Author Topic: Can't get fuel to float chambers  (Read 276 times)

Offline Charliecharlcomb

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Can't get fuel to float chambers
« on: March 18, 2021, 04:46:10 PM »
(Problem also posted onto group on Facebook - the only reason I still use it)

I've been fettling my 1976 CB500 K2 - New Dyna S electronic ignition, new battery, reset float levels, that sort of thing. The carbs were NOS around 8,000 miles ago but as the bike hasn't been used nearly enough, it has stood dry for a few years. Last year I gave them a thorough clean, changed the O rings etc. and brought the bike back to something approaching a smooth runner again after the usual battery charging problems.

This time around having fitted the Dyna S and reset the float levels (they were out by quite a lot) I thought I'd check that fuel was getting to the float chambers by removing the drain screws. Only a couple of drops of fuel on each one, I was expecting it to be flowing freely. Moving up the chain, the petcock and fuel lines are new, the tank filter is clean, fuel runs freely from the tap and the tank breather is OK too.

Blowing down the fuel lines to the carbs it seems completely blocked. Once I've split the carbs and I blow down a pipe attached to the T fuel connector (blocking the line that connects to the tank) it feels blocked too on each carb.

I've checked everything else in the carbs as best I can and they seem clear.

So my question is - If I blow down the fuel line, should it feel blocked or is there a way of clearing the fuelway from the T connector into the carb? As this is the same for all the carbs I can't believe it's a simple blockage, I must be doing something wrong.

I'm looking to get fuel flowing freely to the bowls so it comes easily out of the drain plugs again.

Has anyone experienced this before and can they help?

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Offline Bryanj

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Re: Can't get fuel to float chambers
« Reply #1 on: March 18, 2021, 05:51:21 PM »
Sounds like you have the float level wrong and/or the needle valves are sticking.
There are spring loaded pins in the end of the needle valve which need to be free and the tang on the float has to only just touch the pin when floats at correct height.
The givaway is you say it ran but when you checked the floats were out by a lot

Offline Johnwebley

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Re: Can't get fuel to float chambers
« Reply #2 on: March 18, 2021, 05:51:40 PM »
The needle valves may have gummed up.

You could try filling with a solvent like acetone, or Redex cleanser.

Otherwise it's carbs off and dismantle, and clean.

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Offline Charliecharlcomb

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Re: Can't get fuel to float chambers
« Reply #3 on: March 18, 2021, 06:44:08 PM »
Sounds like you have the float level wrong and/or the needle valves are sticking.
There are spring loaded pins in the end of the needle valve which need to be free and the tang on the float has to only just touch the pin when floats at correct height.
The givaway is you say it ran but when you checked the floats were out by a lot

I've got the carbs off and have removed the outer two carbs as per the photos, if I take off the float bowl and spring loaded pin, should I be able to blow through the fuel line as it enters the carb? I'm looking for a way of knowing there is no further blockage before bolting it all back together again.

Offline Johnwebley

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Re: Can't get fuel to float chambers
« Reply #4 on: March 18, 2021, 06:48:27 PM »
Yes.

But do it with the float bowl off.

And make sure the float drops away from the needle.

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Offline Charliecharlcomb

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Re: Can't get fuel to float chambers
« Reply #5 on: March 18, 2021, 06:53:21 PM »
Yes.

But do it with the float bowl off.

And make sure the float drops away from the needle.

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I'll give that a go tomorrow and report back, thank you.

Offline Charliecharlcomb

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Re: Can't get fuel to float chambers
« Reply #6 on: March 21, 2021, 02:11:22 PM »
Sounds like you have the float level wrong and/or the needle valves are sticking.
There are spring loaded pins in the end of the needle valve which need to be free and the tang on the float has to only just touch the pin when floats at correct height.
The givaway is you say it ran but when you checked the floats were out by a lot
Almost certain this is the problem now. I'm in the middle of a complete carb stripdown and nothing is blocked, the insides are in really good condiiton so I guess I set the float levels too low with the end of the needle valve slightly compressed. Thanks for the great advice.

Offline Charliecharlcomb

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Re: Can't get fuel to float chambers
« Reply #7 on: March 23, 2021, 12:16:00 PM »
Set the float heights correctly this time, started her up and she purrs. Beautiful.

 

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