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New bike, new problems. Carbs leaking. Float valve?

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calyx
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Joined: 11 Dec 2008
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PostPosted: 09:15 - 26 Jul 2011    Post subject: New bike, new problems. Carbs leaking. Float valve? Reply with quote
I bought a 1980 honda cb400 two days ago and the problems started straightaway Laughing
Carb overflow tube is leaking. But it is not too bad. 3 drops in 2 minutes-ish. Gets worse with the speed.
Am I right thinking it is the float valve causing the fuel leak?
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MarJay
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Joined: 15 Sep 2003
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PostPosted: 09:18 - 26 Jul 2011    Post subject: Re: New bike, new problems. Carbs leaking. Float valve? Reply with quote
calyx wrote:
I bought a 1980 honda cb400 two days ago and the problems started straightaway Laughing
Carb overflow tube is leaking. But it is not too bad. 3 drops in 2 minutes-ish. Gets worse with the speed.
Am I right thinking it is the float valve causing the fuel leak?


The float valve stops too much fuel from entering the carburettor by having a needle and float that floats in the floatbowl. The needles sits on top and seals off the inlet to the carb when the floatbowl is full.

These needles are made of brass (as are the needle seats) and can wear a little ridge in the tip. I found this to be the case on my 350LC. But I also found a small fragment of leaf had somehow made its way into the needle seat. I replaced both the seat and the needle and removed the leaf and everything was fine afterwards.
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Bezzer
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PostPosted: 09:21 - 26 Jul 2011    Post subject: Reply with quote
Probably the valve seat/seal, may be either worn or a bit of crud stuck in it preventing it sealing properly. Won't be the float itself as there would be a lot more petrol pissing out if it was. Could try tapping the carb body to see if that shakes anything loose from the seal but you're best off stripping, cleaning and checking the carbs. Spares are easy enough to get from NRP, Allens Performance etc.

edit...too slow, wot Marjay says Mr. Green
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calyx
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Joined: 11 Dec 2008
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PostPosted: 09:37 - 26 Jul 2011    Post subject: Reply with quote
The one on the right is needle seat right?

https://img560.imageshack.us/img560/703/needle.jpg
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MarJay
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PostPosted: 09:56 - 26 Jul 2011    Post subject: Reply with quote
calyx wrote:
The one on the right is needle seat right?

https://img560.imageshack.us/img560/703/needle.jpg


Erm... the ones on my 350s were a LOT smaller than that. But maybe yeah.
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calyx
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PostPosted: 10:12 - 26 Jul 2011    Post subject: Reply with quote
It's just a random photo I found on the net Very Happy

Luckily I can remove the float bowl without removing the carbs. Now I am running late for my car test. I'll check the carbs later. Wish me luck Laughing
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MarJay
But it's British!



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PostPosted: 10:20 - 26 Jul 2011    Post subject: Reply with quote
You want to buy something like this:

https://www.jerryscycles.com/catalog/i366.html

The silver thing in the top left looks like the needle seat although on most bikes I've looked at it is brass.

Hmm... Maybe you want...

This: https://www.wemoto.com/bikes/Honda/CB_400_NA_Super_Dream/78-80/picture/Carburettor_Gasket_and_Float_Valve_Kit/
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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calyx
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PostPosted: 11:53 - 27 Jul 2011    Post subject: Reply with quote
Tapping the carb body solved the problem Shocked
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Carvel
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Joined: 01 Jun 2010
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PostPosted: 12:03 - 27 Jul 2011    Post subject: Reply with quote
Twas probably a sticky float

My superdream was pissing petrol out of the overflow for the right hand carb, took the bowl off and moved the float up and down a few times and it stopped.
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