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Vent Pipe Smoking

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Garryk:
Was wonder if someone can help me with the following issue.
There is what looks like a vent pipe coming from the top of the engine then runs over the top of my airfilter and then runs down the back of my airfilter,ive noticed smoke coming from the pipe at the open end behind airfilter,bike seems to be running fine and no smoke from exhaust,im just hoping it something simple.
1975 CB750K5
Garryk

hairygit:
Is it smoke or steam/water vapour? If the bike is used infrequently or for short journeys condensation forms inside the engine, and can give the inside of the oil filler plug/dipstick a coating of greyish gunge, then if ridden for a while and the engine gets properly warmed up, the condensation boils off, giving steam through the breather which is often mistaken for smoke. Take a look at the dipstick, it can tell you a lot! Also, a little bit of blowby on the rings and general pressure build up in the crankcases is not uncommon on older bikes, the Honda manual actually mentions checking the end of the vent pipe to clear any oil or muck which may have accumulated there, so probably nothing to worry about unless it is smoking like a 2 stroke!

Garryk:
Hairygit many thanks for your help.
I only bought this bike 8 weeks ago,previous owner had her for 4 years and never really took the bike out as he was getting probs keep her running on 4 cylinders,i sorted that out with help from others on this forum,it was the dirty carbs causing the problem at the time,the bike has nearly 14,000 miles on the clock,unsure if they are genuine miles or not but she is in perfect order and most bolts and screws seem untouched,i noticed the smoke/steam coming from the pipe a few times and it always seemed on short journeys of 7 to 8 miles,longest distance ive had the bike so far was 80 miles and never noticed any smoke/steam,i havnt been using the bike much due to the weather,so im hoping what you said above about the steam is what the problem is,or should I say praying that's what the problem is,i will keep an eye on the issue and see if it vanishes with the better weather on it way.
Cant thank you enough for your help
Respects
Garryk

K2-K6:
Good advice from Hairygit there and if used more regularly then it should improve if that's the case.

The pipe is, as you've already mentioned a breather pipe......this is because engines can pressurise themselves during normal running, so to prevent that happening and trying to force oil out via seals etc then having a vent pipe allows the internal pressure to vent to atmosphere.

As hairy says, if there is water contained in the oil (it gets into the oil from short runs and or too much running on choke) as the engine heats up, then it can be seen as steam from the pipe.

In addition to hairy's advice of looking at the dipstick, just smell it as well.....it should be just oil (I know that sounds obvious) and not of petrol. If there is a noticeable petrol smell then it needs changeing.

More use should definitely improve it, and if the weather stays like today then you may get more chance to ride it as well.

Garryk:
Hi K2-k6
Many thanks for your reply and help,will check dipstick tomorrow for petrol smell,gave the dipstick a visual check  the other day and no signs on it of anything other than oil...
Im hoping to change the oil in next few weeks.
Here's to better weather.
Garryk

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