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Fuel above carb diaphram

  • Thread starter Thread starter loud et
  • Start date Start date
L

loud et

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So as I have gotten pretty good with the BS series Mikuni carbs, I have helped a friend or two rebuild a set for their 4 cylinder GS's. All went well as expected each time and I didnt come across and problems I hadnt seen before on a set of my own.
Now I am doing a set of carbs for my friends 82 Yamaha xs650 twin.

Its the same basic BS 32 carb body with some minute differences. The rebuild procedure is the same.

The only issue I have found upon disassembly is that when I removed the carb top cap (diaphram cover) , it was wet with what smelled like gas. I am not ruling out that it was some form of spray someone used but it seemed like gas that had gotten in there. There was also a little bit of pooling down where the needle clip is down in the center. Both carbs has the same thing going on.

Two things I found wrong with the carbs upon disassembly were 1- there were no orings on the threaded end of the choke plunger assembly. The choke plunger is plumbed right into the upper diaphram cavity, but below the diaphram so I am not sure if fuel could get in there.
The other thing I found odd was that the fuel needles looked excessively sharp and tapered as if someone had sanded them down.

Could either of those 2 things ( tapered needles or lack of o ring on the fuel plunger threads) cause this fuel getting ABOVE the diaphram?

If not...... any guesses?
 
When I did mine, I also found fuel above the diaphragms. Mainly just enough to moisten the space and collect a bit of dust.
If i recall, both Blowerbike and Rapid Ray said its not unusual.
 
Don't know because when I rebuild a set of carbs they haven't run in years. But if you think about it yes you would have some fuel up there. The slide operates off of vacuum generated, by the flow of air, in the throat of the carb. So what it is actually sucking is the air/fuel mixture present in the carb throat.

Just my opinion and hopefully some more knowledgeable than I will chime in.
 
Well I am giving the carbs a proper rebuild as always so I will just go with it.....
I never came across fuel moisture there before....makes me think that most of the carbs I have done (6 sets) were all on non running bikes or bikes that had only been shortly test ridden.
Cross my fingers I guess that it's a normal condition.
 
I suppose you could get some fuel in there when snapping the throttle closed. But I'm not an expert in the matter so I won't embarrass myself by trying to explain further.

Tapered needles could simply be aftermarket needles. My 750E came with a DJ3 kit in it, even though the airbox and exhaust were stock (!). Ended up doing a swap for stock ones (along with the proper jets) with a fellow member and it ran way better.

Or that could simply be the right taper for an XS650.
 
eil said:
I suppose you could get some fuel in there when snapping the throttle closed. But I'm not an expert in the matter so I won't embarrass myself by trying to explain further.

Tapered needles could simply be aftermarket needles. My 750E came with a DJ3 kit in it, even though the airbox and exhaust were stock (!). Ended up doing a swap for stock ones (along with the proper jets) with a fellow member and it ran way better.

Or that could simply be the right taper for an XS650.
Click to expand...

Yeah Eli, I'm no yamaha expert.....I checked all the jets in the carbs vs the web and they are all stock. The needles most likely are too.....just quite a different taper thank our rather blunt GS needles.
I finished the carbs last night and bench synced them so they are ready to install.
Case closed for now. Lol.
 
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