been overfilled. These bikes only have a small oil capacity so putting in too much oil is easily done and will lead to burning and overheating. If the oil level is okay the culprit will likely be rings/valve seals/worn bore/breather - a couple of hours work for you to renew/clear or for back soi 'mechanic' Somchai to make matters worse. Grey black smoke is caused by a worn pilot jet/too rich fuel mixture, so replacement/adjustment should cure that.

[roban]

How old?

How many Km's?

Last oil change?

More details please.

how long the engine might continue to run with this problem?

A look into the crystal ball says: something between 100-100000KM.

But seriously, its an old bike, and of course with a lot of KM, so you can expect, that everything is more or less worn out.

Piston rings and valve seals are the "usual suspects" in your case.

But any further speculation is useless, if you can't/won't afford the 1800 Baht for a repair....

[VocalNeal]

My knowledge of Yamaha is zero. But as has been said the culprit could be the crankcase breather. On a Honda there is no tube breather. The breather is built into the crankcase so it maybe the same on a Yamaha. If it is not look around the engine for a small rubber hose that points downwards. The plastic one will be the drain from the battery area, and the other small one will be the carburetor overflow pipe. the one you want is about 3/8" diameter and if it exists will be at the back of the engine.

Again as has been said unscrew the oil filler and see if the smoke disappears. If it does your mechanic may know where the breather outlet is and be able to unclog it.

Remedy? Older engines are not designed to use modern oils so get the oil changed and use 20W/50 it is thicker and will not "leak" . It is not easy to find but worth a look.

Finally. Claire why not pretend it is one of your beloved two-strokes

[ClareQuilty]

Been driving the bike now for a week or two, and I think 'what the heck' - it runs and drives. There's no need to worry about a little smoke (though it can really smoke people out behind me at the stoplights as we wait - always good for a laugh when the farang has the worst bike or car in the traffic).

[BSJ]

Been driving the bike now for a week or two, and I think 'what the heck' - it runs and drives. There's no need to worry about a little smoke (though it can really smoke people out behind me at the stoplights as we wait - always good for a laugh when the farang has the worst bike or car in the traffic).

Ahh, same attitude as the Thai's. Don't you ever wonder about the effect of all the exhaust fumes are doing to other people....and yourself?