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Author Topic: Carb leaking a small amount of gas at rubber intake boot (picture)  (Read 1259 times)

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Offline gregripko

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Carb leaking a small amount of gas at rubber intake boot (picture)
« on: October 17, 2013, 10:31:35 AM »
Noticed overnight a little saturation of gas at the rubber collar (rubber piece that connects carbs to engine) of the outside carb... How can fuel be in here after fuel has been turned off and engine isn't running? Any solutions?
« Last Edit: October 22, 2013, 04:34:22 PM by gregripko »
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Offline PeWe

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Re: Carb leaking a small amount at rubber collar
« Reply #1 on: October 17, 2013, 10:49:58 AM »
Dripping from the petcock?
If it is the old type that CB750 had, attached with 2 screws in the tank. o-ring here tired, screws not tightened enough. The 2 screws must have a fiber washer under the head.
Carb bowl Ok, mine had a hole which other have had here too.

Thread: http://forums.sohc4.net/index.php?topic=111676.msg1451901#msg1451901
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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 TwoTired

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Re: Carb leaking a small amount at rubber collar
« Reply #2 on: October 17, 2013, 11:31:08 AM »
The carbs get fuel by gravity.  Fuel valves can leak.  Check the oil for gasoline contamination.

Outside carb is #1 or #4?
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline gregripko

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Re: Carb leaking a small amount at rubber collar
« Reply #3 on: October 17, 2013, 12:20:51 PM »
Outside carb #1 between the carb intake boot and the metal piece that holds carbs together....
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Offline TwoTired

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Re: Carb leaking a small amount at rubber intake boot
« Reply #4 on: October 17, 2013, 03:09:23 PM »
# 1 is the lowest carb when on the side stand.  As liquids are self leveling due to the earth's gravity, a leaky float valve can allow the bowl to overflow with fuel remaining in the fuel supply lines.

Best hope that is what it is. a leaking fuel tank valve would leaky until there isn't fuel in the tank, draining into the intake runner, the cylinder and into the oil pan.

Check your oil supply.  You might also lessen the lean over with a side stand spacer block.  Or use the main stand.

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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline gregripko

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Re: Carb leaking a small amount at rubber intake boot
« Reply #5 on: October 17, 2013, 04:21:58 PM »
I felt like the lean on the side stand might come into play and I also have a slightly long fuel line on carb 1 & 2 (cb550) that I need to cut back... I'll look at it and make the free/cheap fixes before diving into any large endeavors
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Offline gregripko

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Re: Carb leaking a small amount at rubber intake boot
« Reply #6 on: October 17, 2013, 04:29:39 PM »
If it was the float valve wouldn't it be coming out of the overflow and not the boot?
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Offline ANDY W

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Re: Carb leaking a small amount at rubber intake boot
« Reply #7 on: October 18, 2013, 07:25:24 AM »
sounds like the petcock of the supply line is leaking a small amount. if the float valve was leaking i think u would more likely see it drippint out of the overflow tube not a sealed connection bettween the carb and boot. easy way to find out is stick a piece of news paper under the petcock and under the over flow tubes
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Offline gregripko

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Re: Carb leaking a small amount at rubber intake boot
« Reply #8 on: October 18, 2013, 08:12:36 AM »
I'll check both when I get the chance.... My fuel line for carbs 1 and 2 is also pretty long... I was initially guessing that when I turn the petcock off there was still a decent amount of fuel in the line that has nowhere to go except through maybe a small crevice.
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Offline PeWe

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Re: Carb leaking a small amount at rubber intake boot
« Reply #9 on: October 18, 2013, 11:18:33 AM »
Important to verify overflow in carb caused by float valve not closed as TwoTired wrote.
This can enter the engine and mix with the oil.  I've read another thread about it earlier today. Really bad for the engine!
I got overflow in one carb last week, carb 1 of course!  Gas squirting thru the airjet.  Bike standing on side stand might helped the problem to arise..
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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 gregripko

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Re: Carb leaking a small amount at rubber intake boot
« Reply #10 on: October 18, 2013, 11:43:51 AM »
Gas wasn't present went I looked this morning.... Next off day I have I'll replace float valve while I'm in there just to eliminate possibility
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Offline gregripko

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Re: Carb leaking a small amount at rubber intake boot
« Reply #11 on: October 21, 2013, 03:07:37 PM »
Ok I changed the float valve and verified that it is not leaking when the floats raise... My concern is that gas might be getting into the engine... Is there a solution to this or steps to solve this issue? Trying to think of other potential issues...
« Last Edit: October 21, 2013, 03:26:41 PM by gregripko »
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Offline gregripko

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Re: Carb leaking a small amount of gas at rubber intake boot (picture)
« Reply #12 on: October 22, 2013, 04:34:56 PM »
Posted a picture in my original post above of my issue... Appears to be coming from the boot and draining downward towards carb bowl
« Last Edit: October 22, 2013, 04:40:38 PM by gregripko »
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