76 Yamaha 650 spilling fuel?

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HotRdd - 02 Apr 2007 19:25 GMT

I finally thought it might be time to pull the old Yamaha 650 out of the
garage and see if I can get it ready for summer. I had the motor re-built a
couple of years ago and then never finished the project. I pulled the bike
out, charged the battery and fired the thing right up, no big problems
except with the petcocks open the fuel is spilling out of the carbs/hoses.
What's the deal? What can I do to stop the carbs from dumping fuel all over
the floor when the petcocks are open?

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someone@some.domain - 03 Apr 2007 04:34 GMT

>I finally thought it might be time to pull the old Yamaha 650 out of the
>garage and see if I can get it ready for summer. I had the motor re-built a
[quoted text clipped - 3 lines]
>What's the deal? What can I do to stop the carbs from dumping fuel all over
>the floor when the petcocks are open?

stick something under to collect the fuel and see if the
gaskets re-seal. they can dry and shrink. sometimes they
will swell and be normal again. if not, it's rebuild time.
i would actually suggest better percocks. the stockers are
crap, unless you're doing a cosmetic resto too.
you can get very simple 2 position petcocks cheap. use a
tube inside one for running and use the stock for reserve,
like the brits did.

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E M F - 03 Apr 2007 05:31 GMT

Hot Rdd scribbled;

>I finally thought it might be time to pull the old Yamaha 650 out of the
>garage and see if I can get it ready for summer. I had the motor re-built a
[quoted text clipped - 5 lines]
>
> Sounds like your float valves are stuck wide open......GC

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HotRdd - 03 Apr 2007 14:46 GMT

Any idea where I can find information on checking the carbs and setting the
timing on the bike etc. or is it time to take it to my mechanic?

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ShadowHawk - 04 Apr 2007 21:21 GMT

Chances are that there's at least 2 problems that need to be addressed:

(a) Petcock (is yours vacuum actuated?) leaking. This means a repalcement
diaphragm kit for teh petcock. Easy to do on your own (or you can get a
new petcock wth on/off/reserve positions)

(b) Carb floats(s) in teh bowls are not rising when there's fuel in there
to shut off teh flow when the bowl is full.

Hitachi or Mikuni carbs? Never mind - really doesn't matter (though -
if you have overflow hoses - it's probably Mikuni's)... Either way - you
can check/fix - maybe while still mounted on the bike... perhaps will need
to pull them - but the floats may be stuck.. or maybe a piece of debris in
the closing/fill mechanism letting it leak...

Another thing to watch for now, is for fuel in the crankcase. If the carbs
overflowed, and one fo teh cylinters happened to be sitting with an intake
valve open, then you've most likely got gasoline in the crankcase oil.
Open the oil-fill cap, and smell the crankcase. Iffin' it smells like
gasoline - I'd definitely change the oil & oil filter once you have the
problem(s) fixed. Gas in the oil will take away the lubricating properties
of the oil, and *can* lock up an engine.

Easy enough stuff for most bike owners who like to tinker... or most any
shade-tree mechanic. I've done this work on several bikes, and wouldn't
hesitate to do it again.

G'Luck!
Rex S.
'82 XJ650 Maxim
'82 XJ750 Seca (Project)

> I finally thought it might be time to pull the old Yamaha 650 out of
> the garage and see if I can get it ready for summer. I had the motor
[quoted text clipped - 3 lines]
> of the carbs/hoses. What's the deal? What can I do to stop the carbs
> from dumping fuel all over the floor when the petcocks are open?

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HotRdd - 09 Apr 2007 15:20 GMT

It looks like the carbs. have sealed themselves again after letting the fuel
sit for a while. Now the starter seems to be jammed. Any ideas whatrwould
cause the starter to jam?

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flynrider - 11 Apr 2007 01:44 GMT

>It looks like the carbs. have sealed themselves again after letting the fuel
>sit for a while. Now the starter seems to be jammed. Any ideas whatrwould
>cause the starter to jam?

If you indavertently got excess fuel into a cylinder, that could cause a
hydraulic lock. When you hit the starter, the piston tries to compress the
uncompressable fluid and stops. If your starter is strong enough, or if you
try to start it enough times, you could bend a rod. Pull the plugs out and
see if the starter works again.

John

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someone@some.domain - 11 Apr 2007 03:28 GMT

>>It looks like the carbs. have sealed themselves again after letting the fuel
>>sit for a while. Now the starter seems to be jammed. Any ideas whatrwould
[quoted text clipped - 7 lines]
>
>John

i would put the bike on the center stand and see if it will
kick start. if it runs, warm it up and go through the gears
carefully. keep that rear wheel up!
shut it off and then hit the switch. if it was stuck from
sitting, you may loosen it up.
you can also, with the engine OFF, put it in gear off the
stand and rock it gently.
many things can jame the starter, for exact help, go to one
of the many yahoo or google 650 yamay twin groups. lots of
really expert people and you won't waste your time on tests
that aren't really model specific.
then come back and share, ok?

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HotRdd - 11 Apr 2007 16:54 GMT

Thanks for the help guys, great advice. I'm also going to have a look at the
bendix gear tonight and see if it's warn.

>>>It looks like the carbs. have sealed themselves again after letting the
>>>fuel
[quoted text clipped - 24 lines]
> that aren't really model specific.
> then come back and share, ok?

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someone@some.domain - 11 Apr 2007 20:59 GMT

>Thanks for the help guys, great advice. I'm also going to have a look at the
>bendix gear tonight and see if it's warn.
[quoted text clipped - 27 lines]
>> that aren't really model specific.
>> then come back and share, ok?

keep us tuned.

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Motorcycle Forum / General / Yamaha / April 2007

76 Yamaha 650 spilling fuel?