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Author Topic: Carburetor fuel leak  (Read 277 times)
UnicornMaster
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« on: September 06, 2017, 03:36:01 PM »

Hey, everyone. 

New to the boards, but have lurked here for a while.  I went to start up my '89 CB-1 and smelled fuel, took a look around and it appeared to be leaking from the carbs. I'm green in terms of repairs, but don't have the cash to take it to my mechanic so figured now was the time to learn. Looking around, the most common likelihood was a stuck float/valve, so I got the carbs off the bike and opened up the bowls but all four floats move pretty freely, and the needle valves all look to be in good condition. 

Could one of them have been stuck and I happened to loosen them during this process? Is there a way to test the carbs while they're off the bike? Could it be the bowl gaskets/should I replace them regardless after opening the bowl? Something else that I should be looking at?

I appreciate any advice or resources you can point me to.  I have a copy of the service manual, but there's a certain amount of expected knowledge that I just don't have yet, being my first time trying to work on a bike.

Thanks,
Brian
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a_morti
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« Reply #1 on: September 06, 2017, 04:17:47 PM »

I can heartily recommend litetek seals.
http://litetek.co/Carb_Kit_Honda_CB1_NC27.html

Made of viton rubber they are more resistant to ethanol in modern fuel than original (30y old) parts.

Changing them isn't so hard, just be methodical. You do need to be careful with all the springs, plus you may need to pay the mechanic in the end for balancing them together. Also be careful with the original screws, you need a Philips number two and ideally, grind the tip a little flatter so it's more compatible with Japanese screw heads. Give it a sharp tap with a hammer before trying to remove each screw.

Not too tricky. I've done a few.
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UnicornMaster
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« Reply #2 on: September 06, 2017, 06:40:05 PM »

Thanks!  I came across this kit earlier today, good to hear they're a solid buy.

On another note, I just learned that if my float needles have a ring on them, they need replacing.  I called my local Honda shop and the part has been discontinued.  It's quite possible this is the cause of the leak, not fully closing the fuel supply to the bowl.  Anyone know if there's a 3rd party source for this sort of thing? Or a generic part that does the trick?

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jdg25
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« Reply #3 on: September 06, 2017, 07:18:55 PM »


On another note, I just learned that if my float needles have a ring on them, they need replacing.  I called my local Honda shop and the part has been discontinued.  It's quite possible this is the cause of the leak, not fully closing the fuel supply to the bowl.  Anyone know if there's a 3rd party source for this sort of thing? Or a generic part that does the trick?


Had this bookmarked:
http://www.hondacb1.org/forum/index.php/topic,2494.0.html

TLDR; 87-88 600's had the same carbs. Links to float needle reference chart and item page below.

Ref chart:
https://www.jetsrus.com/needle_valve_float_bowl_gasket/needle_valve_by_manufacturer.html

Aftermarket/Genuine part links:
https://www.jetsrus.com/individual_parts/KL_18_8953.html
https://www.jetsrus.com/individual_parts/018_880_su.html

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UnicornMaster
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« Reply #4 on: September 06, 2017, 07:25:53 PM »

Awesome, thanks! Will let you know if I find them  Grin
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a_morti
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« Reply #5 on: September 06, 2017, 07:28:50 PM »

I think more likely it's a float bowl o ring, or even more likely it's one of the seals on the fuel rail T joint. Those get flat/hard, then tear just slightly when the T is moved. Wouldn't hurt to change all relevant seals, but I'd start with the Thai kit as it's more likely to solve the problem.

Ideally though, you should diagnose the problem before getting stuck in.
« Last Edit: September 06, 2017, 07:32:55 PM by a_morti » Logged

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Pod70
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« Reply #6 on: September 07, 2017, 08:37:34 AM »

It's quite common for the floats to stick open if the bike has been sitting unused for a while and all that is needed is a sharp tap to the float bowls to release them.
You can check the needle valves by turning the assembled carbs (minus the float bowls) upside down and blowing through the fuel pipe. If one isn't seating properly then you will hear the air leaking past it - or give yourself a hernia if they are all fine  Grin
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Efreeman55
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« Reply #7 on: September 07, 2017, 12:40:22 PM »

A while back I discovered a big fuel leak when I started my CB-1.  Pulled the carbs and discovered the O-rings on the tubes were leaking.  Used the Litetek kit to replace all the seals and fixed the leak.  Take plenty of pics before you disassemble the rack of carbs so you get everything back together properly.  If you can't, I can send you the pics I took of mine.  It's a bit fiddly and tedious but easy to do if you're mechanically inclined.

Eric
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