Author Topic: Another carb overflow - scary experience  (Read 691 times)

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Offline Erny

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Another carb overflow - scary experience
« on: May 30, 2020, 02:57:57 PM »
Let me share what happened to me today with my CB550K1
 
we were riding half day, on the way back, after ~120 miles,  there was wet road after rain (we started to have soaked pants etc) , suddenly I felt engine irregular run, so turned petcock from main to reserve (normal after rinding 116miles from full tank), after few second engine started to run  OK again.
By that time we entered into small city zone and after another few mins of drive I started to felt rear tire slipping (I was going straight, speed around 30mph). First tought was what the hell? Oil on the wet road? Then I tried to carefully apply rear brake, real wheel went to block immidiately and was slipping like on the ice. F*!!, I got flat tire, I thought. Even stronger acceleration turned wheel to slip! I stopped, looked at tire, but it looked OK!. Not far from that place was petrol station, so I carefully continued there and when I stopped and started to examine bike in detail, I found HUGE petrol leak from overflow hoses...
It was from carb #2. I immidiately understood what happened - fuel leaking right in front ot rotating rear tire, combined with water from the road...like lubricating tire!. If this would happen suddenly in some turn I cannot imagine how can I keep bike on the road!!!

BTW, I did not manage to fix that leak by knocking on carb there, so I continued ride with petcock closed and opening just for few seconds to fill bowls and close again and repeat in cycle till I arrive home to prevent leak. When home, I tried again to knock on the carb/bowl with wooden stick but still the same, so I need to open that carb  :(
More I'm thinking about I suspect it is linked to moment when I changed main to reserve fuel, maybe some bigger piece of debris from reserve passage that blocked carb #2 valve???

Did anybody ever had similar issue?
Now I thnk that design with overflow hoses ending right in front or rear tire is really DANGEROUS as it seems can happen anytime  :o

Sorry for bothering you with this... maybe I should use another forum?
« Last Edit: May 30, 2020, 02:59:34 PM by Erny »
CB750K K7 USA model (1977)
CB550K1 USA model (1975)

Offline scottly

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Re: Another carb overflow - scary experience
« Reply #1 on: May 30, 2020, 03:51:19 PM »

Now I thnk that design with overflow hoses ending right in front or rear tire is really DANGEROUS as it seems can happen anytime  :o

I agree that the hoses should not be right in front of the tire!!! Likewise for the vent hoses from the oil tank and valve cover on the 750s.
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline ekpent

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Re: Another carb overflow - scary experience
« Reply #2 on: May 30, 2020, 04:30:56 PM »
Probably when the float bowl was going dry before you switched to reserve it lowered the float to an extreme and then your float needle got jammed when fuel came back in from switching to reserve causing it to overflow since the float was also jammed up.Does sound like a scary experience, glad your OK.

Online PeWe

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Re: Another carb overflow - scary experience
« Reply #3 on: May 30, 2020, 11:20:36 PM »
Similar happened to me in the early 80's.
Fuel hose came loose and sprayed rear tire with fuel. K6 tank, one hose.
Just after a long straight road when enter a very sharp curve, very short of time to react.

I had my girlfriend on bike too so I cruised not that fast as usual. I could not turn enough in the corner, happy for us no meeting traffic.
My normal speed might have ended up in a bunch of trees.

About the overflow tubes, I have always seen the assembly right in front of tire as an idiotic design. A safety hazard that should have been reported via a Service bulletine with a fix, almost 50 years ago.

Battery hose leaking on chain got a bulletine.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Erny

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Re: Another carb overflow - scary experience
« Reply #4 on: May 31, 2020, 08:21:22 AM »
I'll try to find another route for hoses to the side.
I'll need longer (new) hoses - what's correct size I should buy?

CB750K K7 USA model (1977)
CB550K1 USA model (1975)