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Discussion Starter #1
Smoking and leaking carbs. I’ve had my 1971 CB350 restored by a guy in the uk. He delivered the bike to me after sometime but within 5 minutes the left carb started smoking with fuel spilling behind the carb somewhere. I will post the video to see if someone can give me any advice. It was s full restoration a enginecstrip down apparently but no proof to prove this.
He’s not interested in it anymore so putting it out here to the pro’s.
Originally posted in general discussion in the main forum but better posted in here thanks.

https://youtu.be/64P6z_ySrrc
 

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I would not start it again if you don't want it to catch on fire! Does fuel leak out when the petcock is on?
 

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The POD Air Filters you have on your bike are junk.
I hate to be so blunt but these bikes really don't like pod filters.
Are they better than nothing well not sure as they typically degrade the bikes performnce.
Most of the PODS on the market will block the vacum ports on the front of the carb intakes.

If you notice there is a Tube under your battery box, That is supposed to be a connection between the (2) OEM Airfilter Boxes.
The purpose of connecting them is to smooth out the pulses of the intake.

I suspect your smoking is pulses allowing atomized fuel to be pushed back out.
If the Carbs are actually leaking from the overflow that is usually a sign the Overflow Tube inside the float bowl is crakced a very common but easliy fixed problem.
It is a brass tube and the cracks are 99% very easy to solder closed.
 

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Discussion Starter #4
Sorry I had a better look at home when I got the bike back from my Mothers. I removed the pod air filter and found the crankcase breather tube right next to the pod. This is what starts smoking after 5 mins. The breather tube is slightly oily to touch as well. Eventually the bike just cuts out after 5 minutes. The fuel leak has gone which appeared around the back of the carb running down the frame. The fuel only leaked when the bike was on but at home appears to be fine now. The bike restorer said he took it out on a 20 mile ride which I do not believe. Is this normal smoking and something that will burn off? I only say that as the nike has not been on the running much in 30 odd years.
 

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Discussion Starter #5
Breather hose issue.

Heres whats going on. I catch the bike stalling within 3 mins and puffs of smoke and fuel/oil coming out of the breather hose

 

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Discussion Starter #6
As a total novice and guessing. Could the carbs be so incorrectly set up that they are flooding the engine and unburnt fuel is getting out of the breather hose, causing stalling through flooding or does the video suggest something more terminal. Ive checked the oil and the dip stick level is fine although I can't visible see the oil looking down and into the reservoir.
 

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Your engine has excessive blow by caused either by worn out parts like piston rings or valves or new parts not properly assembled an example being broken piston rings. You are also seeing water vapor.

A proper compression test will give you more answers.

In the meantime, are both exhaust pipes hot to the touch? That would indicate you have combustion happening.

These bikes don't like to idle for long periods and especially not on the side stand.

The hose should run down to the hollow in the frame an exit just below it in the area of the center stand.

The fuel leaking down onto the ground is from the overflow, something is/was holding the valve open that regulates the amount of fuel in the float bowl, could be a small amount of rust etc although the petcock filter should have caught it.

You are going to be on a steep learning curve.
 

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What's coming out of the breather tube, which by the way is waaay too short and not properly routed (it should go down to under the engine around the centerstand pivot area) seems to be a mix of either water and oil or fuel and oil, it's not typical for oil mist to be that thin. I'd have to say there's more blow-by crankcase pressure than there should be, which can often speak to the condition of the top end of the engine (primarily rings and pistons in this case)
 

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It was restored, does that mean fresh top end parts? New rings wont seat if you just idle the motor, get on it and ride it, it needs to get hot enough to expel the moisture.
 
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That is one noisy engine. That is way too much blow by. I think your rings are bad, and you have a vacuum leak at one or both carbs.
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